Since its beginnings, SIMS has evolved along distinct paths depending on the application. The relentless progress of Moore’s law drove innovation in high-sensitivity mass spectrometers with atomic scale depth resolution and formed the “depth profiling” community. The requirements for organic and later biological applications were quite different driving innovation in imaging, reduced damage and the emission and detection of larger molecules giving rise to the “static SIMS” community. Tremendous progress was made in both evolutionary lines but was compartmentalised.

The last decade has brought revolutions in the ion beam technology and mass spectrometers that have brought a convergence to the field. For example, gas cluster ion beams enable molecular depth profiling with high-depth resolution and imaging with < 1 µm resolution. Innovation in mass spectrometers e.g. J105 (Ionoptika, UK) and OrbiSIMS (IONTOF, Germany) now bring the ability for high-duty cycle (sensitivity) that matches the performance on magnetic sector instruments used for semiconductor profiling but also with high-mass resolution and MS/MS capabilities for improved identification. Examples of these revolutions and convergence in the field will be provided.

The next decade will see further advances in mass spectrometers, for example multiple reflection ToF (Waters, UK) and hybrid analysers (e.g. Orbitrap-ASTRAL, Thermo) and improved sensitivity using quantum detection.

Battery research plays a crucial role in enabling the successful transition to the use of renewable energy sources by enhancing energy storage capabilities. To optimize battery performance, it is necessary to explore different concepts, including the integration of solid electrolytes in lithium-ion batteries and the utilization of lithium metal anodes. The performance of a battery is fundamentally influenced by the processes occurring at interfaces, particularly the formation of interphases when different components come into contact, which significantly impacts the kinetics of lithium transport. Understanding and characterizing these interphases and interfaces are pivotal in unraveling the mechanisms underlying impedance growth and related phenomena. Thorough analysis and characterization of electrodes, electrolytes, and their interfaces are essential for gaining insights into interface behavior, potential degradation processes, and for improving cell performance. This challenging task requires techniques with high lateral resolution, sensitivity, and the ability to provide chemical information.

In our research, we employ secondary ion mass spectrometry (SIMS) and complementary X-ray photoelectron spectroscopy (XPS) to comprehensively characterize both the raw materials and various components of a battery cell. Our analysis encompasses surface analysis, conventional depth profiling, and surface imaging, enabling us to perform analytical 3D tomography. Additionally, we utilize focused ion beam (FIB) crater preparations to assess interfacial phenomena over larger areas.

By leveraging the capabilities of time-of-flight secondary ion mass spectrometry (ToF-SIMS), we have acquired valuable insights into chemical and structural information at the nanometer scale, surpassing the capabilities of other techniques. This progress brings us closer to our goal of improving our understanding of the fundamental mechanisms governing cell performance, degradation, and transport phenomena in lithium (ion) batteries. Such knowledge is crucial for further advancements in battery technology and the realization of efficient and sustainable energy storage solutions

Titanium dioxide (TiO₂) surfaces are extensively utilized in various applications, including dye-sensitized solar cells (DSSCs),¹ biomaterial,² and photocatalysis³ due to their cost-effectiveness, stability, and suitable electronic properties. More recently, in solar cell applications, the use of functionalized anatase has been reported.⁴ Among the numerous functional groups, carboxylic acid (-COOH) is one of the most common surface modification candidates widely used in DSSCs. However, one of the drawbacks of anatase TiO₂ is its relatively low reactivity towards carboxylic acid anchor groups compared to other metal oxides⁵. Since Ni, Co, and Cu have reportedly shown a higher affinity towards –COOH groups,^5,6 we exploit the intrinsic affinity of these metals in the form of bilayers to enhance titania's reactivity. Herein, we develop metal-phosphate bilayers containing nickel (Ni), cobalt (Co), copper (Cu) and manganese (Mn) synthesized on anatase TiO₂ compact oxide as these metals facilitate attachment to carboxylic acid-based compounds. The successful formation of these bilayers was confirmed through comprehensive characterization techniques, including Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Cyclic Voltammetry/Electrochemical Impedance Spectroscopy (CV/EIS), demonstrating the effectiveness of the phosphate layer as an intermediate between TiO₂ and the other metal species.

Furthermore, we specifically investigate copper metal-phosphate bilayers for biomaterial applications, as copper has well-known antibacterial properties that can contribute to the prevention of bacterial growth and infection. Herein, we validate the successful reactivity of copper by investigating the TiO₂-P-Cu sample’s influence on enzymatic activity.

The findings provide valuable insights into developing reactive surfaces with potential applications in surface modification for application both in photocatalysis and the biomedical field, aiding in the prevention of potential pathogenic interactions.

Keywords: Anatase TiO₂, copper, ToF-SIMS, bi-phosphate bilayer, reactivity

References:

[1] Gong, J., Sumathy, K., Qiao, Q., & Zhou, Z. (2017). Review on dye-sensitized solar cells (DSSCs): Advanced techniques and research trends. Renewable and Sustainable Energy Reviews, 68, 234–246. https://doi.org/10.1016/J.RSER.2016.09.097

[2] Killian, M. S., & Schmuki, P. (2014). Influence of bioactive linker molecules on protein adsorption. Surface and Interface Analysis, 46(S1), 193–197. https://doi.org/10.1002/sia.5497

[3] Linsebigler, A. L., Lu, G., & Yates, J. T. (1995). Photocatalysis on TiO₂ Surfaces: Principles, Mechanisms, and Selected Results. Chemical Reviews, 95(3), 735–758. https://doi.org/10.1021/CR00035A013/ASSET/CR00035A013.FP.PNG_V03

[4] Monteiro, M. C. O., Schmuki, P., & Killian, M. S. (2017). Tuning Anatase Surface Reactivity toward Carboxylic Acid Anchor Groups. Langmuir, 33(49), 13913–13922. https://doi.org/10.1021/ACS.LANGMUIR.7B03044/SUPPL_FILE/LA7B03044_SI_001.PDF

[5] Monteiro, M. C. O., Cha, G., Schmuki, P., & Killian, M. S. (2018). Metal-Phosphate Bilayers for Anatase Surface Modification. ACS Applied Materials and Interfaces, 10(7), 6661–6672. https://doi.org/10.1021/acsami.7b16069

[6] Meychik, N., Nikolaeva, Y., Kushunina, M., & Yermakov, I. (n.d.). Are the carboxyl groups of pectin polymers the only metal-binding sites in plant cell walls? https://doi.org/10.1007/s11104-014-2111-z

Composite solid electrolytes (CSEs), consisting of polymer and ceramic electrolytes, have garnered significant attention as promising materials for advanced energy storage systems, owing to their improved mechanical stability and enhanced ionic conductivity. Understanding the diffusion pathways of lithium ions within CSEs is crucial for optimizing their performance and designing efficient energy storage devices. The in-situ investigation of lithium ion diffusion pathways in CSEs using Secondary Ion Mass Spectrometry (SIMS) imaging is a novel approach to understand the lithium ion transport process in composite electrolyte systems. In our case we studied the diffusion behavior of lithium ions in the composite electrolyte system of polyethylene oxide (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as polymer electrolyte matrix, and lithium lanthanum zirconate (LLZO) as ceramic electrolyte filler.

To achieve this, we perform in-situ SIMS analysis utilizing a custom-designed sample holder that enables electrical contact to a potentiostat. This innovative setup allows us to directly observe and quantify lithium ion diffusion within the CSEs during electrochemical cycling. The symmetric electrochemical cell used in our experiments consists of ⁶Lithium metal as the reference electrode, the PEO:LiTFSI and LLZO composite solid electrolyte, and lithium metal as the counter electrode. By cycling the cell within the SIMS chamber, we can monitor the real-time lithium ion diffusion processes, providing valuable insights into their dynamic behavior within the CSE.

Cross sections of the investigated cell setup were created beforehand by an ion polishing system, establishing optimal conditions for the following in-situ ToF-SIMS imaging. Using the ⁶Lithium isotope, we map the distribution and quantify the diffusion of lithium ions within the CSEs. The obtained SIMS data reveals the evolution of lithium ion isotope concentration gradients, diffusion pathways, and interfacial reactions between the polymer and ceramic components during cycling. Our analysis highlights the significance of these findings in elucidating the underlying mechanisms governing lithium ion transport in CSEs.

Within the specific CSE system of PEO:LiTFSI and LLZO, we conduct a detailed analysis of the observed lithium ion diffusion behavior based on various factors. We study the influence of polymer-to-ceramic ratio, temperature and current density on lithium ion diffusion pathways within the composite electrolyte system. Our in-situ SIMS analysis provides valuable insights into the role of interfacial dynamics in the CSEs, aiding in the development of strategies to achieve enhanced ionic conductivity and stability.

Safety, cycle life and performance of next-generation batteries need a stable solid electrolyte interphase (SEI). Understanding the nature, properties, composition, and structure of the SEI is critical to stabilising the next-generation batteries. The SEI layer is vital for lithium during battery cycles, as lithium ions need to pass through the SEI layer before reaching the bulk electrode. Formation of the SEI layer has an advantage of inhibiting further electron transmission from the electrode toward electrolyte, so avoiding further decomposition of electrolyte and enhancing battery performance. A change in the composition and/or shape of the SEI layer dramatically alters cell performance. Despite its great importance, the SEI layer is poorly understood due to its complexity, non-uniformity, and very thin thickness.

To understand the SEI layer, it is important to correlate the standard materials data from techniques including secondary ion mass spectrometry (SIMS) and hard X-ray photoelectron spectroscopy (HAXPES).HAXPES provides quantitative analysis of standards with a depth range of up to 100 nm. SIMS is generally considered a semi-quantitative technique, however, in contrast to HAXPES, SIMS is very sensitive to lithium compounds and can obtain high-resolution 2D or 3D images of the sample. The use of massive gas cluster ion beams (GCIBs) enables few-nm depth resolution deeper than 10 μm. Therefore, HAXPES and SIMS complement each other in the study of SEI layer.

Here a study of standard metal oxides with SIMS and HAXPES and investigation of the SEI layer of lithium-ion batteries is presented. Analysis of standard materials are important in solid-state physics and the development of next-generation energy storage devices. Here we investigated the analysis of various metal oxides related to LiNi_xMn_yCo_zO₂ (NMC) used as cathode in lithium-ion batteries. In SIMS, these samples were analysed using 70 keV GCIB. The obtained spectrum depends on the chemical nature of the primary ion and its velocity [1]. The primary ions of (CO₂)_n and (H₂O)_n were found to increase the relative yields of metal oxides and metal hydroxides compared to Ar_n ions. HAXPES is a powerful technique to investigate the electronic behaviour of the transition metals (TMs) oxides. HAXPES with a gallium x-ray source can be accessible to the 1s orbitals of the first-row transition metals. Due to the absence of the multiplet splitting of the core level and the spin-orbit splitting of the 1s core electrons, its XPS spectra is sensitive to the chemical environment and to the non-local charge transfer screening. Therefore, XPS 1s spectra of TMs can be used to recognize the charge-transfer satellite feature and to discriminate local and non-local screening characters. This can be used to accurately determine the oxidation states of the transition metals.

[1] A.H. Alsaedi, A.S. Walton and N.P. Lockyer, Secondary Ion Mass Spectrometry analysis of metal oxides using 70 keV argon, carbon dioxide and water gas cluster ion beams, J. Vac. Sci. Technol. B (2023) [in press]

Research into lithium ion batteries (LIBs) for electric vehicles has been accelerated in the last decades. For the Ni-rich layered materials functioning as the cathode in LIBs, the high capacity and low cost make it a promising candidate for high-energy batteries while its poor thermal and chemical stability, unsatisfying cycling behavior, and sensitivity to ambient moisture hinder its further applications. Considerable attempts have been performed on improving the performance of the Ni-rich cathode. However, to enhance the performance and safety of LIBs, it is essential to understand the degradation processes occurring both within the electrode materials, as well as at the electrodes/electrolyte interfaces. Preliminary degradation studies have already been carried out on intragranular cracks [1], phase transition with oxygen evolution [2] etc. analysis but the local chemical degradation processes on the utmost surface, at interfaces and in the bulk materials are yet to be fully unfolded.

To obtain more chemical information on the interface of the electrolyte and electrode, burgeoning investigations with Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS) have been reported on lithium ion batteries, due to its surface sensitivity and the capability of depth profiling. However, the complexity of the chemical environment of battery electrodes and the instrumentation fundamentals increase the barrier for understanding the authentic behavior. In this work, studies on the chemical degradation process at the interface of the high Ni content positive electrode material LiNi_0.8Co_0.1Mn_0.1O_2-d (NCM811) has been performed by ToF-SIMS together with different surface-sensitive techniques. Furthermore, a unique plasma focused-ion-beam secondary ion mass spectrometry (FIB-SIMS), Hi-5, with unprecedent sensitivity to low mass elements coupled to a lateral resolution of 30 nm and simultaneous detection of both positive and negative ion is applied for the first time. To further deconvolute the solid-electrolyte interface (SEI) chemistry low energy ion scattering (LEIS) with utmost surface sensitivity is employed. The chemical environment and roles of different elements in the degradation processes of the cathode materials will be investigated and discussed.

Reference

[1] Z. Xu et al., J. Mater. Chem. A, 6 (2018) 21859

[2] R. Jung et al., J. Electrochem. Soc., 164(7) (2017) A1361

Bio-analysis by SIMS is not new. There are nice examples in the literature dating back 50 years!

However, that does not mean there has not been significant progress that has expanded our capabilities for extracting information from these impressively complicated samples.

This presentation details some of the journey that bio-SIMS has made and looks forward to exciting prospects, and challenges, that lie ahead.

Environmental stresses such as nutrient restriction or hypoxia can lead to fetal growth restriction. It is well established, however, that growth decreases less in the CNS than in other organs, an effect known as brain sparing (Gruenwald, 1963 PMID: 14081642). The molecular mechanisms underlying brain sparing are not yet fully understood. We previously demonstrated that the Drosophila larval brain recapitulates may of the features of mammalian brain sparing (Cheng et al., 2011 PMID: 21816278; Bailey et al., 2015 PMID: 26451484; Lanet et al., 2013 PMID:23478023). To investigate how brain sparing changes metabolism in the larval brain, we have been developing ambient temperature and cryogenic workflows for mass spectrometry imaging using our recently developed OrbiSIMS instrument (Parsarelli et al., 2017 PMID: 29131162; Newell et al., 2020 PMID: 32603009). OrbiSIMS provides high lateral and mass resolution simultaneously, enabling metabolite imaging at a near-cellular level. In this study, we use OrbiSIMS to map the localizations of more than 100 polar and apolar metabolites in the larval CNS. We also conduct a spatial lipidomics survey of the effects of environmental stresses upon larval CNS metabolism.

OrbiSIMS combines high-resolution imaging using a focused gas cluster ion beam with an Orbitrap mass spectrometer to enable sub-cellular resolution imaging with high mass-resolving power^[1]. The ability to perform cryogenic measurements is valuable, as it enables imaging in the native state^[2,3] and of volatile molecules in ultra-high vacuum^[2].

High-resolution imaging creates the challenge of detecting sufficient ions within a pixel. To enable improvements in spatial imaging capability, the secondary ion yield must improve concomitantly. Previous studies have shown improved ion yield using water cluster beams^[4] or hydrated samples^{[3, 5]}. Additionally, it has been shown that the positive ion yield decreases with lipophilicity (Log P) of a compound^[6], thus degrading the detection sensitivity for polar tumour metabolites as well as drugs designed for improved solubility.

Here, we present targeted and untargeted assessments of the secondary ion yield enhancement of a range of endogenous biomolecules within frozen-hydrated mouse liver tissue when compared to in situ freeze-dried tissue. To ensure equivalence of molar amounts the secondary ion signal was integrated over a fixed area for the entire thickness of tissue. In positive polarity, we show an enhancement up to three orders of magnitude, and the relative enhancement increases for polar molecules (low Log P). In negative polarity, no enhancement is observed supporting the hypothesis that increased protonation aids ionisation. We provide an assessment of the secondary ion yield enhancement with respect to classes of biomolecule and to mass.

We demonstrate the benefits of cryo imaging for biological tissues in terms of signal and structural integrity. This supports future work to improve OrbiSIMS spatial resolution.

[1] M. K. Passarelli, A. Pirkl, R. Moellers, D. Grinfeld, F. Kollmer, R. Havelund, C. F. Newman, P. S. Marshall, H. Arlinghaus, M. R. Alexander, A. West, S. Horning, E. Niehuis, A. Makarov, C. T. Dollery, I. S. Gilmore, Nat Methods 2017, 14, 1175-+.

[2] C. L. Newell, J. L. Vorng, J. I. MacRae, I. S. Gilmore, A. P. Gould, Angew Chem Int Edit 2020, 59, 18194-18200;

[3] J. T. Zhang, J. Brown, D. J. Scurr, A. Bullen, K. MacLellan-Gibson, P. Williams, M. R. Alexander, K. R. Hardie, I. S. Gilmore, P. D. Rakowska, Anal Chem 2020, 92, 9008-9015.

[4] K. D. Nilsson, A. Karagianni, I. Kaya, M. Henricsson, J. S. Fletcher, Anal Bioanal Chem 2021, 413, 4181-4194.

[5] X. A. Conlan, N. P. Lockyer, J. C. Vickerman, Rapid Commun Mass Sp 2006, 20, 1327-1334.

[6] J. L. Vorng, A. M. Kotowska, M. K. Passarelli, A. West, P. S. Marshall, R. Havelund, M. P. Seah, C. T. Dollery, P. D. Rakowska, I. S. Gilmore, Anal Chem 2016, 88, 11028-11036.

The estimated size of the global agrochemicals market in 2022 amounted to USD 227.9 billion with a projected increase to USD 234.27 billion in 2023 [Market Analysis Report 2018-2022]. The notable increase in agrochemical usage observed worldwide can be attributed to the considerable economic benefits that accrue to farmers through the safeguarding of crops against invasive species, including the improvement in quality and quantity of harvests. However, limited knowledge of the in-situ chemical composition of wheat leaves and the permeation mechanisms of pesticides into skin and leaf tissues restricts research and development of new products.

The 3D OrbiSIMS has been recently demonstrated as a powerful tool for skin research, providing label-free insight into the 3D permeation profiles of endogenous and exogenous compounds [Starr et. al., 2022] characterizing the molecular composition of the stratum corneum and tracking the permeation of a Pal-GHK peptide. Building upon these advancements, our study extends the application of 3D OrbiSIMS to explore the native chemistry of wheat leaves, with a focus on the plant cuticle as the primary diffusion barrier. The study also illustrates the distribution of a fungicide formulation across wheat leaves and skin, providing insights into the formulation's diffusion in two relevant biological matrices.

The molecular architecture of wheat leaves was first probed, with a focus on the cuticle. In-situ analysis provided novel insights into the localisation of endogenous species, including fatty acids, amino acids, phospholipids, flavones and vitamins. Depth profiling revealed non-homogeneity of the leaf as a function of depth where the distribution profiles of fatty acids and aldehydes associated with the cuticle and epicuticular waxes displayed a pronounced abundance at the surface of the leaf. Conversely, flavones and vitamins were predominantly localised in the epidermis.

Exogenous compounds were successfully identified in both skin and wheat leaves, in addition to the endogenous species. The investigation focused on evaluating the impact of exposure time and concentration on the permeation of a fungicide formulation across skin and wheat leaves. Utilizing in situ analysis, the entire formulation was concurrently detected and tracked, even at 100 ppm. The active, cyproconazol, displayed increased permeation with prolonged exposure time, and higher concentrations resulted in a higher relative quantity in both matrices. Co-formulants showed diverse localization patterns, with carrier solvents resembling the permeation of the active ingredient, while emulsifiers remained primarily at the surface, as expected.

Our findings highlight the 3D OrbiSIMS' potential to detect native and exogenously delivered chemistries in skin and leaf samples, enabling comprehensive observation of all components of the investigated formulation. The molecular elucidation and permeation insights obtained from this approach could be implemented in designing agrochemical formulations with targeted delivery and reduced associated issues.

Various techniques are available to measure mechanical properties such as material hardness, for example, nanoindentation. However, certain materials or structures provide challenges to measuring actual hardness, such as when an underlying material is much softer than the one above it (e.g., an ice cube sitting on water).

Water Cluster SIMS is a technique with the potential to simultaneously obtain information on both molecular and mechanical properties of materials. Since water clusters are more robust than other popular clusters such as Ar clusters, it has been observed in Water Cluster SIMS spectra that water cluster ions colliding with a surface dissociate into smaller ions with the formula [(H₂O)_n+H]⁺ or [(H₂O)_n+OH]^-, where 2 ≤ n.

The ion intensity ratios for the ion yield (e.g. [(H₂O)₂+H]⁺/ Σ[(H₂O)_n+H]⁺) are highly sensitive to the mechanical properties of materials. The intensity ratio called ‘dissociation ratio’ appears to depend on the surface's mechanical properties and the energy of the ion beam. In other words, we see high signals of back-scattered water cluster ions at a low ion beam energy for the dissociation ratio as well as enhanced sensitivities of high-mass compounds.

A previous study demonstrated a good relationship between Young's modulus and the dissociation ratio using observed ion intensities on substrates including metals and polymers. The ability to measure the mechanical properties of a surface in situ whilst performing SIMS measurements would be beneficial for materials where other measurements have failed. We examine whether the use of water cluster SIMS may also be used to measure rigidity on more complex biological structures and whether the parameters of the cluster should be similar to those used for harder materials.

Glycosaminoglycans (GAGs) are important biopolymers situated within the peri-cellular and extra-cellular spaces that have multiple biological roles. They are complex molecules with variations in sulphation, acetylation and epimerisation that results in different biological behaviour.

Secondary ion mass spectrometry (SIMS) has increasingly been used for analysing biological samples, with a wealth of studies on DNA and proteins but limited analysis of GAGs. In this presentation I will present my recent endeavours to address this gap, making use of gene-editing tools to create robust biological reference samples and high mass resolution Orbi-SIMS analysis to enable identification of GAG-derived ions. I will demonstrate the utility of SIMS as an effective tool to probe the complexity of GAGs within biological samples.

With the increasing global demand for food, the need to produce newer crop-protection products is also growing for efficient and productive farming. For the commercial production of agrochemicals, it is pivotal to understand their distribution and metabolism in the plant system. The method currently used to understand this is autoradiography, a tedious technique usually done at the far end of product development. In this study, we aim to develop more convenient, alternate methodologies for imaging xenobiotics with mass spectrometry.¹ The main bottleneck to doing so is that there are no well-established protocols for sample preparation and application of xenobiotics to study localization in plants compatible with mass spectrometry imaging.² Hence, we are trying to identify suitable mass spectrometry imaging technologies including SIMS, DESI and MALDI for analysis and the corresponding sample preparation taking Azoxystrobin as a model fungicide along with wheat and tomato plants as model plants.

The main aim of this study is to visualize the localization of xenobiotics once applied to the leaf across the leaf lamina and veins and into the depths of the leaf. Initially, the analysis parameters for Azoxystrobin formulation were identified for different MSI techniques. To understand the surface localization of xenobiotics once absorbed into the leaf, the direct analysis of the leaf surface is futile. Hence, some surface modifications like chloroform dipping of the leaf or indirect analysis by forceful leaf imprinting onto another porous surface need to be done. Complimentary to this, cryo-embedding and cryo-sectioning of leaves could be done to understand the depth penetration of the applied xenobiotics. We explored the possibilities of direct and indirect analysis of leaves with different materials and found porous PTFE to be one of the best possible options to understand surface localizations. Since leaf tissues are quite fragile, for sectioning, we also explored the best embedding conditions for them like appropriate embedding media and pre- and post-sectioning methods to produce the best sections possible without chemical delocalization. For sectioning, we also explored the use of specialized mass spectrometer-compatible tapes to reduce sample damage while sectioning.

Such sample preparation and analysis methodologies could be used for understanding the time-dependent localization of agrochemicals when applied to the plant leaves and could act as a complementary technique to the existing visualization methodologies to produce safer agrochemicals.

References:

1. Lorensen, M. D. B. B., Bjarnholt, N., St-Pierre, B., Heinicke, S., Courdavault, V., O'Connor, S., & Janfelt, C. (2023). Spatial localization of monoterpenoid indole alkaloids in Rauvolfia tetraphylla by high resolution mass spectrometry imaging. Phytochemistry, 209, 113620.

1. Ajith, A., Milnes, P. J., Johnson, G. N., & Lockyer, N. P. (2022). Mass Spectrometry Imaging for Spatial Chemical Profiling of Vegetative Parts of Plants. Plants, 11(9), 1234.

The worldwide experience with the COVID 19 pandemic demonstrated once more that without the prevention and the development of specific pharmaceutical products the reduction of the risk of infection can be achieved only by tracing positive cases while imposing strong restrictions to the population. However, this type of measures affected dramatically the economy and the social activities making the research to find a vaccine very urgent and necessary.

The development of vaccine is not an easy task especially when pure antigens are employed for reducing vaccine immunogenicity. This requires the use of adjuvants to optimize vaccine effects whilst maintaining its safety.

Adjuvants based on Aluminium salts are amongst the most used because of its high safety profile, whilst its mechanisms of actions remain unclear.

In this work, we present a detailed surface analysis by means of Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoemission Spectroscopy (XPS of a polymeric platform to be used for vaccine development and delivery. This platform consisted in Al containing polymer substrate prepared in two different formulations, namely micro-Alum and nano-Alum. The effectiveness of the Alum-platform was tested against ovalbumin (OVA) protein.

Both XPS and ToF-SIMS were able to deliver information about the interaction of the ovalbumin and the substrate. In particular, results indicate that, independently of the substrate formulation (micro or nano), a ratio of Alum/OVA of 3:1 was required to reach saturation. These results were confirmed by SDS-PAGE gel measurements where the 3:1 ratio was the first supernatant sample in which OVA protein could be detected. Moreover, circular dichroism analysis on Al:OVA complexes shown a conformational change of the protein secondary structure upon adjuvant binding.

Unraveling characteristic compositional patterns of extracellular matrices (ECM) promises new insights into mechanistic biology, unprecedented bioengineering options, and progress in medical diagnostics. Analytical techniques to reliably identify ECM variants are therefore of high and growing interest. Since many standard approaches (immunostaining, enzyme-linked immunosorbent assays, Western blotting) applied for that purpose require prior knowledge of the sample and/or tedious sample processing, mass spectrometry approaches are increasingly considered a valuable and widely explored alternative. Our study [1] for the first time demonstrates the potential of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to detect subtle differences between human mesenchymal stromal cell (MSC)-secreted matrices as induced by exogenous stimulation or emerging pathology. For that aim, ToF-SIMS spectra of decellularized ECM samples were evaluated by discriminant principal component analysis (DPCA), an advanced multivariate analysis technique, to decipher characteristic compositional features. To establish the approach, signatures of major ECM proteins were determined from samples of pre-defined mixtures. Based on that, sets of ECM variants produced by MSCs in vitro were analyzed. Differences in the content of collagen, fibronectin, and laminin in the ECM resulting from the combined supplementation of MSC cultures with ascorbic acid and macromolecular crowding agents could be detected by DPCA of ToF-SIMS spectra. The results were verified by immunostaining. Finally, the comparative ToF-SIMS analysis of ECM produced by MSCs of healthy donors and patients suffering from myelodysplastic syndrome (MDS), a disease that arises from genetically altered hematopoietic stem cells in the bone marrow, displayed the potential of the methodology to reveal disease-associated alterations of the ECM composition.

[1] R. Zimmermann, M. Nitschke, V. Magno, U. Freudenberg, K. Sockel, F. Stölzel, M. Wobus, U. Platzbecker, C. Werner, Small Methods 2023, 2201157

Three dimensional (3D) ToF-SIMS depth profiles produce large and complex hyperspectral data sets. Interpretation requires that the complexity of these data sets is reduced. Individual ion peaks are often extracted and displayed in 3D or a handful of peaks are plotted in one dimension as a function of depth. This method works well for simple samples, or for samples with a well-defined structure. In the case of complex or unknown samples or for those with important spatial information in the x-y plane, these methods struggle to convey the depth of information captured within the data set. The specific choice of individual ion peaks has the potential to impart user bias and make a significant difference to the interpretation of results as only a tiny fraction of the original data has been considered or displayed.

We have developed an alternative method which considers all or an analyst-specified sub-set of ion peaks within a given depth profile. Unsupervised machine learning, specifically self-organizing maps with relational perspective mapping (SOM-RPM), is employed to create a colour-coded similarity map in which changes in colour are specifically graded to accord with changes in molecular state. The complete 3D depth profile can then be visualized, providing a unique picture of the local and global mass spectral relationships between individual voxels.

The visualisation using a similarity map makes distinct regions of depth profiles easily visible and repeated layers immediately recognisable. Interfacial regions are highlighted as distinct areas allowing for in-depth chemical analysis. SOM- RPM allows the spectra from each region to be extracted for identification and comparison to other regions, making it an excellent technique for exploring unknown or complex samples..

This work will present detailed studies of conducting polymer aerospace coatings and double silver low emissivity coatings, illustrating 3D depth profiles which consider the totality of the mass spectrum at every voxel. Using SOM-RPM to analyse the data yields an intuitive visualisation of 3D depth profiles, highlights any structural flaws such as pinholes, illustrates the degree of interfacial mixing and allows for in depth spectral analysis of selected regions. The SOM-RPM methodology has proven to be a robust technique that offers a substantial advance in this field.

One of the long-term objectives of ToF-SIMS research has been the high resolution 2D and 3D imaging of pharmaceuticals and biomolecules in tissues and biofilms at physiologically relevant concentrations. Although much progress has been made through advances in instrument design and development of cluster ion sources, the technique continues to be limited by low signal-to-noise ratio for many important systems. Improving signal-to-noise, and thereby image contrast, is one of the key challenges needed to expand the useful applications of ToF-SIMS. Although a variety of multivariate analysis (MVA) methods have proven to be effective for improving image contrast in ToF-SIMS, the distribution of important but low intensity ions can be obscured in the MVA analysis, leading to a loss of chemically specific information. Furthermore, the results from MVA methods can often be challenging to interpret.

We have developed an alternative approach in multivariate analysis of mass spectrometry images: inverse maximum signal factors (iMSF) denoising. Standard MVA methods produce scores and loadings which can be difficult to interpret. In contrast, the output from iMSF is a denoised image for each of the original mass peaks. To strengthen the approach, five tests have been developed to validate the denoised images. Results of denoising for 2D and 3D images will be presented. Using this approach, a signal-to-noise improvement of as much as two orders-of-magnitude has been demonstrated. This tool, however, can do more than just make high contrast images. Combining iMSF denoising with Pearson’s correlation coefficients can be used to assist with clear interpretation of the classical MVA results. In some cases, it is even possible to obtain MS/MS-like information that can assist in unambiguous compound identification. iMSF denoising can also be used as a core part of image fusion algorithms that combine mass spectral images with a variety of complementary imaging methods. This tool allows researchers to more quickly visualize, identify and validate key features in mass spectrometry imaging data sets. iMSF denoising is a powerful addition to the suite of image processing techniques available for studying mass spectrometry images.

In OrbiSIMS [1], secondary ions are accelerated by an extraction electrode and using a switching electrode can either pass directly to a time-of-flight (ToF) analyser or be deflected to a transfer system to an Orbitrap^TM analyser. In that case, a quasi-continuous stream of secondary ions is injected into a special ion trap where they revolve around a central spindle shaped electrode and oscillate along it with a frequency inversely proportional to the square root of the mass of the ion. An image charge is created in a pair of outer electrodes and is measured with time. This time-domain transient signal is converted to frequency (and hence mass) domain by a Fourier transform and has signal processing.

At NPL, we have established a metrology (measurement science) programme to study three key interconnected properties of OrbiSIMS: transmission, signal, and noise to improve measurement reproducibility. For example, we took advantage of the stable 30 keV Bi_n⁺ primary ion beam to report measurements of noise across a range of ion intensities and created a statistical model that was used to develop a data scaling strategy that accounts for non-uniform noise across a mass spectrum and has important implications for multivariate statistical analysis methods such as principal component analysis (PCA) [2]. As part of the transmission study, we conducted a systematic assessment of two key parameters, the target potential, V_T, and the collision cell pressure, P, in the transfer optics on the transmitted secondary ion intensities [3]. We revealed a complex behaviour, indicating the possibility for additional separation of ions based on their shape, stability, and kinetics of formation [4].

We use this measurement base to assess linearity of the signal intensity scale. We systematically varied the number of secondary ions sent to the Orbitrap and extracted metrics showing that non-linearity in signal arises from space-charge effects in the trap and is mass-dependant. These findings have direct implication on applications including depth profiling and imaging.

[1] M. K. Passarelli et al., “The 3D OrbiSIMS—label-free metabolic imaging with subcellular lateral resolution and high mass-resolving power,” Nat. Methods, no. november, p. nmeth.4504, 2017, doi: 10.1038/nmeth.4504.

[2] M. R. Keenan et al., “In preparation.”

[3] L. Matjacic et al., “OrbiSIMS metrology part I: Optimisation of the target potential and collision cell pressure,” Surf. Interface Anal., no. November 2021, pp. 1–10, 2021, doi: 10.1002/sia.7058.

[4] G. F. Trindade et al., “In preparation.”

The field of implant systems is recently entering a new area of integrating drug delivery coating on the surface of the implant material to improve biocompatibility, treat possible inflammation, and resist bacterial infection.¹ These factors remain an intractable problem to a successful implant application. The conventional drug delivery route is inefficient in addressing these challenges due to its inherent limitation such as lack of selectivity, toxicity, short circulation time, and sometimes poor patient compliance.² The coating of nanoporous/nanotubular material on the implant is currently been investigated as a solution to achieving improved biocompatibility and the loading of drugs into these structures can serve to attain a localized and targeted delivery medium. Here, we present a strategy for improving the drug release characteristics in terms of limiting the undesireable initial burst release and extending the total release time via structral modification of zirconia nanotubes. Furthermore, efforts at improving the antibacterial properties of the coating by decorating with silver nanoparticles were also demonstrated. The modified zirconia nanotubes were characterized via SEM, XPS, and ToF - SIMS, while the drug release properties were monitored via UV - Vis spectroscopy. The depth profile image obtained by combining FIB and ToF - SIMS measuremnt confirms the loading of the drug along the length of the nanotube. These modifications illustrate a simplifiedand effective approach toward optimizing the interface between the host environment and the biomaterial surface to meet the very important criteria of biocompatibility and antibacterial properties.

References

(1) Pioletti, D.; Gauthier, O.; Stadelmann, V.; Bujoli, B.; Guicheux, J.; Zambelli, P.-Y.; Bouler, J.-M. Orthopedic Implant Used as Drug Delivery System: Clinical Situation and State of the Research. Curr. Drug Deliv. 2008, 5 (1), 59–63. https://doi.org/10.2174/156720108783331041.

(2) Losic, D.; Aw, M. S.; Santos, A.; Gulati, K.; Bariana, M. Titania Nanotube Arrays for Local Drug Delivery: Recent Advances and Perspectives. Expert Opin. Drug Deliv. 2015, 12 (1), 103–127. https://doi.org/10.1517/17425247.2014.945418.

Information on hydrogen, carbon and oxygen impurities (atmospheric gas species) introduced during processing and/or ageing is of major importance for a better understanding of semiconductor device lifetime and failure modes. Dynamic SIMS is often used in evaluating the concentration of impurities in solids because of its high sensitivity and depth profiling capabilities with good depth resolution and high throughput. Continuous ion beam sputtering with high density primary beam provides high sensitivity and reduced background contribution from residual gases within the analytical chamber. There is no difference between magnetic sector (MS) and Time of Flight (TOF) SIMS instruments performance as soon as a dynamic SIMS mode is used (continuous sputtering mode). Both the MS-SIMS and TOF-SIMS tools are supplied with UHV analysis chamber with optimized vacuum conditions, minimizing the background level created by residual gases sticking to the sample surface. High density Cs primary ion beam is often used because of high electronegativity of most of light element species, so, the Cs surface retention increases the negative secondary ions yield. Reducing the sputtering energy leads to increased Cs surface retention, thus, the ion yield. At the same time, it increases the surface accommodation of oxygen containing molecular species from the vacuum atmosphere (gettering effect). The variation of Cs retention can be also observed in multi-layered structures depth profiles (e.g. SiGe), when sputter yield is drastically changing from layer to layer. So, the oxygen background varies more than expected from ionization yield variation, observed during the calibration step. A modeling experiment can be performed, allowing us to estimate the background from the vacuum atmosphere. A comparison of continuous sputtering and using an interleaving sputtering mode (TOF or beam blanking) allows a direct measurement of background signal contribution from the vacuum. The difference in sputtering cycle between continuous sputtering mode and interleaving mode produces the time when molecular species were deposited from the vacuum. The difference in the background signal normalized to the sputtering cycle time can be safely subtracted from the depth profile and allows the improvement of the detection limit valid for both dynamic SIMS and TOF-SIMS instrumentation. The problem associated with SIMS data noise treatment is a subject of current study. The statistical analysis of oxygen (hydrogen) detection limits, observed with MS- and TOF-SIMS instruments will be presented.

ToF-SIMS is a very versatile and widely applicable method, but it also has its weaknesses with the most profound one being nonquantitative analysis caused by the matrix effect which also limits the capabilities of depth profiling. Namely, in SIMS depth profiling of thin films, chemically similar layers can be difficult to distinguish between each other and interfaces between them difficult to identify. The reason for this is changes in the ionization yield caused by the changes in the matrix as the chemical composition of the sample differs from layer to layer. This is the same effect that causes non-quantitative surface analysis and matrix-dependent detection limits of the same molecule or element. However, there are different ways of reducing the matrix effect. Most widely applied are laser or electron beam post ionization (SNMS), metal-assisted and matrix-enhanced SIMS, dynamic reactive ionization (DRI) and introduction of gases into the analysis chamber (gas flooding).

We applied the gas flooding approach to reduce the matrix effect and improve depth profiling results, testing different atmospheres such as H₂, C₂H₂, CO and O₂ during the analysis. Only O₂ was previously used, while the other three gases were introduced as a novelty by our group. We achieved the best results with the H₂ both in the field of depth profiling and the quantitative aspect of the results measured with the mass spectra. H₂ atmosphere enables easier and unambiguous differentiation of layers of metals and their oxides, different metals, and alloys with different compositions. Furthermore, the identification of interfaces becomes simpler. We also did not observe a change in the sputter rate during H₂ flooding. [1] Surface roughening caused by the ion bombardment taking place during depth profiling was reduced in the H₂ atmosphere as well. This effect is more evident after sputtering a greater amount of the material and also depends on the chemical composition of the layer of interest. We assume that the most probable reason for this observation is the level of amorphization that happens during the sputtering process. [2] Our last results also show a better correlation between ratios of the SIMS signals from metals in alloys when comparing alloys with different chemical compositions analyzed in the H₂ atmosphere. The O₂ atmosphere also gives better results than UHV conditions, but improvement is less pronounced than in the case of H₂ flooding. These findings bring ToF-SIMS one step closer to becoming at least a semiquantitative method.

[1] J. Ekar, P. Panjan, S. Drev, J. Kovač. ToF-SIMS Depth Profiling of Metal, Metal Oxide, and Alloy Multilayers in Atmospheres of H₂, C₂H₂, CO, and O₂. J. Am. Soc. Mass Spectrom. 2022, 33, 31– 44.

[2] J. Ekar, J. Kovač. AFM Study of Roughness Development during ToF-SIMS Depth Profiling of Multilayers with a Cs⁺ Ion Beam in a H₂ Atmosphere. Langmuir 2022, 38, 12871–12880.

The effects of light particle - electrons, protons, alfa particles - irradiation on silicon have been extensively studied for decades. Irradiation-induced lattice damage has been found to be responsible for N-type doping of silicon, and charge carrier lifetime shortening. The use of protons allows to create deep implanted regions, with lower beam energies and less implantation-induced damage compared to heavier species. Beneficial effects of low/medium dose proton irradiation have been observed for a variety of power devices, such as Fast Recovery Diodes (FRDs), Insulated Gate Bipolar Transistors (IGBTs), Gate Turn-Off (GTO) Thyristors, where improvements of switching properties have been attributed to charge carrier lifetime shortening resulting from irradiation. More recently, attention has been put on multiple proton implantation to achieve a more fine control on device electrical properties, and industrial scaling of the manufacturing process has been taken into consideration during the last years.

The realization of an efficient analysis protocol is of primary importance in this context, and the characterisation of such structures by depth profiling techniques is always required. Spreading Resistance Profiling (SRP) is commonly used to measure electrical depth profiles, and it finds application wherever the implanted species produce modifications of the substrate doping level. It has been found that electrical profiles of proton-implanted silicon resamble implantation-induced defect distribution, as suggested by TRIM numerical simulations. On the other hand, elemental depth profiling of implanted species is usually accomplished by means of Secondary Ion Mass Spectrometry (SIMS), but detection of hydrogen suffers of limitations due to the low secondary ion yield and high contamination levels, which make difficult the detection of the species below 10¹⁸ at/cm³. In addition, dynamic-SIMS analysis becomes challenging when probing deep implants because of instrumental artifacts, such as the so-called crater edge effect. For these reasons, SIMS depth profiling of low/medium dose proton implants is not always feasable and requires a careful optimization of instrumental parameters.

In this study, 8" P-type FZ silicon substrates are implanted with protons in the range 400-1200 KeV at various doses, and hydrogen concentration profiles - beyond 20 μm in-depth - are measured by SIMS with high sensitivity over a wide dynamic range. Successful determination of hydrogen with detection limits down to 10¹⁶ at/cm³ in optimized operating conditions is here demonstrated, and optimization procedure is described in detail. The results are compared with post-annealing SRP electrical profiles and TRIM simulations. A discriminating comparison between single and multiple implants is also discussed. Finally, a measurement strategy to standardize implant conditions and to define an in-line monitoring protocol - important to guarantee repeatability of electrical device performances - is proposed.

Nano-porous oxides on Al, as well as on other important metals and its alloys such as Ti or Zr, continuously receive an interest from many branches of nanotechnology, batteries and supercapacitors industry, and in corrosion science. The ultimate goal is to form a tailored highly ordered nano-porous oxide film on a large scale by electrochemical methods, much cheaper than photolithography. Thus, understanding interdependencies and mastering the parameters leading to formation of highly order porosity is a key to achieve it. A number of articles have been published that have provided new insights into the mechanism of formation of porous anodic oxide films on aluminum [i.e. 1,2]. In plain view, an idealized film consists of close-packed hexagonal cells of anodic alumina, with each cell containing a pore at its center. A thin, non-porous, barrier layer is located at the base of the film, where a high electric field is present that results in ionic transport in the alumina, thus enabling formation of the film. The film is formed due to inward migration of oxygen and outward migration of Al under the electric field above the critical value allowing the transport and, most likely, plasticization and flow of the alumina under the mechanical stress.

The exact mechanism of the alumina formation during the anodizing process is not fully understood yet, with very little work done on the movements of oxygen or hydrogen, which is also present in the film. Our study utilized tracer ¹⁸O to scrutinize the porosity formation process and surface analysis methods sensitive to oxygen isotopes. A comparison was made between plasma profiling time-of-flight mass spectrometry (PP-TOFMS), nuclear reaction analysis (NRA) Narrow Resonance Depth Profilling (NRDP) and (Time of Flight Secondary Ion Mass Spectrometry) ToF-SIMS of ¹⁸O tracer in alumina. The findings from ToF-SIMS and PP-TOFMS reveal a partitioning of the tracer between the surface regions and buried layers of the films, in agreement with the NRDP. It demonstrated a level of complementarity of Tof-SIMS PP-TOFMS and potentially becoming a faster method for ¹⁸O depth profiling than NRDP.

[1] Baron-Wiechec A., Burke M.G., Hashimoto T., Liu H., Skeldon P., Thompson G.E., Ganem J.-J., Vickridge I.C.,Tracer study of pore initiation in anodic alumina formed in phosphoric acid, Electrochimica Acta 2013, 113, 302–312,

[2] Baron-Wiechec A., Skeldon P., Ganem J.-J., Vickridge I.C., Thompson G.E., Porous anodic alumina growth in borax electrolyte, Journal of Electrochemical Society 2012, 159, C583-C589

By observing ancient statues with optical microscopy or XRF, traces of coloured pigments can be revealed, mostly in areas best protected from the weathering (gaps, dimples) [1]. Organic materials associated to these colours can be binders for pigments, or coatings applied to the painted statues to protect them from the environment. A particular coating technique, called “ganosis” is described both in Greek and Latin sources (such as Plutarch, Pliny the Elder or Vitruvius writings). A saponified emulsion of beeswax is prepared by boiling it in sea water in presence of a sodium carbonate, natrium, (hydrated Na₂CO₃). It is then mixed with oil and applied on the statue surface, before being heated and polished with beeswax. This specific finishing application process could have had a ritual importance and there is little solid material evidence of such wax use on ancient marble statues.

A colossal Roman marble head from the 2^nd-3^rd century presenting polychromy remains was excavated in 1927 in the Roman theatre of Dougga (Tunisia) and its size suggests it was standing outside. Two cross-sections taken from the face to investigate the superficial layers were analysed using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). On millimetric flat surfaces, TOF-SIMS can provide high spatial resolution ion images (down to 400 µm) of both organic and inorganic compounds, combined with high mass resolution [2]. The imaging abilities of the technique proved suitable to study samples from historical or archaeological objects, such as Renaissance paintings, which are often multi-layered heterogeneous organic-inorganic materials, having interacted in uncontrolled environments for centuries [3]. Combining TOF-SIMS data with a deep knowledge of the historical context, sources, recipes, and materials, as well as their behaviour over time, can inform about the ingredients used when the object was fabricated.

The organic and inorganic compounds were characterized in the pigmented layers and in the two superficial layers above it in the cross-sections. Both contain beeswax, and the ions detected in the deepest of both superficial layers could be associated to beeswax modified with natrium [4]. This result relied on the comparison with reference spectra of beeswax, sodium carbonate and saponified waxes. TOF-SIMS imaging of the stratigraphy in polychromy remains showed a multi-layered application of different waxes matching well with the recipes of “ganosis” from ancient sources. This shows that TOF-SIMS imaging has a good potential in exploring superficial structures found on ancient surfaces of cultural importance.

References

[1] E. Neri, et al. Archaeol Anthropol Sci, 14 (2022), 118.

[2] Q. P. Vanbellingen, et al. Rapid Commun. Mass Spectrom. 29 (2015), 1187–1195.

[3] C. Bouvier, et al. J Mass Spectrom. 57(1) (2022), e4803.

[4] E. Neri, C. Bouvier, et al. J. Cult. Herit. 51 (2021), 29-36.

The wreck of the Mary Rose, the flagship of Henry VIII's fleet, was recovered from the Solent in 1982. In order to preserve this artefact from further deterioration, various methods were employed such as seawater, soft water and polyethylene glycol (PEG) sprays (with three different molecular weights of PEG) as well as antibacterial coatings. Such treatments were used in order to retain the mechanical integrity of the wreck as well as preserving the recovered wood from further damage. However it is unclear as to which depth the PEG has reached within the planks of the hull of the ship, as well as what damage the polymer itself has undergone in the years since the treatment was stopped.

Investigations were conducted using cores extracted from the hull of the Mary Rose. Cylindrical samples (ca. 6 mm in diameter) were sectionned into pieces of approximately 4mm thickness and analysed using ToF-SIMS (Surrey) and by OrbiSIMS (Nottingham). Straighforward inspection of the data as well as semiquantitative approaches together with chemometrics (simsMVA) methods were used for interpretation and analysis of the spectra.

Initial analysis indicated that the PEG had reached a depth of around 14mm but the subsequent OrbiSIMS data also show that the PEG of Mw = 2000 has reached a depth of 20mm, having already undergone degradation within the ten years since the treatment was completed. Indeed, chain scission is observed, in some cases, with a loss of two repeat units and spectra consistent with those obtained from an oxidative degradation mechanism.

Another aspect of the chemistry of the cores was also examined by ToF-SIMS, relating the presence of inorganic ions indicative of salt and/or wash water, with penetration of the water into the wood of the Mary Rose, as well as damage of the wood itself.

It is anticipated that this work will lead to a better understanding of the conservation process and an improved development of the preservation routines to ensure the Mary Rose and other artefacts of similar significance survive for future generations.

Hot particles are microscopic particles deriving from nuclear fuel that have contaminated the environment in accident scenarios such as Chornobyl and Fukushima. The sensitivity and spatial resolution of secondary ionization mass spectrometry (SIMS), makes it well suited to characterizing microscopic fragments of nuclear material [1]. However, isobaric interferences deriving from these complex materials pose significant barriers to their assessment in nuclear forensics and radioecology. Untreated environmental samples yield mass spectra particularly crowded due to many organic compounds on top of isobars in the actinides: ²³⁸U:²³⁸Pu and ²⁴¹Pu:²⁴¹Am, as well as in the fission products: ¹³⁵Cs:¹³⁵Ba and ¹³⁷Cs:¹³⁷Ba [2]. This problem is circumvented by applying resonance ionisation, i.e. selective laser ionization to target single elements and suppress the isobaric interferences typically found in mass spectrometry.

In this work [3], two specialized instruments, combining SIMS and RIMS, were used to analyse single hot particles from Chornobyl: SIRIUS at the IRS in Hannover, Germany, and LION at LLNL in Livermore, USA. Results from multiple particles are presented with interpretations of isotope ratios in U, Pu, Cs, Rb, Sr and Ba.

[1] Fallon, C.M., et al., 2020. ACS Omega 5 (296–303), 1.

[2] Morooka, K., et al., 2021. Sci Total Environ 773, 6.

[3] van Eerten, D.E., et al., 2023. J Haz Mat 452, 131338.

The characterization of complex mixtures is a difficult issue in analytical chemistry. Taking the analysis of active ingredients in plant medicine Scutellariae Radixas (SR) an example, the pharmacopoeia of many countries stipulates that baicalin, the main effective ingredient of SR, shall be quantitatively analyzed by HPLC, and the quality control content shall not be less than 9%, and it is concluded that its primordial form is baicalin. However, the carbonyl peak (about 1725cm-1) of glucuronic acid in baicalin did not appear when the SR was analyzed by infrared spectrum, but its spectrum was similar to that of baicalin magnesium, indicating that the primordial form of baicalin in SR was probably baicalin magnesium. In this study, In order to confirm the primordial form of baicalin in SR, Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), combined with Plasma Emission Spectrometry (ICP-OES) and Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-TOF) and other analytical technology, was used to detect and analyze SR samples, baicalin standard samples and baicalin magnesium standard samples, and accordingly characterized the primordial form of baicalin in SR. The results of this study support the viewpoint that the primordial form of baicalin, the main effective component of SR, is baicalin magnesium.

Supramolecular hydrogel formulations have the potential to increase topical delivery of active agents and are well suited being biocompatible, with facile gel formation from cationic surfactant bis-imidazolium salts and combination with anionic, cationic or neutral drugs [Limón et. al., Eur J Pharm Biopharm, 2015]. Although the potential of hydrogels for improved topical skin permeation analysis has been demonstrated using time of flight secondary ion mass spectrometry (ToF-SIMS) [Starr et. al., Int. J. Pharm, 2019], the chemistry of the systems themselves have not been chemically characterised in their native state. This is primarily due to ion beam induced fragmentation and limitations of mass resolving power, as well as the obscuring of the spectra of frozen hydrated samples with water fragment ions.

In this work we investigate the application of cryo-OrbiSIMS in the molecular characterisation of supramolecular hydrogels loaded with two different porphyrins (0.1% w/v). Skin permeation studies were performed to evaluate the delivery of 5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin (TPPOH) and 5,10,15,20-Tetrakis(4-carboxylatephenyl)porphyrin (TCPP). It was observed that in ex vivo porcine skin permeation studies the TPPOH appeared to have permeated the skin whereas the TCPP had not. Gel monomer skin permeation was below detectable levels in all cases. In order to understand this difference in delivery, cryo-OrbiSIMS and SEM were performed to determine if there were any variations in the physicochemical properties of the gels.

In native state gels as well as those loaded with porphyrin, the cryo-OrbiSIMS spectra show the detection of a range of secondary ions attributable to the gel, [M-H]+ (m/z 901), TPPOH, [M-4H]+ at m/z 677, and TCPP [M-4Na]^- at m/z 788. Ions detected include molecular and fragments ions. The data suggests that the chemistry of the supramolecular gel is confirmed and that the porphyrins have been successfully loaded into the gels and are uniformly distributed. Using a controlled sample sublimation approach to expose the fibrous microstructure of the frozen hydrated gels, cryo-SEM images indicate structural differences between gels with and without porphyrins, with longer, more interconnected fibres present in gels systems without porphyrins. However, the two porphyrin containing systems are comparable, as such the release behaviour is proposed to relate to a difference in their affinity to the gel fibres.

References:

D. Limón, E. Amirthalingam, M. Rodrigues, L. Halbaut, B. Andrade, M. L. Garduño-Ramírez, D. B. Amabilino, L. Pérez-García, A. C. Calpena, European Journal of Pharmaceutics and Biopharmaceutics, (2015), 96, 421-436.

N J. Starr, K. Abdul Hamid, J. Wibawa, I. Marlow, M. Bell, L. Pérez-García, D. A. Barrett, D. J. Scurr, International Journal of Pharmaceutics, (2019), 536, 21-29.

Gathering a substantial understanding of the molecular composition of a complex biological system is often a tedious task. Achieving this goal frequently requires the use of multiple characterization techniques and experiments, each collecting a small portion of the global information. When following such workflows, researchers have to tackle the inherent complexity of puzzling together this fragmented information in order to extract its biological meaning.

Although an ideal investigation technique yielding the totality of the information about a given system in one experiment is yet to be invented, the field of materials science has been consistent over the last decades in providing biological and medical research with useful investigation techniques. Among these, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) has proved particularly successful in characterizing the molecular composition of a wide range of biological systems. Indeed, one single ToF-SIMS acquisition yields detailed molecular maps of the sample composition, with a lateral resolution reaching the 50 nm range for state-of-the-art instruments. When applied to the study of a biological system like a tissue cross section, this methodology allows the simultaneous detection of molecular fragments of a size up to that of lipids with very minimal sample alteration. Because the maximum size of molecular fragments generated in ToF-SIMS only reaches a few thousand atomic mass units, the technique is however less adapted to the specific identification of proteins in such systems.

In this work, we applied ToF-SIMS to the investigation of in vitro epidermal model cross sections¹ and were able to successfully map the distribution of numerous endogenous molecules involved in the epidermal barrier function². Moreover, we report the design of metallic nanoparticle-conjugated antibody probes destined for the specific labelling and detection of proteins in tissue cross sections using ToF-SIMS. Finally, we discuss the process of indirect immunolabelling of epidermal proteins using these metallic probes and their detection in ToF-SIMS thanks to low energy sample etching.

References

1. De Vuyst, E., Charlier, C., Giltaire, S., De Glas, V., de Rouvroit, C.L., Poumay, Y. (2013). Reconstruction of Normal and Pathological Human Epidermis on Polycarbonate Filter. In: Turksen, K. (eds) Epidermal Cells. Methods in Molecular Biology, vol 1195. Springer, New York, NY. https://doi.org/10.1007/7651_2013_40
2. Delvaux X., Noël C., Poumay Y., Houssiau L. (2023). Probing the human epidermis by combining ToF-SIMS and multivariate analysis. Biointerphases 18, 011002. https://doi.org/10.1116/6.0002289

The proof-of-concept of the transfer of fragile biomolecules from a target reservoir to a collector substrate using large Ar gas cluster ion beams (Ar_n⁺-GCIB) was recently demonstrated in our laboratory [1]. For instance, biomolecules as large as 14 kDa (lysozymes) could be transferred intact and with retention of their bioactivity.

Currently, properties such as deposition thickness and bioactivity can be controlled very precisely because they are linearly proportional to the total Ar_n⁺ ion dose used to bombard the reservoir [2]. Moreover, because no solvent is used, separate layers can be built on any collector substrate (e.g. paper, PET, silicon, gold, ect.). Therefore, the construction of new biomaterials such as “thick” multilayers has become possible.

With these advances, the work can now move towards applications. For example, molecular transfer can be used to increase ToF-SIMS sensitivity for molecules in tissues. In this approach, Ar_n⁺-GCIB is used to expand a microvolume from the sample to a collector, which is a material ideally enhancing the ionization yield. The collector is then analyzed using a liquid metal ion gun (LMIG). By doing so, the ion signal is increased by 4 orders of magnitude when pure phosphatidylcholine (PC) is expanded using 10 keV Ar₃₀₀₀⁺ and Ar₅₀₀₀⁺ on a sublimated layer of α-cyano-4-hydroxycinnamic (CHCA). This matrix-assisted laser desorption/ionization (MALDI) matrix was selected as the best candidate amongst a pattern of different matrices. The transfer of PC from the grey matter of a mouse brain was also achieved on different materials (e.g. MALDI matrices, Polyethylene, Si and Au) with varying degrees of success.

References

[1] V. Delmez, H. Degand, C. Poleunis, K. Moshkunov, M. Chundak, C. Dupont-Gillain, A. Delcorte, J. Phys. Chem. Lett. 12 (2021) 952–957.

[2] V. Delmez, B. Tomasetti, T. Daphnis, C. Poleunis, C. Lauzin, C. Dupont-Gillain, A. Delcorte, ACS Appl. Bio Mater. 5 (2022) 3180–3192

The potential energy landscape of mobile ions in solid-state materials and the atomic scale structure are intimately interrelated. This interrelation and the resultant properties, e.g. the mobility of the ions, is of paramount interest in contemporary material science with direct applications in energy storage and conversion. Understanding the interplay of structure, energy landscape and ionic transport of ionic solids is of crucial importance for a knowledge based development of improved and new functionalities of these materials.

Here we demonstrate for the first time combined experimental and theoretical efforts in quantifying such landscapes and its resulting transport function. We describe the results of unique transport experiments, where native mobile Lithium ions in a Lithium Borate glass are depleted and replaced unidirectionally by foreign alkali ions M⁺ = K⁺, Rb⁺ and Cs⁺ in a charge attachment induced transport (CAIT) experiment. The resulting depletion/replacement profiles extend down to several hundred nm into the material as measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS) resembling time-dependent macroscopic transport with characteristic transport coefficients. The experimental data reveal that most of the native Lithium ions are indeed mobile but a fraction of several percent of the ions appears to be immobile.

In order to understand and rationalize these experimental findings a combination of both macroscopic and microscopic transport theories is employed. The macroscopic approach is based on the frame work of the Nernst-Planck-Poisson theory focusing on the time dependent macroscopic flux of ion density on a spatial grid with effective diffusion coefficients. The microscopic approach on the other hand is based on the hopping of native and foreign ions in the potential energy landscape of the material for specific concentration ratios reflecting time slices of the experiment.

Both macroscopic and microscopic approach unanimously reveal that the diffusion coefficient of the native mobile Lithium ions decreases by approximately 3 orders of magnitude as the molar fraction of the Lithium is decreased from 1 to 0.2 (the molar fraction of the foreign ion increases concomitantly). Both approaches correctly predict that a finite fraction of the native Lithium ions is effectively immobile because the diffusion coefficient of some native Lithium ions becomes significantly smaller than that of the foreign alkali ions, in which case the concentration profiles exhibits a time-independent plateau. The key to the successful description is the combination of a concentration dependent Fermi energy in the macroscopic approach with the concept of an element specific and concentration dependent miss match in the microscopic approach.

The combination of a CAIT / ToF-SIMS experiment with macroscopic and microscopic transport theories addresses the old challenge of bridging the understanding from the hopping in the local structural landscape all the way to long range DC transport as relevant for technical applications. Progress along this line is being presented. Still, important questions remain to be tackled in the future, but the road map to a new level of understanding transport in ion conducting solids has now been laid out.

Metal-oxide (MO) surfaces have successfully been modified to elicit specific responses attributed to either structural variations and/or chemical functionality. Structural modification of a bulk surface is achieved by exploiting the combined effects of top-down and bottom approaches during electrochemical anodization (EA). Imparting nanoscale geometries has reportedly improved biointegration as a result of structural similarities to corresponding biological environments namely, the extracellular matrix.^[1] Additionally, an influence on surface reactivity due to chemical variations has also been observed.^[2] In this context, nanostructured bulk surfaces are highly relevant as hybrid materials, that are capable of eliciting multi-functional responses. This work describes the use of EA to fabricate MO nanotubular layers that are isolated from the parent substrate and made available for deposition onto bulk ceramic. Herein a free-floating zirconia nanotubular layer is deposited onto a bulk zirconia ceramic preform in an acetone bath.^[3] These nanostructures can further be modified via facile application of self-assembled monolayers (SAM) to subsequently seal or ‘cap’ the nanotube mouths^[4] making them ideal for triggered release applications in the biomedical field. Such bulk surfaces modified with nanotubes may be used to store drugs or therapeutics that can selectively release under appropriate conditions as this hybrid assembly can readily transform static bulk surfaces to those capable of dynamic elution from the overlying nanotubular reservoirs. The hybrid material was thoroughly characterized using scanning electron microscopy (SEM), ToF-SIMS, water contact angle measurements (WCA) etc. Such nanotubular reservoirs developed on the implant surface would be capable of facilitating ‘smart’ developmental strategies towards controlled multi-drug release models that can even elicit sequential release of drugs to limit clotting, inhibit infection and ultimately promote healing.

REFERENCES

[1] R. Junker, A. Dimakis, M. Thoneick, J.A. Jansen, Effects of implant surface coatings and composition on bone integration: A systematic review, Clin. Oral Implants Res. (2009). https://doi.org/10.1111/j.1600-0501.2009.01777.x.

[2] S.N. Vakamulla Raghu, M.S. Killian, Wetting behavior of zirconia nanotubes, RSC Adv. 11 (2021) 29585–29589. https://doi.org/10.1039/D1RA04751E.

[3] S.N.V. Raghu, P. Hartwich, A. Patalas, M. Marczweski, R. Talar, C. Pritzel, M.S. Killian, Nanodentistry aspects explored towards nanostructured ZrO2: Immobilizing zirconium-oxide nanotube coatings onto zirconia ceramic implant surfaces, Open Ceram. (2023) 100340. https://doi.org/10.1016/J.OCERAM.2023.100340.

[4] S.N.V. Raghu, G. Onyenso, S. Mohajernia, M.S. Killian, Functionalization strategies to facilitate multi-depth, multi-molecule modifications of nanostructured oxides for triggered release applications, Surf. Sci. 719 (2022) 122024. https://doi.org/10.1016/j.susc.2022.122024.

OrbiSIMS is a secondary ion mass spectrometer with dual mass analysers; a time of flight mass spectrometer for high-speed imaging and an Orbitrap for high mass resolving power and mass accuracy. It was originally designed for biological imaging but the dual analyser configuration combined with multiple ion beams for analysis has proved to be useful for a wide range of analytical measurements from identification of deposits on fuel injectors to organic electronics [1-4]. More recently, there has been interest in the application to semiconductor materials using the Orbitrap to resolve peak interferences that obfuscate analysis in depth profiling experiments [5]. An Sb delta layer in silicon sample was used to determine the depth resolution and optimise parameters and an Sb implant in silicon sample was used to measure the useful yield. The depth resolution and useful yield performance were compared with a magnetic sector instrument (SC Ultra, CAMECA, France) and time-of-flight instruments (IONTOF, Germany) typically used in the semiconductor industry. Each instrument type has advantages and disadvantages, which are discussed. Guidance is provided for analysts using OrbiSIMS for semiconductor analysis.

1. M. K. Passarelli. et al, I. S. Gilmore, Nat. Methods, 14(2017)12, 1175-1183.

2. C. L. Newell, et al, A. P. Gould, Angew. Chem, 59(2020)41, 18194-18200.

3. J. Zhang, et al, I. S. Gilmore, P. D. Rakowska, Anal. Chem. 92(2020)13, 9008-9015.

4. S. Sul, G. Trindade, J. Kim et al , https://www.researchsquare.com/article/rs-1279729/v1 (2022).

5. A. Franquet, et al., Vacuum 202(2022)4, 111182.

Sub-nanometer thin film surface modifications have emerged as a promising technique to enhance the performance and stability of mixed ionic electronic conducting (MIEC) materials, such as the perovskite La_0.6Sr_0.4CoO_3-δ (LSC), particularly in terms of oxygen exchange kinetics and degradation resistance. However, the underlying interaction mechanism between these decorative layers and MIEC materials remains largely speculative, forming the basis of ongoing research endeavors.

By employing a novel ToF-SIMS approach, this research provides valuable insights into the complex interplay between LSC and sub-nm oxidic decorations. Even less than one monolayer of each oxide decoration exhibited discernible differences in the interaction with LSC, as evidenced by alterations in the secondary ion (SI) signal during analysis. Moreover, experiments revealed noticeable stoichiometric distortions of the charge carriers within the LSC, indicating a competitive relationship for lattice sites within the LSC perovskite.

The results shed light on the underlying electronic-chemical interactions, demonstrating the significance of variations in the oxide thickness. These findings contribute to the ongoing efforts to optimize the design and fabrication of MIEC materials for enhanced oxygen exchange kinetics and improved stability, paving the way for potential advancements in various energy-related applications.

Surface analysis techniques such as tandem (MS/MS) time-of-flight mass spectrometry and X-ray photoelectron spectroscopy (XPS) are used to identify and understand the distribution and mode of binding of corrosion inhibitors on the metal surface. A corrosion inhibitor is a chemical compound added in a very small amount to a corrosion medium. When a metallic material is immersed in a corrosive medium, the corrosion inhibitor mitigates corrosion by adsorbing onto the metal surface. A gas cluster ion beam (GCIB) sputtering source is a very suitable technique for analyzing thin organic coatings without chemically altering their composition. In this work, the surface layer of a self-assembled corrosion inhibitor on a metal surface was analyzed. The conformation was determined using MS/MS ToF-SIMS, a rare technique in the SIMS database. GCIB sputtering and 3D ToF-SIMS imaging were used for 3D distribution analysis. The analysis showed that the chloride was located under the surface layer of the corrosion inhibitor. This finding was confirmed by GCIB-XPS analysis using Ar cluster beam sputtering at different acceleration energies and cluster sizes.

To enable the use of a high-capacity Li-metal anode in All-Solid-State-Batteries (ASSBs), the stability of the Solid-Electrolyte (SE) against Li-metal is crucial for the development of next generation batteries. Besides commonly used characterization techniques such as X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS), secondary ion mass spectrometry (SIMS) presents itself with its high sensitivity, lateral resolution and 3D elemental mapping as a valuable tool for deconvoluting the characteristics of the buried Li/SE interface. The reactivity of Li-metal imposes additional challenges for the experimental setup, which calls for the development of advanced analytical techniques.¹

First established by Wenzel et al.², in-situ deposition of Li-metal onto the SE via sputtering of a Li-metal target, followed by XPS analysis, elucidates the stability of the Li/SE interface upon contact. A similar approach was later used within a SIMS instrument: Otto et al.³ investigated the stability and microstructure of the interface between Li metal and different inorganic SEs. The development of a designated preparation chamber with an attached effusion cell enabled the in-situ deposition of Li-metal onto the SE.

Following a similar setup to Otto et al.³, this study extends the in-situ characterization of the Li/SE-interface to Solid Polymer Electrolytes (SPEs). Compared to their rigid inorganic counterparts, flexible SPEs maintain better contact to the electrode, which reduces dendrite growth and contact resistance.⁴ While the employment of SPEs in ASSBs is widely studied, the elusive Li/SPE-Interface is yet to be characterized.

Herein, we present an in-situ TOF-SIMS study of said interface to shed light on its microstructure, stability, and chemical composition. Using a newly developed preparation chamber, Li-metal is in-situ deposited onto SPEs and the forming interface is analyzed. Comparing other Li-deposition methods, evaluating the evolution of the interface over time, and characterizing its composition, yields a systematic investigation of the stability of the Li/SPE-interface.

Using MgO as a reference substrate, we establish a reliable routine to deposit Li-metal with a low temperature effusion cell. Li-deposition on SPEs and subsequent depth-profiling reveals differences in stability and chemical composition of the Li/SPE-interface. To unveil the relevant signals within the various polymer fragments, the data are evaluated via statistical methods such as principal component analysis (PCA).

This presentation outlines the first application of our new designated preparation chamber for the in-situ deposition of Li-metal on SPEs and summarizes the experimental set-up, which ultimately enabled us to characterize the Li/SPE-Interface.

References

1. Banerjee, A., Wang, X., Fang, C., Wu, E. A. & Meng, Y. S. Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes. Chemical Reviews 120, 6878–6933; 10.1021/acs.chemrev.0c00101 (2020).

2. Wenzel, S. et al. Direct Observation of the Interfacial Instability of the Fast Ionic Conductor Li 10 GeP 2 S 12 at the Lithium Metal Anode. Chem. Mater. 28, 2400–2407; 10.1021/acs.chemmater.6b00610 (2016).

3. Otto, S.-K. et al. In Situ Investigation of Lithium Metal–Solid Electrolyte Anode Interfaces with ToF‐SIMS. Adv Materials Inter 9, 2102387; 10.1002/admi.202102387 (2022).

4. Ding, P. et al. Polymer electrolytes and interfaces in solid-state lithium metal batteries. Materials Today 51, 449–474; 10.1016/j.mattod.2021.08.005 (2021).

The application of low and high energy ion beam techniques has played a pivotal role in Lebanon for over a decade, enabling the identification of fraudulent practices employed in Lebanese currency, as well as essential products like food and pharmaceutical drugs.

In this study, we present an innovative approach utilizing the Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) technique to address specific inquiries posed by the counterfeiting combating section of the central bank of Lebanon. The primary objectives were to determine the types of materials employed in the production of counterfeit 1k and 5k Lebanese Lira (L.L.) secure stripes, the printing processes involved in counterfeiting the highest denomination, 100k L.L., and the identification of the UV ink used in the forgery of this banknote. Based on the 3D analysis with the Ar source, our analysis revealed compelling evidence suggesting that the counterfeit stripes found on the 1k and 5k L.L. banknotes were most likely made from aluminum gift papers. Furthermore, our investigation demonstrated that the individuals behind the counterfeiting operation possessed a deep understanding of the genuine banknote production process, as the layer printing technique employed in the fake 100k L.L. banknotes closely mirrored that of the authentic ones. Regarding the identification of the UV ink used in the counterfeiting process, our findings indicated that the ink utilized in the fake 100k L.L. banknotes was a commercially online available variant.

The outcomes of this investigation unveil the counterfeit techniques employed and contribute to enhancing law enforcement's ability to combat financial fraud and safeguard the integrity of Lebanese currency.

Introduction:

The organic matter contained in primitive meteorites called chondrites, is a witness to the early stages of formation of the Solar System. Better characterizing it and understanding the way it interacted with mineral phases and the extent, to which it evolved under secondary processes within the parent asteroid, are critical issues in astrochemistry. In this work, we present the study of two differently aqueously altered CM chondrites, Cold Bokkeveld [1] and Paris [2,3], together with an ordinary LL5 chondrite, Tuxtuac [4] used as a control sample. The aim of this study is to understand the effect of parent body hydrothermal processes on the organic matter structure, composition and localization within the mineral matrix. Thus, all the samples were analyzed without any chemical extraction by TOF-SIMS [5] with a specific focus on comparing and localizing organic signatures.

Materials and methods:

Freshly cut millimetric fragments of the three meteorites were analyzed using a TOF-SIMS V spectrometer. Areas of 500µm*500µm were analyzed using 30keV Bi₃⁺ clusters emitted from a LMIG nanoprobe (0.3pA) and focused to 5µm, diameter spot. Cleaning with argon clusters was performed systematically prior to the analyses according to an established previous protocol [5]. We also analyzed in the same conditions a set of “CHO” and “CHON” films produced in laboratory, in order to help for the interpretation of the macromolecular signatures.

Results and discussion:

The organic matter contained in these primitive samples is composed of very complex mixtures of a large diversity of molecules and macromolecules randomly structured and highly cross-linked [6,7]. At masses lower than 150u, the three meteorites have undistinguishable organic matter average signatures. At higher masses, while organic matter signatures exhibit large and multiple peaks at each mass unit that corroborate their very complex and random structure, the characteristic signatures differ slightly from one sample to another and seem to indicate that the hydrothermal process tend to increase the oxygen content and the unsaturation degree of the organic matter. This latter increase would be consistent with a previous study that found an increase of the aromaticity degree with aqueous alteration [8].

Another finding that will be discussed is related to organo-iron and organo-silicon features. Both were found in the samples and confirm a previous result on the Paris meteorite [5], whereas no organo-magnesium nor any other organo-alkali feature was found. This result emphasizes the particularly strong interaction that must be present between the chondrite silicates and especially the iron-rich phyllosilicates, and the organic matter. Finally, we will discuss the localization of alkalis in both CMs and their relation to salts, organic salts included.

[1]Rubin A. et al. (2007)Geochimica et Cosmochimica, A71(9), 2364-2382

[2]Hewins R.H. et al. (2014)Geochimica et Cosmochimica, A124, 190-222

[3]Marrochi Y. et al. (2014)Meteoritics&Planet. Sci., 49(7), 1232-1249

[4]Graham A. L et al. (1988)Meteoritics, 23: 321

[5]Noun M. et al. (2019 Life, 9(2), 44

[6]Alexander C.M.O.D. et al. (2017)Chemie der Erde/Geochemistry, 77 227

[7]Botta, O. & Bada, J. L. (2002)Surveys in Geophysics, 23, 411

[8]Alexander C.M.O.D. et al. (2014)Meteoritics&Planet. Sci., 49(4), 503-52

The alkali-silica-reaction (ASR) and the resulting damage mechanism are a major problem for the durability of concrete, causing millions of dollars of damage annually. Affected are structures that come into contact with water and thus a large part of the global infrastructure such as roads, runways, bridges and railroad sleepers. The cause of a damaging ASR is the swelling alkali silica gel, which results from the reaction of alkali ions of the pore solution with reactive silicates from the aggregate. While numerous factors such as the influence of moisture, temperature, alkali content of concrete, and the role of admixtures have been intensively investigated, important questions regarding the role of specific dissolved ions in the pore solution are still unresolved. In this context, aluminum ions are of particular interest due to their potential to prevent a deleterious ASR.

The overall goal of this research project is to understand the influence of an aluminum containing passivating layer on the ASR reaction and its damage mechanism in detail. The focus lies on the characterization of the surface layer formation in dependence of various parameters, for example the silicate surface it forms on, temperature, time, and the concentration of aluminum in the solutions.

Depth profiling time-of-flight secondary ion mass spectrometry (ToF SIMS) and X-ray photon spectroscopy (XPS) investigations were carried out on different silicate samples (e.g. quartz glass) that had been stored in sodium hydroxide solutions in the presence or absence of aluminum ions. These comparative studies revealed that alumina was enriched in the near-surface region. Moreover, slightly higher values were detected for the photoelectron binding energy of aluminum than expected for Al₂O₃, indicating very small nanoparticles and/or the formation of an aluminosilicate (Published under DOI: 10.1002/sia.6918).

Further work is dedicated to a transfer the knowledge gathered with model compounds to different silicate rocks prone to ASR reactions. Here, the influence of foreign ions from the minerals is expected to alter the reaction mechanism.

Macro-autophagy, hereafter referred to as autophagy, is an evolutionary conversed degradation process that removes unnecessary and dysfunctional cytosolic components through the lysosome pathway. In this way, autophagy guards against metabolic fluctuations by supplying cells with amino acids during periods of stress, and maintains cytoplasmic function by removing old and dysfunctional proteins and organelles. Dysregulation of autophagy has been linked to the progression of pathologies, most notably neurodegenerative diseases where the decrease of autophagy activity leads to the accumulation of toxic proteins. This protein accumulation reflects the disturbed cellular proteome. Rapamycin, a drug known as an autophagy inducer via the mTOR pathway, has been shown to convey positive effects on diseases in both cell and animal models. However, the underlying molecular mechanism of autophagy towards pathologies and the rescuing effects of rapamycin have not been fully understood. The combination of NanoSIMS and confocal fluorescence microscopy provides a powerful tool to investigate these molecular connections at a subcellular level.

This project aims to study the molecular relation between autophagosome activity and protein turnover in human neuronal progenitor cells (NPC), obtained from both healthy and Schinzel–Giedion Syndrome (SGS) neurodegenerative patients. This holds great potential in understanding the fundamental role of autophagy in neurodegenerative diseases and developing effective therapies.

Methods. To determine the autophagosome turnover rate, the fusion between autophagosome and lysosome is inhibited using Chloroquine, and then the rate at which autophagosomes accumulate in the cells is determined as a measure of autophagosome turnover. For correlative confocal and NanoSIMS imaging, cells are loaded with ¹⁵N-Leucine for two days followed by a clearing period in regular cell medium. Afterwards, autophagosomes are labelled with fluorescent markers, and the cells are embedded in LR white resin, cut into thin sections, and imaged using confocal microscopy followed by NanoSIMS. These two images will be overlaid using cellular structures that are easily recognized, such as the nucleus and cell borders, allowing locating of individual autophagosomes and their respective protein turnover. In addition, mitochondria are used as a reference for organelle turnover.

Results. Healthy NPC exhibited higher autophagosome turnover and cytosolic/mitochondrial protein turnover compared to SGS highlighting a difference in the dynamic molecular events between healthy and diseased cells, and a possible involvement of autophagy in disease burden. No differences in protein turnover in the nucleus of healthy and SGS cells were observed, owning to autophagy's cytosolic-selective degradation. In addition, ¹⁵N enrichment within the autophagosomes was similar to that in the cytosol regardless of treatment in both cell types. Finally, rapamycin did not affect SGS cytosolic/mitochondria protein turnover, however, the healthy cells showed an unexpected increase in ¹⁵N enrichment despite enhanced autophagosome turnover which may be due to the underlying molecular mechanism of Leucine.

Dye-sensitized solar cells (DSSCs) offer creative design possibilities in terms of shape, color and transparency, and perform relatively better at diffuse light conditions when compared to other solar cell technologies. These differentiating properties make DSSCs an interesting candidate for niche creative applications and building integrated photovoltaics. Recently, DSSCs have been used to introduce the concept of so-called photovoltaic photographs, solar cells wherein images are captured by controlled light-induced patterning, or selective bleaching, of the light-absorbing molecules [1]. The proposed method allows direct integration of high-resolution patterns, such as images, logo's and text, into the photoactive layer of the solar cell, thereby circumventing common issues with traditional patterning methods such as scalability, ease of fabrication, and transferability.

In this study, we examine the underlying light-induced degradation mechanism occurring in ruthenium dye N719, a commonly used dye for high-performance DSSCs, using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) (TOF.SIMS 5 NCS, IONTOF GmbH, Germany. Device located at imec, Leuven - Belgium). A comparison of the mass spectra obtained at bleached and non-bleached areas of the photoanode provides insight into the degradation mechanism. Principle component analysis (PCA) is used to accelerate the identification of discriminating secondary ions. The results suggest that the observed N719 degradation involves a photo-induced oxidation mechanism of the thiocyanate ligands bound to the central ruthenium atom. The results are discussed and an outlook on future work is provided.

[1] J. Hustings et al., Sol. Energy Mater Sol. Cells 246 (2022)

Beams of cluster particles of various sizes and stoichiometric compositions are currently widely used both in SIMS and in numerous other applications of ion technologies [1]. Among the cluster generation methods, ion sputtering [2] has a number of advantages; however, the nature of cluster formation processes during ion bombardment is still largely unclear. The main analytical models of cluster formation under the action of ion bombardment cannot, as a rule, describe the experimental mass distributions of sputtered clusters, which for homogeneous particles, depending on the number of atoms n in them, are described by the power law Y(n)~n^-δ [2], where δ=4÷9 and depends on the sputtering coefficient. Using synergetic concepts, it was shown in [3] that by analysis of the sputtering process by a set of “reactions” of the type where А are surface atoms, X are sputtered atoms, and n and m are integers, one can obtain the distribution the probability of the number of atoms P_S(n) in sputtered cluster, and when the equilibria of these reactions are shifted, P_S(n) has a non-Poisson character in accordance with experiments [1].

To determine the possibility of describing the processes of cluster formation during ion sputtering in the framework of [3], taking into account the combinatorial nature of these processes [4], we performed extensive SIMS studies of the emission and fragmentation in all stoichiometrically possible directions of Si_n⁺, Si_nO_m^±, V_nO_m^± and Nb_nO_m^±± clusters. The experiments were carried out according to a technique similar one used in [5], when Si, V, and Nb targets were sputtered by Xe⁺ beams and O₂ was inletted onto bombarded surfaces.

The volume performed by SIMS studies of the processes of emission and decay of clusters shows that, both for homogeneousr and heterogeneous clusters, the process of their formation under ion sputtering of surfaces can be described in frameworks of synergistic concepts [3]. The combinatorial approach [4] in this case can serve as an effective method for the analysis of quasi-chemical reactions in which certain clusters of a specific size and stoichiometric composition are formed.

[1] Popok V.N., Barke I., Campbell E.E.B., Meiwes-Broer K.-H. //Surf. Sci. Reports. 2011. V.66. P.347-377. https://doi.org/10.1016/j.surfrep.2011.05.002

[2] Wucher A. Sputtering: Experiment. //Matematisk-fysiske Meddelelser. Det Kongelige Danske Videnskabernes Selskab. Copenhagen, 2006. V.52. P.405-432.

[3] Maksimov S.E., Oksengendler B.L., Turaev N.Yu. // Journal of Surface Investigation. 2013. V.7. №2. P.333–338. https://doi.org/10.1134/S1027451013020407

[4] Dzhemilev N.Kh. //Journal of Surface Investigation. 2012. V.6. №4. P.254–258. DOI:10.1134/S1027451012080083

[5] Dzhemilev N.Kh., Kovalenko S.F., et al. //Journal of Surface Investigation. 2017. V.11. № 3. P.490–495. DOI: 10.1134/S1027451017010074

Polyurea thickened greases have gained increasing interest particularly in the lubrication of electric motor bearings, due to its inherent oxidative stability and high operating temperature. However, they can be difficult to manufacture due to the health and safety concerns of the starting materials (isocyanates). Additionally, fully understanding the grease structure is crucial in comprehending and improving the final grease properties. Previous attempts at defining the structure of a grease have largely been via scanning electron microscopy (SEM). However, removal of the base oil component is required prior to analysis, which modifies the true structure. Here, we develop a method for in depth chemical and structural analysis of polyurea grease using a similar protocol employed in the cryo-OrbiSIMS analysis of frozen hydrated biofilms [1]. Emphasis is placed on characterising the grease without distorting the original microstructure, via high pressure freezing, cryogenic SEM (cryo-SEM) and cryogenic orbital trapping secondary ion mass spectrometry (cryo-OrbiSIMS).

Commercially sourced base polyurea grease was investigated, with the potential to extend into the analysis of polyurea grease synthesised via less hazardous chemistries. The results show that the commercial base grease is amenable to high pressure freezing and analysis via cryo-SEM and cryo-OrbiSIMS. Spherical urea particle like structures distributed in the base oil matrix were observed in the cryo-SEM images. This is in agreement with the cryo-OrbiSIMS imaging, where similar shaped distributions of ions corresponding to urea were observed. Such findings provide important insight into understanding the urea particle shape and size required for optimal performance, and to build a methodology for understanding the structure of materials made from safer chemistries.

[1] Zhang, J.; Brown, J.; Scurr, D. J.; Bullen, A.; Maclellan-Gibson, K.; Williams, P.; Alexander, M. R.; Hardie, K. R.; Gilmore, I. S.; Rakowska, P. D. Cryo-OrbiSIMS for 3D Molecular Imaging of a Bacterial Biofilm in Its Native State. Anal. Chem. 2020, 92, 9008– 9015, DOI: 10.1021/acs.analchem.0c01125

Neuronal progenitor cells (NPCs) give rise to glial and neuronal cell types in the brain during human development as well as acting as a reserve in adulthood. Many extra-and intracellular factors are involved in maintaining the NPCs' function and differentiation, and dysregulated composition of lipids in the plasma membrane is therefore connected to altered brain function and morphology, leading to diseases. The altered lipid composition can also reflect disturbances intracellularly. Despite lipids in the plasma membrane being a useful reflection of cellular health and function, they are commonly overlooked in research. A complicating factor is that the conventional bulk analysis methods for studying the plasma membrane lipids often ignore the molecular differences at the single cell level, or other methods lack the ability to explore the native plasma membrane lipid composition specifically. We aimed to characterize the lipids at the NPC plasma membrane using ToF-SIMS imaging, which overcomes these two limitations. We first explored the native NPC plasma membrane followed by studying the lipid turnover of NPCs using different isotopically labelled lipid precursors, including 13C-choline, 13C-linoleic, 13C-stearic, and 13C-lauric acids. Our results indicate that the NPC plasma membrane contains a high abundance of ceramides, phosphatidic acids, phosphatidylcholines, and glycerophosphoserines. Furthermore, different lipid precursors were found incorporated into different molecular membrane lipids, especially comparing between short- and long-carbon chain fatty acid precursors, and between unsaturated and saturated precursors. The current study illustrates the potential of ToF-SIMS to study neuronal lipids providing molecular- and spatial-rich information in single cells.

Batteries are very important to achieve carbon net zero. Understanding battery materials change, electrode surfaces, solid electrolyte interphase (SEI) evolution and novel solid-state electrolyte structures is very helpful for developing better batteries. Surface chemical analysis techniques such as X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy are often used but they have their limitations. XPS analysis cannot always resolve overlapping binding energies for some key SEI elements. The SEI often has poor Raman signal intensity. These are all hurdles for battery applications.

Secondary ion mass spectrometry has great potential to study interfacial chemistry in batteries owing to high sensitivity and high-resolution imaging in 2D and 3D. In this study, we use an OrbiSIMS instrument which is equipped with two complementary mass spectrometers (MS). A time-of-flight (ToF) MS has the capability for 2D and 3D imaging using a Bi₃⁺ liquid metal ion gun with a spatial resolution of up to 200 nm but with modest mass resolving power. The Orbitrap MS offers high mass resolution and mass accuracy (> 240,000 at m/z 200 and < 2 ppm, respectively). The instrument is equipped with low energy Cs and O₂ sputter beams for high resolution depth profiling of inorganic materials. It also has a Leica docking station enabling samples to be transferred using a vacuum sample transfer chamber from an argon glove box without atmospheric exposure. To improve the quality of measurements on battery materials, we have used ion implanted materials to determine relative sensitivity factors for relevant elements. We have also conducted a systematic study to optimise the OrbiSIMS depth profiling capability. These findings along with recommendations to reduce effects of signal saturation will be discussed and examples of the application to batteries will be provided. We will provide examples of the application of ToF MS and Orbitrap MS. (1,2)

1. X. Yao et al., Energy Environ. Sci., 2023, DOI: 10.1039/D2EE04006A.
2. S. Marchesini et al., ACS Appl. Mater. Interfaces, 14(2022)52779-52793.

In order for most biological specimens to be analyzed with ToF-SIMS, either the water must be removed via a process such as freeze-drying or the samples must be frozen and analyzed under cryogenic conditions. Cryogenic preparation and analysis of biological samples preserves the 3-dimensional structure of tissues and biofilms and can prevent migration artifacts that occur during freeze-drying. However, ToF-SIMS analysis of water ice results in a spectrum of ice cluster ions extending to high masses that can interfere with detection of biomolecules. Furthermore, metastable decay of the ice cluster ions in the time-of-flight analyzer can lead to a high background that raises the detection limit for target analytes. In this study, we have investigated the influence of a range of analytical parameters, including primary ion species and cluster size, analysis temperature and time-of-flight analyzer settings on the water ice spectrum. The aim of this work is to optimize analysis conditions in order to improve the detection limit for antibiotic compounds.

Three antibiotic compounds, ciprofloxacin, tetracycline and rifampicin, have been investigated. Each of the three antibiotics was prepared at a concentration of 1 mg/ml in an aqueous solution containing 5% dextran and 150 millimolar ammonium formate. The aqueous solutions were pipetted onto a thin copper mold in a dry argon atmosphere. The copper mold with the solution was then plunge-frozen in liquid propane, cooled further in liquid nitrogen on a copper block and then transferred (without exposure to moist air) into an IONTOF M6 equivalent instrument, which is equipped with an active liquid nitrogen heating/cooling system in both the load-lock and the analysis chamber. Six different primary ion species were studied. These included 30 keV Bi₁⁺, Bi₃⁺ and Bi₅⁺ and 2 keV Ar₁₀₀₀⁺, Ar₁₅₀₀⁺ and Ar₂₀₀₀⁺. In between analysis scans, a GCIB sputter scan (2 kV, 2 nA, Ar₂₀₀₀⁺) was used to create a fresh surface. Measurements were performed in two different analyzer modes, with and without extraction delays. The analysis temperature was varied from -175 °C to -90 °C.

Details of the spectral changes resulting from analysis temperature, primary ion species and size and analyzer settings will be presented. For each of the analysis conditions, the ratio of the antibiotic molecular ion to ice cluster ions was evaluated. A gradual increase in this ratio was observed with increasing temperature until rapid freeze-drying of the sample is observed near -90 °C. Additionally, the ratio of antibiotic molecular ion to water ice ions decreased with increasing bismuth cluster size, but for increasing argon cluster sizes the opposite trend was observed. Using delayed extraction led to an additional increase in the ratio of antibiotic to water ice ions. Based on these results, recommendations for optimal analysis conditions for detection of the antibiotics will be presented.

Electrocatalysis is and will continue to play a central role in the development of a new and modern sustainable economy, especially for chemicals and fuels. The storage of excess electrical energy into chemical energy by splitting water into hydrogen and oxygen is a feasible solution in this economic sector. A major drawback of electrical energy lies in the storage. Therefore, hydrogen is discussed as promising alternative. Fortunately, this issue can be effectively addressed through the implementation of chemical storage mechanisms. Due to their abundance on Earth and inherent stability in alkaline solutions, transition-metal oxides have become one of several viable alternatives to conventional noble-metal catalysts. Since FeNi oxide is one of the most active oxygen evolution reaction (OER) electrocatalysts for alkaline water electrolysis, it has been the subject of extensive research.

A series of different types of FeNi oxide nanoparticles (NPs) with atomic ratios covering a broad range, and various sizes with specific stoichiometric and non-stoichiometric iron and nickel ratios was synthesized and characterized by the combination of surface analysis techniques, such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The morphology was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed the coexistence of mixed and unmixed iron and nickel NPs with comparable sizes in the range of 30–40 nm across all ratios. The synthesis technique displayed control over the iron-nickel ratio, as evidenced by energy dispersive X-ray spectroscopy (EDS) data. The presence of magnetite (Fe₃O₄) was detected in all samples investigated by X-ray diffraction (XRD). Furthermore, the existence of nickel ferrite (NiFe₂O₄) was shown in the Fe₂Ni by XRD analysis. For the cyclic voltammetry (CV) measurements, the NPs were deposited onto glassy carbon electrodes using Nafion^® as an ionomer, and 1 M KOH was employed as the electrolyte. Subsequently, the NPs/Nafion^® electrode was transferred into the ToF-SIMS chamber to allow surface analysis and depth profiling.

The ToF-SIMS analysis revealed distinct peaks corresponding to Fe, Ni, and other peaks associated with Nafion^®, whereas a straightforward correlation between the Ni.Fe ratio and the SIMS peak pattern is not possible.

The catalytic activity towards OER was evaluated through CV measurements, where the Fe₂Ni₃ ratio exhibited the most favorable performance, displaying a lower overpotential.

In the last decade the continuous increase of electric power demand has shifted the attention towards wide band semiconductors (WBG), such as gallium nitride (GaN) and related alloys. An interesting aspect related to GaN materials is the possibility to grow AlGaN/GaN heterostructures with the formation of two-dimensional electron gas (2DEG) and which allows to design AlGaN/GaN high electron mobility transistors (HEMT) structure. A major challenge with this device technology is its normally-ON nature which limits their applications. To improve system reliability, normally OFF HEMTs are highly desirable. One method to achieve this goal is to grow a p-type cap layer (pGaN). The most used acceptor is Mg, having a relatively large ionization energy that has been estimated to be in the range 0.12–0.16 eV, depending on the doping level.[1] Mg-doped GaN is grown by metalorganic vapor deposition - MOCVD with metalorganics and organic compounds and hydrides as precursors (ammonia NH₃,Trimethylgallium - TMGa and biscyclopentadienyl-magnesium - Cp₂Mg), and the growth usually is in H₂ ambient. The consequence is the presence of Mg-H and atomic H which dramatically increases the resistance of Mg-doped GaN [2]. Upon implantation, Mg impurities have to be activated and this is obtained by thermal annealing which induces hydrogen dissociation from the Mg–H complex in the Mg-doped GaN layers. Despite the mechanism is known, there have been only a few quantitative experimental investigations on the relationship between the amount of hydrogen dissociated from Mg-doped GaN and the electronic properties of the p-GaN.

The aim of this study is to correlate the role of hydrogen in the thermal activation process of Mg-doped GaN and the resistivity variation of p-GaN as a function of the temperature up to 800°C. ToF-SIMS was used to evaluate the Mg and H depth profiles [3]. Hall measurements were adopted to investigate the conductive properties of the annealed samples. The sample analyzed are stacks with 100 nm of pGaN, a thin AlGaN layer (around 20nm), grown on GaN buffer layer. H quantification by ToF SIMS on typical GaN/AlGaN structures is tricky since hydrogen is present as a spurious element in the tool main chamber residual atmosphere and walls. Instrumental setting and acquisition mode require particular care in their determination. Further, the H background signal detected by ToF-SIMS is strongly dependent on the matrix, i.e., the analyzed layer composition, thus it is particularly difficult to determine the ultimate H detection limit for the pGaN material. By working on acquisition protocols, we optimized the detection limit and correlated the concentration value obtained with GaN and electronic properties. In particular, Hall measurements show that sheet resistance values are not strictly correlated with H content.

[1] Nardo et al (2022) J. Phys. D: Appl. Phys. 55 185104

[2] S. J. Pearton, A. Y. Polyakov (2010) Chem. Vap. Deposition, 16: 266-274

[3] Y. Nakagawa et al. (2004), Japanese Journal of Applied Physics, 43(1R) 23

Most funding organisations in Europe, USA, and increasingly worldwide, require that data from projects they support be published in an open manner. The acknowledged best practice for this is to follow the ‘FAIR Guiding Principles for scientific data management and stewardship’ [1]. These principles lay out recommendations for both the way data should be presented, and also the metadata relating to the experiments or studies that produced those data. The FAIR Principles define four interlinked categories, by which data should be Findable, Accessible, Interoperable and Reusable.

Related to this, Sir Tim Berners-Lee, the inventor of the Worldwide Web, has defined a 5-star Open Data Plan for data sharing [2]. These stars represent the degree to which data can be accessed and reused by others, with the top rating of five stars being linked open data that is available to all, and ‘machine actionable’. Machine actionability means that our data is presented in such a way that a computer can interpret its meaning and optionally direct a suitable workflow.

In the SIMS community we may share our data, but it is not easily accessible or reusable by those outside our immediate circle. This not only prevents our data being reused by others in their own research, but also inhibits the development of third-party data analysis packages which could grow the technique in unforeseen directions.

Here we present FAIRSpectra, a community-directed project to improve the data sharing practice in the field of SIMS. This activity will:

• Develop a common vocabulary so we can communicate with clearer understanding.
• Deliver this common vocabulary in a standards compliant format.
• Develop a file structure in an open standard file format.
• Produce tools to read and write these data and metadata formats in a range of computer languages.
• Generate training materials to enable the best use of these outcomes.

Benefits of FAIRSpectra will include:

• Ease of integration of our data with existing statistical and machine learning software.
• Better storage and accessibility of our data, in both private and public data stores.
• Greater compliance with funder expectations, potentially leading to more funding.

We invite all interested users to visit FAIRSpectra at https://fairspectra.net to engage in this process and help shape the future of data sharing in SIMS.

[1] Sci Data 3, 160018 (2016). https://doi.org/10.1038/sdata.2016.18

[2] https://5stardata.info/

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is one of the most important techniques for chemical imaging of nanomaterials and biological samples with high lateral resolution. However, low ionization efficiency limits detection of many molecules at low concentrations or in very small volumes.

Matrix-Enhanced SIMS (ME-SIMS), in which an organic matrix is added to the sample, is one promising approach to enhancing ion yield for biomolecules. Optimizing this approach has, however, been challenging because the processes involved in increasing the ion yield in ME-SIMS are not yet fully understood.

To better understand the roles of proton donation and reduced fragmentation on lipid molecule ion yield, ME-SIMS has been combined with cluster primary ion analysis. A DPPC/matrix model system as well as mouse brain cryo-sections which were vapor coated with matrix have been studied. The influence of primary ion species and cluster size have been investigated. Additionally, matrices that vary in acidity have been studied.

The studies reveal that multiple mechanisms are important for enhancing the yield of large molecular ions. Strong evidence that reduced fragmentation of the analyte is a major mode of action of ME-SIMS was observed in both the model system as well as the mouse brain tissue samples. Proton donation from the matrix to the analyte was found to be significant and increased with more acidic matrixes. In addition to these mechanisms, incorporation of the analyte in the matrix and surface segregation of the analyte were shown to play important roles.

These investigations contribute an important advance in the understanding of the mechanisms involved in molecular ion yield enhancement in ME-SIMS. This work demonstrates that cinnamic acid derivative matrices can provide a dramatically softer desorption environment for lipid analysis. In fact, with matrix, Bi₁⁺ primary ions generated nearly an order-of-magnitude greater molecular ion to fragment ion ratio than could be obtained using large Ar gas cluster primary ions without the matrix. This demonstrates a strong potential for improved molecular analysis along with the advantages of the nanoscale focus of the Bi LMIG.

One of the most important thin-film solar cell materials is Cu(In,Ga)Se₂ (CIGS). It reaches a maximum conversion efficiency of 23.6%[1]. Flexible and lightweight solar modules are possible[2]. Traditionally, in a standard stack the CdS buffer forms the pn-junction together with the CIGS absorber. However, due to optical losses in the short wavelength region and in order to improve the ecological foot print of the CIGS solar cell, there are efforts to replace CdS with the more transparent material Zn(S,O)[3].

The band alignment between Zn(S,O) and CIGS depends on the [Ga]/([Ga]+[In]) (GGI) ratio in the absorber material as well as on the sulfur content of the buffer layer. It strongly affects the transport of charge carriers generated by the absorption of light, which in turn is a limiting factor in power conversion. Thus, the [S]/([S]+[O]) ratio (SSO) in the Zn(S,O) buffer plays an important role for optimizing the solar cell performance. Usually, for quantification of the sulfur concentration in Zn(S,O), layers are deposited on a glass substrate and the SSO ratio is estimated from their bang gap as determined by optical transmission measurements. However, the identified SSO ratio in bare layers mostly deviates from the expected theoretical value in the stack, which corresponds to the realized solar cell performance. This raises the question, if the SSO ratio in Zn(S,O) is changed during device processing.

Here we investigate the layer stack ZnO:Al/(Zn,Mg)O/Zn(S,O)/CIGS with ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectroscopy), encompassing the front contact, buffer layers, and absorber layer of the solar cell. The determination of SSO in a complete ZnO:Al/(Zn,Mg)O/Zn(S,O)/CIGS layer stack is a challenge, since the first three layers all contain the elements Zn and O. How can we distinguish between the oxygen in Zn(S,O) from that in (Zn,Mg)O (ZMO)? In our work, we show a way to separate the information from ToF-SIMS data and to quantify it. The SSO differences between Zn(S,O) deposited by sputtering and by chemical deposition can clearly be seen.

[1] https://www.nrel.gov/pv/interactive-cell-efficiency.html

[2] T. Feurer et. al.; Progress in thin film CIGS photovoltaics – Research and development, manufacturing, and applications Progress in Photovoltaics Volume 25, Issue 7, July 2017, p. 645-667; DOI: 10.1002/pip.2811

[3] Xiaowei Jin et. al.; Chemical phases in the solution-grown Zn(O,S) buffer of post-annealed Cu(In,Ga)Se2 solar cells investigated by transmission electron microscopy and electroreflectance; Journal of Applied Physics 133, 165303 (2023) DOI 10.1063/5.0139264

An OrbiSIMS (Hybrid SIMS, IONTOF, Germany) is a dual analyser instrument combining a Time-of-Flight (ToF) mass spectrometer (MS) and an Orbitrap^TM MS, which confer advantages of speed and high-performance mass spectrometry, respectively [1]. There are now several instruments in operation around the world and metrology is needed to help ensure repeatability and reproducibility of the intensity scale. In 2021, we conducted a systematic study of two key parameters in the transfer optics on the transmitted secondary ion intensities [2]. Recently, we have conducted a systematic study of the noise characteristics of the Orbitrap using OrbiSIMS instruments at NPL and at IONTOF [3]. The VAMAS TWA 2 A37 MS interlaboratory comparison aims to build on the methods previously published and study reproducibility of OrbiSIMS experiments for organic and inorganic materials.

Measurement of the Orbitrap^TM noise distribution requires a source of ions that is stable over the time frame of the measurements. The protocol includes simple measurement of a reference silver sample across a range of ion intensities, beam currents and how to measure stability of the primary ion beam current at the sample (typically <1% RSD over a 10-minutes period). The protocol also allows the linearity of the intensity scale to be established.

The Orbitrap^TM requires the ions to have a potential of approximately 50 V and lower kinetic energy distribution than results from the SIMS collision process. Consequently, the sample is biased by a sample target voltage, V_T, necessary to match the acceptance window of the Orbitrap and a bespoke transfer system using an ion guide with helium gas at a pressure, P, which slows the ions and reduces their kinetic energy distribution through elastic collisions with gas atoms. The data acquired using the protocol will be used to map secondary ion intensity in function of V_T and P, as we reported previously. [2].

The protocol will be discussed and participation in the study is encouraged. Samples and protocol will be sent to participants by the end of 2023 and data should be reported by April 2024.

[1] M. K. Passarelli et al., “The 3D OrbiSIMS—label-free metabolic imaging with subcellular lateral resolution and high mass-resolving power,” Nat. Methods, no. november, p. nmeth.4504, 2017, doi: 10.1038/nmeth.4504.

[2] L. Matjacic et al., “OrbiSIMS metrology part I: Optimisation of the target potential and collision cell pressure,” Surf. Interface Anal., no. November 2021, pp. 1–10, 2021, doi: 10.1002/sia.7058.

[3] M. R. Keenan et al., “In preparation.”

Cellulose is the most abundant organic polymer found in nature and it has been historically exploited for many technological applications. Microcrystalline cellulose (MCM) is a purified, partially depolymerized by-product of fibrous plant cellulose that has already regulated and authorized applications as food additive. Nano-sized cellulose fibres can then be extracted from their micro-counterparts. Nanocellulose (NC) is an emerging advanced nanomaterial with several potential applications in the fields of medicine, energy, food and consumer products. NC can be classified in three types according to its source material: (1) nanofibrillated cellulose (NFC), (2) nanocrystalline cellulose (NCC), and (3) bacterial NC (BNC). Several technological pathways exists for the production of NC, exploiting the different biological sources, which in turn affect many physicochemical properties and ultimately the NC surface chemistry. Understanding the variability in the characteristics of different NC materials is crucial for reliable development of NC-based products and their safety assessment.
Increased attention towards NC use in food applications requires a thorough risk assessment that lays its foundation on a careful evaluation of NC material physicochemical properties. Investigating physicochemical properties of NC materials under the conditions applied for in-vitro testing is a prerequisite for proper hazard assessment and for understanding the underlying biochemical mechanisms occurring during NC interactions with living cells and tissues. Therefore we realized a detailed dataset of the physicochemical properties for each different type of NC material, including a microcrystalline cellulose material reference, using a set of orthogonal nano-analytical techniques. The objective was the realization of an interpretative framework for the subsequent toxicity experiments. The study involved Time-of-Flight Secondary Ions Mass Spectroscopy (ToF-SIMS) for the analysis of macromolecular chemistry, x-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) for the characterization of the functional groups chemistry, X-ray diffraction analyses (XRD) for characterization of the crystalline structure and transmission electron microscopy (TEM) for morphological characterization.
The NC materials were ranked in order of decreasing crystallinity, as measured by XRD, where BNC exhibited the highest and NFC “TEMPO-oxidized” the lowest crystallinity value. Functional groups chemistry analysis via XPS and FTIR showed the appearance of COO- functionalities in the NFC Tempo (i.e. catalytic oxidation) samples that are absent in other formulations. The appearance of these residual groups can be attributed to the interaction of NC hydroxyl functionalities and the catalyst oxygen radical. The resulting disruption of the hydrogen bonds network between the NC chains can be further correlated to the loss of crystalline organization observed via XRD. Chemical structure analysis using ToF-SIMS data, processed via multivariate approach (principal component analysis, PCA,) is able to separate the samples based on a first component describing the glucose monosaccharide structure and a second component describing oxidized groups. Samples grouping obtained via PCA reflects individual properties differences measured independently with orthogonal techniques.
NANOCELLUP project has received funding from the European Union through an EFSA grant (GA GP/EFSA/SCER/2020/04). This communication reflects only the author’s view and EFSA is not responsible for any use that may be made of the information it contains.

Introduction

Silicon carbide (SiC) and diamond are wide bandgap semiconductors that have begun to emerge with the development of high-power electronic devices. They have outstanding physical and chemical properties, and are therefore promising materials in several fields of applications: light emitters, high temperature and high-power electronics, high-power microwave devices, micro-electromechanical system (MEMS) technology, substrates...

Offering extreme sensitivity, high depth and lateral resolution together with high throughput, dynamic SIMS (Secondary Ion Mass Spectrometry) proves extremely useful for studying SiC and diamond materials.

Instrumentation

The CAMECA IMS 7f-Auto is a magnetic sector mass analyzer dedicated to dynamic SIMS measurements. It offers depth profiling with excellent detection limits (ppb to ppm) for both dopants and contaminants (H, C, N, O). It also provides unique sub-μm resolution 2D and 3D imaging capabilities, as well as high throughput and automation.

Different applications covered by the CAMECA IMS 7f-Auto related to the development of SiC and diamond materials will be presented.

SiC

Despite the rapid evolution of the SiC technology in recent years, the SiC growth process still faces significant challenges that limit device performance. Optimized doping and reduced impurity incorporation are essential for improving the performance and reliability of SiC devices.

Analytical conditions and data obtained in SiC samples using the CAMECA IMS 7f-Auto will be presented.

Diamond

Many studies focus on the nature and the impact of impurities in diamond thin films synthetized by chemical vapor deposition (CVD). Nitrogen (¹⁴N) is a well-known impurity in synthetic diamonds; it influences growth phenomena, and it is a compensator for acceptor states. It needs to be accurately controlled and measured using dynamic SIMS.

Data obtained on the IMS 7f-Auto on diamond-based structures will be presented.

Conclusions

As for Si technology development for integrated circuits, dynamic SIMS technique is a key tool for R&D of novel materials, as it provides the in-depth distribution of trace elements (dopants and contaminants) with excellent detection limits and high throughput. In addition to depth resolution, dynamic SIMS also offers high lateral resolution that can be used to investigate the non-uniformity of trace elements.

Whilst the success of mRNA-based vaccine in protecting against SARS-CoV-2 infection, there is still much to learn about the role of lipid nanoparticles (LNP) in initiating an immune response. This project aspires to gain some insight into the metabolic impact of LNP’s using state of the art characterisation techniques such as mass spectrometry imaging.

Lipid nanoparticles are delivery vehicles that have unique components that are not endogenously present in cells. These components will be used to follow the delivery vehicle and provide a chemical “fingerprint” for the nanoparticle when using characterization techniques such as secondary ion mass spectrometry (SIMS), specifically 3D-OrbiSIMS. Conventional metabolomic techniques including liquid chromatography mass spectrometry (LC-MS) generally required extensive sample preparation and does not provide any 3D imaging or distribution information for specific chemical compounds.

This work will build on previous work to improve our capacity to interrogate the physiological environments by mapping the chemical fingerprint of the delivery vehicle and metabolic impact of exogenous vaccine mechanisms over time with LNP’s delivered to in-situ cell models and utilising 3D-OrbiSIMS to analyse the metabolomic impact of the LNP’s on the cells over time with hopes to provide key mechanistic evidence to improve the design of vaccine and delivery vehicles by providing insight regarding how delivery occurs and influences the cellular environment ^[1].

[1] Suvannapruk, W. et al. Single-Cell Metabolic Profiling of Macrophages Using 3D OrbiSIMS: Correlations with Phenotype. Anal Chem (2022)

CMOS image sensors, which are mostly used in consumer electronic devices, represent a low cost alternative for the acquisition of high-resolution X-ray and neutron radiographic images with application in biology, electronic component inspection and paleontology. Nevertheless, in order to model the response of the sensor, it is required to know its architecture defined by the composition, size and distribution of the different regions. In that regard, TOF-SIMS has been widely used for characterizing semiconductor devices although the selection of optimal analysis conditions is not trivial at all.

In this work, we present the characterization by TOF-SIMS of a commercial off-the-shelf CMOS image sensor intended to be used as an X-ray detector for acquiring radiographic images of wood specimens. The analyzed sensor is covered with an array of organic microlenses which poses a challenge for the TOF-SIMS analysis. Different analysis conditions (i.e. primary ion species, sputter species and gas flooding) were used for optimizing the detection of the secondary ions of interest, while different strategies (i.e. imaging of cross-sections, depth-profiling from top-surface, and removal of organic lenses) were used for dealing with topographic effects. The performed analysis allow us to detect the presence of a borophosphosilicate glass (BPSG) layer which was crucial for improving the modeling of the CMOS image sensor response and explaining the experimental X-ray image data acquired with the sensor.

This contribution reviews our recent investigations involving (bio)molecule desorption and transfer using large argon cluster ions. Experimentally, the interaction of keV Ar cluster ion beams (Ar⁺_1000-5000) with a reservoir of organic molecules was used to transfer (i) peptides and lysozymes onto a collector, with retention of their bioactivity, paving the way to a new solvent-free method for complex biosurface nanofabrication [1,2]; (ii) MALDI matrix molecules on tissues of interest (brain and endometrium cross-sections) in situ the ToF-SIMS instrument for their analysis and imaging with improved sensitivity [3] and (iii) biomolecules from tissues to a series of substrates (including low MW matrix layers), also for an analytical purpose [4]. In parallel, molecular dynamics (MD) simulations provided access to the detailed microscopic view of the interactions, out of reach of the experiments and needed for their understanding. For instance, our reactive force field (ReaxFF) simulations explained the influence of the cluster parameters and surface structure on lysozyme desorption, fragmentation and denaturation [5].

[1] V. Delmez, H. Degand, C. Poleunis, K. Moshkunov, M. Chundak, C. Dupont-Gillain, A. Delcorte, Deposition of Intact and Active Proteins In Vacuo Using Large Argon Cluster Ion Beams, J Phys Chem Lett. 12 (2021) 952–957.

[2] V. Delmez, B. Tomasetti, T. Daphnis, C. Poleunis, C. Lauzin, C. Dupont-Gillain, A. Delcorte, Gas Cluster Ion Beams as a Versatile Soft-Landing Tool for the Controlled Construction of Thin (Bio) Films, ACS Appl Bio Mater. 5 (2022) 3180–3192.

[3] T. Daphnis, B. Tomasetti, V. Delmez, K. Vanvarenberg, V. Préat, C. Thieffry, P. Henriet, C. Dupont-Gillain, A. Delcorte, Improvement of lipid detection in mouse brain and human uterine tissue sections using in situ matrix enhanced secondary ion mass spectrometry, J. Am. Chem. Soc. Mass Spectrom., Submitted.

[4] B. Tomasetti, C. Lauzin, A. Delcorte, Microvolume expansion with large argon clusters: An effective approach to enhance the ion signal in ToF-SIMS, Anal. Chem., Submitted.

[5] S. Bertolini, A. Delcorte, Reactive molecular dynamics simulations of lysozyme desorption under Ar cluster impact, Appl. Surf. Sci. 631 (2023) 157487.

In this work, we demonstrate the feasibility of determining 3D structures of native biomolecular complexes with high resolution and accuracy by integrating 3D-OrbiSIMS with molecular modelling and simulations approaches.

3D-OrbiSIMS combines the GCIB based fragmentation in a SIMS setup with the high speed and resolution of Orbitrap analyzers to facilitate an unprecedented level of mass spectral molecular analysis for a range of materials (hard and soft matter, biological cells and tissues) at pico molar sensitivity. First developed in 2017 for label-free metabolic imaging, it has been successfully applied to a range of fields, including neuroscience, cancer biology, and materials science to study protein localization, lipid composition, and metabolite distribution in situ. However, its application to biolomolecular structure characterisation is yet to be investigated.

We started by optimising our sample preparation and data collection conditions under varying buffer and temperature conditions to ensure that the bimolecular complexes retain their native-like, hydrated, structural integrity. Our results indicate that the 3D-OrbiSIMS spectrum contains more chemical information under cryogenic conditions and the mass spectrum range is sufficient to probe neutral losses of RNA fragments up to 6 nucleotides in length. We further ascertained that this mass range is sufficient to characterise more than 80% of the biologically relevant RNA/P complexes deposited in the PDB. Next, we show that even though the ballistic fragmentation of the samples by the Argon beam is stochastic in nature, the Cryo-OrbiSIMS experiments can reproducibly generate unique mass fingerprints for all bimolecular complexes studied under different physiological conditions and / or biological conditions. Further, peak assignments of the mass spectrum revealed that the mass data also encoded information about the native structures and plasticity of the complexes studied. Finally, by generating novel pipelines for incorporating Cryo-OrbiSIMS data as restraints in molecular modelling algorithms and molecular dynamics simulations, we were able to construct native-like 2D-folds and atomic resolution 3D-structures of the RNA systems studied.

In conclusion, By benchmarking 3D-OrbiSIMS against existing methodologies, we have provided a critical validation of the technique. This positions 3D-OrbiSIMS as a transformative tool for uncovering the intricate details of native biomolecular complexes. Further, we have also successfully pushed the boundaries of technique’s capabilities in order to propel a step-change in structural characterization by native Mass Spectrometry techniques.

Reactive molecular dynamics (MD) simulations were conducted to investigate the desorption and soft landing of proteins transferred into the vacuum using large argon clusters. Experimentally, the interaction of argon cluster ion beams (Ar⁺_1000-5000) with a target biofilm was previously used in such a manner to transfer peptides and lysozymes (with retention of their bioactivity) onto a collector, paving the way to a new solvent-free method for complex biosurface nanofabrication. However, the experiments did not give access to microscopic view of the interactions needed for their full understanding, which can be provided by the MD model.

Our reactive force field (ReaxFF) simulations explain the influence of the cluster parameters (size and kinetic energy) and surface structure (thickness of the protein layer) on the fragmentation and denaturation of the desorbing proteins. In addition, ReaxFF simulations were performed to clarify the soft landing of the lysozymes and their fragments on collectors of different natures (gold and graphite). The results show that fragmentation occurs preferentially during soft landing on the rigid gold surface, but it is also affected by the impact angle of the molecules. Additionally, the presence of defects in the graphite layer can induce reactions between the (fragments of) proteins and the surface.

Secondary Ion Mass Spectrometry (SIMS) is a robust technique for 3D imaging of inorganic, organic, and biological systems, which offers unparalleled sensitivity and spatial resolution. Recently, the introduction of water cluster projectiles dramatically increased the ionization probability enabling for much more detailed molecular composition maps [1, 2].

Our knowledge of the mechanisms involved in the sputtering by water clusters (H₂O)_n is currently limited. The signal enhancement is present only for a very narrow range of kinetic energy per water molecule. Our recent simulations show that this phenomenon is highly correlated with the number of sample molecules ejected with a partial shell of water molecules [3].

Water can also possess a detrimental effect on the sputtering efficiency. In this work, we use the reactive molecular dynamics simulations of a trehalose surface covered with a few-nanometer thin film of water to investigate the effect of the overlayer thickness on the sputtering yield and mass spectrum. We also discuss how dissolving trehalose molecules in the film influences the ejection phenomena.

This work was supported by a Polish National Science Centre Grant 2019/33/B/ST4/01778. MD simulations were performed using the PLGrid infrastructure.

(1) Sheraz née Rabbani, S.; Barber, A.; Fletcher, J. S.; Lockyer, N. P.; Vickerman, J. C. Enhancing Secondary Ion Yields in Time of Flight-Secondary Ion Mass Spectrometry Using Water Cluster Primary Beams. Anal. Chem. 2013, 85 (12), 5654–5658. https://doi.org/10.1021/ac4013732.

(2) Sheraz, S.; Tian, H.; Vickerman, J. C.; Blenkinsopp, P.; Winograd, N.; Cumpson, P. Enhanced Ion Yields Using High Energy Water Cluster Beams for Secondary Ion Mass Spectrometry Analysis and Imaging. Anal. Chem. 2019, 91 (14), 9058–9068. https://doi.org/10.1021/acs.analchem.9b01390.

(3) Kański, M.; Hrabar, S.; van Duin, A. C. T.; Postawa, Z. Development of a Charge-Implicit ReaxFF for C/H/O Systems. J. Phys. Chem. Lett. 2022, 13 (2), 628–633. https://doi.org/10.1021/acs.jpclett.1c03867.

The first transistors were known as “planar” transistors because all elements of the transistor, (gate, source, drain) were situated on a 2D plane. For many following generations, the performances of the planar transistors could be increased by shrinking the gate length. As the transistor’s dimensions continued to decrease, the space between the source and drain decreased to the point where the gate was not able to avoid leakage current issues. Because of this, the industry has shifted from planar to “3D” transistors, known as FinFETs. Another evolution of the transistor is currently underway in the industry. These next-generation transistors are known as “Gate-All-Around” (GAA) transistors using stacked horizontal nanosheets. A more recent evolution of the GAA devices sees the n and p channels moving closer together or stacked vertically in both forksheet or 3D complementary FET (CFET). The evolution of the device architecture from 2D (planar) to 3D (CFET) has always of course been accompanied by an improvement of the patterning capabilities, which turned to be more and more challenging nowadays with the reduced dimensions and the increased complexity of the devices to produce. Together with the change of architecture, the industry has implemented and is still investigating the use of new materials, such as high-k materials replacing the gate SiO2, strained-Ge and SiGe thanks to their excellent hole and electron mobilities and even more recently 2D materials such as MoS₂ or WS₂ as new channel materials.

All these evolutions (change from 2D to 3D architecture, size reduction of the devices with dimensions smaller than the SIMS beam spot size, complexity of the mass spectra, with more and more mass interferences due to increased number of elements present in the devices, ...) have made the SIMS analysis more complex to perform in order to retrieve accurate information about bulk and layer composition, dopant quantification, layer uniformity, .... In this paper, we will review how SIMS has evolved during the past years to remain relevant to the microelectronic industry. We will show how the use of concepts such as Self Focusing SIMS (SF-SIMS) [1] and the introduction of new developments in the SIMS technique such as the Orbitrap^TM mass analyzer and the combination of SIMS with other complementary techniques such as AFM, allow to extend the application of SIMS in the semiconductor industry for the next decades. Several examples will be discussed.

References

[1] A. Franquet et al., Appl. Surf. Sci. 365 143 (2016).

Fuel injectors and filters are critical engines components which are affected by deposit formation, causing decreased fuel efficiency and increased harmful emissions. The industry has sought to understand deposit formation by employing a range of analytical techniques on these challenging samples. SIMS provided a new perspective on deposit analysis, initially with ToF-SIMS enabling extraction of spatial and depth information to reveal a chemically layered deposit structure, but only small fragment ions could be identified. More recently, the debut of OrbiSIMS brought a combination of spatial information with high-resolution mass spectrometry, yielding a molecular characterisation in three dimensions which indicates the origin of various deposit components. The application of OrbiSIMS to both diesel and gasoline deposits suggested chemistry of lubricant oil origin, inorganic salt contamination, and carbonaceous material found deep within the deposit. Complementary X-ray photoelectron spectroscopy (XPS) depth profiling provided validation with elemental quantification, notably confirming a high sodium salt concentration in a diesel injector sample. Further work by Edney et al. evidenced a progressive carbonisation of deposits over time, focusing on polyaromatic precursors which were corroborated by the softer ionisation technique of AP-MALDI Orbitrap^TM mass spectrometry. Our recent work applies OrbiSIMS with XPS to the analysis of “lab-grown” deposits formed using a laboratory benchtop test serving as a cheap and rapid simulation of injector deposit formation. We investigate the relationship between deposit composition and fuels and contaminants, finding a typically carbonaceous matrix that is influenced by components in the fuel such as biodiesel or sodium. With these new understandings, research can be focused on mitigation strategies for these deposit chemistries and structures to ensure optimal and sustainable use of internal combustion engines during the transition towards decarbonisation.

In recent years, it has been discovered that silanes can effectively safeguard metals from corrosion. By carefully choosing appropriate silane adhesion promoters, a monolayer of silanes firmly bound to the surface forms a protective film on for example aluminium, titanium, and other metals[i]. It was later found that sol-gel chemistry provides a better anti-corrosive strategy compared to separate silane molecules because it allows for the creation of a more robust and homogeneous coating on the surface of the material. The so-deposited sol gel is a uniform, dense, highly crosslinked, and continuous film that is tightly bound to the surface of the substrate, hence giving rise to long-lasting protection against environmental factors such as moisture, oxygen, and salt[ii].

Furthermore, sol-gel chemistry allows for the incorporation of various functional groups into the coating, allowing additional benefits such as improved adhesion, durability, and flexibility It also makes possible the occurrence of anchoring groups to which subsequent coating layers can adhere, making sol-gels an ideal replacement for chromium-based conversion coatings[iii],

This paper suggests an innovative characterization approach of silica-based conversion coatings on an Al substrate by, on the one hand, salt spray tests and, on the other hand, time-of-flight secondary ion mass spectrometry (ToF-SIMS) performed in depth profile mode by a gas cluster ion beam source (GCIB). For this study, we considered 3 Al substrates which were coated by films with a composition corresponding to various commercial formulations. Whereas the salt spray tests determine differences in anticorrosion properties between the 3 samples, ToF-SIMS provides molecular information throughout the entire coating and even down to the beginning of the Al substrate. Therefore, both the inner composition of the conversion coating and the interface bond of this one to the Al substrate could be studied. The ToF-SIMS measurements revealed Si₂O₂⁺ and SiOAl⁺ fragments which both contribute to understanding the differences in the anticorrosion performances. Si₂O₂⁺ relates to the crosslinking of the coating and subsequently takes part in the barrier properties. SiOAl⁺ originates from the interface bond and is a clue for the “conversion coating” of the deposited layer. Differences in depth profile of Si₂O₂⁺ and SiOAl⁺ between the 3 samples are interrelated to the respective anti-corrosion performance of these ones.

[i] De Graeve, I., Vereecken, J., Franquet, A., Van Schaftinghen, T., & Terryn, H. (2007). Silane coating of metal substrates: Complementary use of electrochemical, optical and thermal analysis for the evaluation of film properties. Progress in Organic Coatings, 59(3), 224-229.

[ii] Wang, D.; Bierwagen, G. P., Sol–gel coatings on metals for corrosion protection, Progress in Organic Coatings, Volume 64, Issue 4,2009, Pages 327-338.

[iii] WO2010/095146A1: Anti-corrosion sol-gel hybrid coating on zinc and zinc alloy steel sheets and preparing method thereof.

The increasingly complex architectures and diversity of materials used in modern semiconductor devices makes their characterization challenging. TOF-SIMS analysis is particularly well suited to dopant and multilayer analysis in such devices, but standard approaches such as surface imaging or dual-beam depth profiling can be limited when faced with deeply buried interfaces and very heterogeneous samples. This is the case for through-silicon vias and copper pillars. These objects are typically several tens of microns in dimension and are used in 3D integration approaches to connect chips together. To address this type of sample, the capabilities of a TOF-SIMS instrument can be extended by the use of an in situ focused ion beam (FIB) gun. This is often a gallium source FIB, but other sources can be used such as Xe plasma sources to obtain higher etch rates for larger samples. In fact, even in the absence of a dedicated FIB column, the LMIG source (Ga, Bi, Au etc) that is normally used for spectroscopy on the instrument can also be used without pulsing to produce a continuous high current beam for FIB milling. The drawback of this method is that the sample must be rotated between milling and imaging steps and the LMIG parameters will require changing. There may also be milling artefacts arising from the presence of a mix of monoatomic and cluster ions when a bismuth or gold source is used.

The use of a dedicated FIB column opens up the possibility of performing FIB-TOF-SIMS tomography experiments and limits sample drift and re-positioning errors as the sample may be kept in the same position. However, FIB-TOF-SIMS tomography experiments can be time-consuming (overnight analysis to several days) and the investigated volume is limited by the sputter rates obtainable. To overcome these limitations, a prescreening with a non-destructive X-ray imaging technique can help to identify positions of interest for FIB-TOF-SIMS tomography to be performed on. This can be TSVs containing filling defects (voids) that can then be investigated at high resolution and with compositional information by FIB-TOF-SIMS. Another important question is whether copper diffused out from the TSV, through the diffusion barrier (often a thin layer of metal nitride) to the surrounding silicon. The presence of copper is deleterious for electronic properties and once present in silicon can diffuse relatively fast to active areas of the device. The engineering of barrier layers is routinely performed by depth profiling on full wafer samples to maximize layer quality and presence of certain defects may vary between full sheet deposition vs conformal filling of high aspect ratio holes. The use of an in situ FIB allows both tomography experiments and depth profiles to be performed on the side of a FIB-cut parallel to the object of interest.

Part of this work, carried out on the Platform for Nanocharacterisation (PFNC), was supported by the “Recherches Technologiques de Base” of the French National Research Agency (ANR).

Recent advances in 3D electron microscopy have enabled spectacular progresses in our understanding of the ultrastructure of many organisms and tissues. However visualizing the metabolism within its structural context is key to understand and identify the biological mechanisms at stake¹. In this light, correlating laterally resolved molecular information from TOF-SIMS (up to 100-400 nm lateral resolution) with structural data from electron microscopy (5 nm lateral resolution) is a promising approach as evidenced with several examples.

During a symbiotic association between two organisms, both host and symbiont metabolism undergo deep modifications². As such, the correlation of SEM and TOF-SIMS data is a useful method to understand how the two partners are remodeled structurally and metabolically. Our first results suggest that the host exerts its control through preferential allocation of some nutrients to boost symbiont productivity.

Additionally, the microalga Coelastrella sp. PCV³ has recently been shown of high interest for uranium bioremediation. Our approach reveals the how uranium is being sequestrated inside specific compartments of the cell.

[1] J. Decelle, et al. Trends Cell Biol. Vol 3 (2019), 173-188.

[2] C. Uwizeye, et al. PNAS. Vol 118 (2021), e2025252118.

[3] C. Beaulier, et al, BioRxiv (2023) 2023-06. 29.546994.

2D transition metal dichalcogenides are attracting great interest thanks to their atomic layer thickness, extraordinary (opto)electronic, chemical and thermal properties. However, it has become increasingly more difficult to characterize, chemically and electrically, this kind of materials and their interfaces. Indeed, conventional methodologies, including scanning probe microscopies, fail to capture insight in the chemical and electronic nature of the semiconductor, albeit vital to understand its impact on the semiconductor performance. Therefore, in this work, we present a unique and universal in-situ approach [1] to characterize thin WS₂ layers by combining time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM) in conductive mode. In this way it was possible to map chemical differences between regions of different electrical conductivity in the 2D material, thanks to the accurate chemical information achievable with ToF-SIMS combined with the atomic resolution attainable with AFM. Surprisingly, WS₂ regions of lower electrical conductivity possess a larger amount of sulfur compared to regions with higher conductivity, for which oxygen was also detected. Such difference in chemical composition likely roots from the non-homogeneously terminated sapphire starting surface, altering the WS₂ nucleation behavior and associated defect formation between neighboring sapphire terraces [2]. These resulting sapphire terrace-dependent doping effects in the WS₂ hamper its electrical conductivity. Thus, we demonstrated how accurate chemical assignment at sub-micrometer lateral resolution of atomically thin 2D semiconductors is vital to achieve a more detailed understanding on how the growth behavior affects the electrical properties.

[1] V. Spampinato et al. Anal. Chem. 92 (2020) 11413

[2] Y. Shi et al. ACS Nano 15(6) (2021) 9482

Traditionally, Focused Ion Beam (FIB) platforms are coupled with an electron beam column (FIB-SEM) to perform in-situ sample preparation (FIB milling) and electron microscopy (EM), respectively. EM images can be acquired with the FIB column (secondary electrons, SE) or with the SEM column in different modes (SE, BSE, EBSD, STEM) with the possibility to perform chemical analysis (WDS/EDX). However, the electron beam probes for EDX analyses present very large interaction volumes within the sample (several µm) and EDX does not allow the detection of light elements (H, Li, ..) and trace elements (<1% in at.).

In the recent years, the ion sources integrated in FIB platforms have considerably improved in terms of source brightness, leading to better spatial resolution and current density, and versatility of available ion species. For example, the low temperature ion source (LoTIS) working with Cs ions and reaching a brightness of 10⁷ A cm^-2 sr^-1, which is much higher than the surface ionisation Cs source (10² A cm^-2 sr^-1) available on conventional SIMS instrument [1-2], can produce nm-sized probe sizes while maintaining high ion currents. These new sources are of great interest not only for their ability to mill a variety of structures, but also to provide structural and morphologic information with (sub)-nm resolution in SE.

In this global context, we developed compact magnetic sector SIMS systems specifically designed and adapted for the ZEISS ORION NanoFab Helium Ion Microscope (HIM) [2-3], the Thermo Fisher DualBeam [4] and the ZeroK FIB:ZERO platform. These instruments are capable of producing elemental SIMS maps with sub-15 nm lateral resolution, while maintaining the performance of the FIB platform in terms of secondary electron (SE) imaging and nanomachining. The latest compact SIMS generation is equipped with a novel continuous focal plane detector (FPD). This system allows for the detection of all masses in parallel for each single pixel, resulting in acquisition times as low as 1 s to obtain a full mass spectrum or 2 min to obtain a 512 x 512 pixel SIMS image with highest signal-to-noise ratio and excellent dynamic range. [2]

This SIMS system is now operating on several multi-modal FIB platforms . Here, we will review the performance of the different FIB-SIMS instruments with a focus on new developments, showcase methodologies for high-resolution 2D and 3D chemical imaging, and give an outlook on new trends and prospects.

[1] B. Knuffman, A. V. Steele, and J. J. McClelland, J. Appl. Phys. 114, p. 044303 (2013)

[2] J. N. Audinot, P. Philipp, O. De Castro, A. Biesemeier, Q. H. Hoang, T Wirtz, Reports Prog. Phys. 84, p.105901 (2021).

[3] Dowsett and T. Wirtz, Anal. Chem. 89, 17, 8957–8965 (2017)

[4] O. De Castro, J.-N. Audinot, H. Q. Hoang, C. Coulbary, O. Bouton, R. Barrahma, A. Ost, C. Stoffels, C. Jiao, M. Dutka, M. Geryk, T, Wirtz, Analytical Chemistry, 94(30), 10754-10763 (2022).

Resonant Laser-ionization Secondary Neutral Mass Spectrometry (rL-SNMS) combines the spatial resolution of traditional static time of flight secondary ion mass spectrometry with the elemental selectivity of resonant laser ionization. A set of TiSa lasers is used to ionize only one selected element from the sputtered neutral cloud via a resonant multistep excitation scheme. For ultra-trace analysis of isotopes like ²³⁸Pu, non-resonant ionization of isobaric interferences, like ²³⁸U, are challenging to remove. Reference material is needed for an investigation of the different ionization efficiencies of relevant elements. The MetroPOEM project ^[1], aims to develop SI-traceable reference material to overcome this challenge. For rL-SNMS, such solid multi-element standards have specific requirements: homogeneity on the sub-micrometer scale with known isotopic composition. In this work we present a method for the production of homogenous U-Pu samples by fast Fe coprecipitation. The homogeneity of the samples was confirmed by ToF-SIMS and EDX. The elemental composition of the material was determined with ICP-MS measurements. The samples were used to determine the suppression ratios of non-resonant U in Pu rL-SNMS measurement. The presented method will be modified to produce homogenous sample material for other elements, and used to investigate relative ionization efficiencies for different elements.

^[1] MetroPOEM is a collaboration of 22 partners from 13 countries throughout Europe funded by EURAMET under grant number 21GRD09 https://www.npl.co.uk/euramet/metropoem

.

Aim: Cellular protein turnover has often been studied with mass spectrometry bulk analysis, however this method does not account for spatial differences of the turnover at single cell and subcellular level (e.g., organelle specificity). In this study, correlative transmission electron microscopy (TEM) and nanoscale secondary ion mass spectrometry (NanoSIMS) imaging were employed to investigate subcellular protein turnover in neuronal progenitor cells (NPCs). This integrative tool is a useful approach for many other investigations of biological mechanisms such as protein metabolism and cellular differentiation.
Methods: NPCs were incubated with different isotopically labeled (¹⁵N) amino acids for 48 h followed by an incubation with regular cell medium for pre-determined periods (chase time), from 0 h to 96 h. The cells collected after each chase time were then chemically fixed, embedded in resin and cut into thin sections. First, cells were imaged using TEM and the locations of various organelles within the cells were determined. Subsequently, the same cells were imaged with NanoSIMS providing information about the isotopic enrichment at the organelle level. By superimposing TEM and NanoSIMS images of the same cells, the ¹⁵N enrichment of individual organelles at the different chase times could be obtained.
Results and discussion: A heterogenous pattern of protein turnover across different cellular organelles was obtained, which could be related to previous data from Yousefi et al. about a protein’s localization influencing its turnover (Yousefi et al. 2021). This highlights a possible relationship between protein turnover and subcellular function. Additionally, significant differences in the subcellular distribution of ¹⁵N-enrichment from different ¹⁵N-amino acids were observed. These findings highlight the roles of different protein precursors in cellular protein turnover, as they might undergo distinctive metabolic pathways and thus are incorporated into specific proteins at specific cellular regions.

References: Yousefi, R.; Jevdokimenko,K.; Kluever, V.; Pacheu-Grau, D.;Fornasiero, E.F. 2021 Influence of Subcellular Localization and Functional State on Protein Turnover. Cells, 10, 1747

The presented study focused on two polymers poly(tert-butyl methacrylate) (PtBMA, Tg=117 °C) and poly(n-butyl methacrylate) (PnBMA, Tg=20 °C) and their interactions with biological materials.

In the first step, the impact of PtBMA stereoregularity on its interactions with peptides, proteins, and bacteria strains was studied for three stereoregular forms: isotactic (iso), atactic (at), and syndiotactic (syn). Principal component analysis (PCA) of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) data recorded for thin polymer films indicated a different orientation of ester groups, which in the case of iso-PtBMA are exposed away from the surface whereas for at-PtBMA and syn-PtBMA these are located deeper within the film. This arrangement of chemical groups modified the interactions of iso-PtBMA with biomolecules when compared to at-PtBMA and syn-PtBMA. For peptides, the affected interactions were explained by preferential hydrogen bonding and electrostatic interaction between the exposed polar ester groups of iso-PtBMA and positively charged peptides. In turn, for protein adsorption no impact on the amount of adsorbed proteins was observed. However, the polymer stereoregularity influenced the orientation of immunoglobulin G (IgG) and induced conformational changes in bovine serum albumin (BSA) structure. Moreover, the impact of polymer stereoregularity occurred equally for their interactions with Gram-positive bacteria (S. aureus), which absorbed preferentially onto iso-PtBMA films as compared to two other stereoregularities.

In the next step, the effect of temperature on the protein adsorption onto the PnBMA grafted brush coatings was studied. Due to glass temperature around 20 °C PnBMA is extremely interesting material for biomedical applications since its properties can be modified within the range of physiological temperatures. The combination of proteins molecules structure analysis with PCA of ToF-SIMS data revealed a temperature-dependent orientation of BSA as well as IgG molecules. BSA adsorbed to PnBMA coatings below Tg adopts such an orientation that Albumin 1 and Albumin 2 are exposed out of the surface, whereas for temperatures above transition, Albumin 3 is exposed. Similarly to BSA, the PCA of the ToF-SIMS data obtained for IgG immobilized at different temperatures onto PnBMA coatings clearly separates the IgG adsorbed onto the surface PnBMA below and above Tg. The analysis revealed a dominant head-on orientation for IgG adsorbed above Tg compared to a dominant end-on orientation for molecules adsorbed below the temperature of transition, which has a strong impact on their biological activity.

Biological molecules have been shown to exhibit specific cellular localizations, which relate closely to their functions. To understand the molecular mechanism of a cellular process, it is essential to obtain the spatial information of biomolecules and organelles in the cells, and their turnover dynamics and activity. Secondary ion mass spectrometry, with high a sensitivity, versatility, and spatial resolution, has been increasingly applied in biological research and neuroscience allowing the visualization of molecular localizations and turnover at the single cell and subcellular resolution. However, applications of SIMS alone is difficult for the biological interpretation due to its limitation in identifying specific cellular structures and organelles. Besides, information of large molecules, such as proteins, is completely lost due to the intense fragmentation, especially in NanoSIMS. Here, we resolved these problems using a correlative imaging approach using NanoSIMS and super resolution stimulate emission depletion microscopy (STED) to characterize the protein turnover dynamics of human neural progenitor cells (NPCs) at the organelle level. Alternatively, we developed dual labelling probes capable of binding to specific cellular proteins which can be visualized by both fluorescence microscopy and NanoSIMS imaging.

Correlating STED and NanoSIMS, we identified individual stress granules (SGs) in NPCs by STED microscopy and determined their protein turnover by NanoSIMS under the conditions of cellular ER stress (using ER stressor Thapsigargin) and stress recovery. SGs are membraneless organelles formed during cell stress as a cellular defensive mechanism to protect important cellular translational and signalling materials. However, the molecular mechanism of SG assembly and disassembly, and how they affect the cell recovery is not fully known. We found that SGs assemble by recruiting the proteins from the cytoplasm that exist before stress. In addition, the ER stress causes significant protein turnover impairment which could remain longer than commonly expected stress recovery period.

We have developed labelling probes, each containing a fluorophore and an element that is easily ionized by SIMS, particularly fluorine, boron, or iodine. These probes were demonstrated to label specific cellular proteins via click chemistry or immunostaining, and to visualize their localizations by fluorescence microscopy and NanoSIMS. We also generated a probe containing gold nanoparticles conjugated to nanobodies for specific protein imaging with NanoSIMS at subcellular resolution.

The correlative imaging approach and all the developed labelling probes offer a possibility of specific molecular imaging in SIMS extending to high mass biomolecules above metabolites and lipids.

Standard SIMS measurements of 2D materials may provide vital but ambiguous results - while the excellent sensitivity of the technique may enable the detection of various contaminants, the depth resolution may not be sufficient to localize them. However, in this case, it is not enough to just improve the resolution. Given that many 2D materials are or consist of atomically thin layers it is essential to reach the ultimate, i.e. atomic depth resolution. As a consequence, factors that limit the resolution like the mixing effect could not be only minimized but completely eliminated. At the same time, the established procedures should maintain sufficient secondary ion yield to ensure a reasonable signal-to-noise ratio. To achieve such accuracy it is essential to establish dedicated measurement procedures which are tailored for specific samples. Even though such procedures are time-consuming to set up and execute, the quality of the results justifies all difficulties:

• It is possible to not only detect but also precise localize various contaminants in graphene;
• SIMS instrument can be used to both, implant molybdenum sulfide with oxygen and then observe the temperature-induced stabilization of the MoS₂/MoO₃ heterostructure;
• Depth profiling of MXenes has revealed that these advanced materials are actually transition metal oxycarbides and not carbides as commonly assumed.

Since their invention in 1987 by Tang and Van Slyke, understanding the degradation mechanisms after environmental and/or electrical aging is essential to improve the performances of organic light emitting diodes (OLEDs). However, the study of thin aged organic multilayers (~100 nm thick) requires characterization techniques capable to probe small chemical changes with a high depth-resolution. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) are suitable surface-sensitive techniques providing complementary information: access to molecular information and the elemental chemical environment respectively. Nowadays, ToF-SIMS and XPS depth profiling are routinely used to investigate aged devices. However, the analysis and sputter beams used in these techniques may induce degradations on organic layers [1] and cause bond scission [2] that accumulate in burried layers. We developed a correlative depth-resolved protocol that aims to minimise damage related to analysis beams by analysing the surface of a bevel crater. This shallow angle bevel crater is formed using a continuous, linear variation of ion fluence across a rastered area of 800 × 800 µm². Typically, argon clusters of around 7500 atoms are used at an accelerating voltage of 5 kV. A comparison between an electrically-aged and fresh OLEDs (structure for green light emission) has been performed using this protocol. Electrical ageing consisted of maintaining a stable courant of 4 mA for 430h in order to produce sufficient degradation that would be visible by TOF-SIMS and XPS techniques. The greater degree of fragmentation of the characteristic molecular ions originating from the emissive layers as well as the electron transport and hole blocking layers is observed in ToF-SIMS spectra. XPS measurements confirm that the chemical environment of the elements present in those layers appears to change after ageing, in particular in the hole blocking layer.

1. Morgan, D.J., XPS insights: Sample degradation in X-ray photoelectron spectroscopy. Surface and Interface Analysis, 2023: p. 1-5.

2. Postawa, Z., Sputtering simulations of organic overlayers on metal substrates by monoatomic and clusters projectiles. Applied Surface Science, 2004. 231-232: p. 22-28.

Contamination detection and control play a critical role in achieving the semiconductor industry’s roadmap of zero failures. Compared to metal and particle contamination, knowledge of organic contamination and its detrimental effects is still limited. As devices are continuously scaled down, organic contamination is increasingly becoming a major yield-affecting factor. Previous studies of organic contamination on silicon oxide surfaces have focused on total carbon contamination and its effects on gate-oxide integrity. During wafer fabrication process, there are many possibilities for organic contamination to occur. Wet cleaning-induced organic contamination is one of them.

In recent years the focus of contamination reduction has changed from frontend of line to the backend (assembly). Here especially the packaging of a semiconductor device including the wire bonding process has become more important. During the assembly of a finished device the process where the wire is attached to the bond pad is critical as a good contact of the wire (connection to the outside world) is crucial for reliable functioning of the finished product.

This presentation will focus on examples of organic contamination in the backend process. The first example will show how low IMC coverage (inter metallic compound) formation (<60%) was observed during wire bonding. The hypothesis that the low IMC is caused by bond pad surface contamination is discussed. It will be demonstrated that ToF-SIMS only (compared to AES, XPS, SEM) was feasible to analyze some stain-like carbenoid contamination on the suspected bond pads. The results show that bond pads with low IMC exhibit organic stains and increased surface roughness. The results indicate that the stains are back grind tape residues, which adhere preferentially due to the higher bond pad surface roughness.

In two more examples, the use of ToF-SIMS surface analysis and - imaging analysis is demonstrated to find stains on bond pads and on passivation layers and how to match fingerprint signals helping to identify the source of the contamination.

From the analytical viewpoint, the detection of molecular secondary ions as well as structural fragments with high sensitivity has a big potential for the evaluation of low levels of organic contamination on the sample surface. The identification of molecules and the detection of surface functionalities are commonly applicable to wide variety of materials. These capabilities of ToF-SIMS offer the possibility to identify the root cause of any organic contamination. In the current era of zero failure tolerance, ToF-SIMS can identify the source of organic contamination and therefore prevent reoccurrence which is one important pillar in the today’s quality mind set.

Inkjet 3D printing offers opportunities for additive manufacturing of multi-material electronic devices, such as healthcare sensors, which rely on the interfaces of dissimilar materials to attain their function. We previously demonstrated successful inkjet manufacture of such interfaces and devices with low dimensional materials: graphene/hexagonal boron nitride field effect transistors [1], perovskite (CsPbX₃) nanocrystals / graphene photodetectors [2], and graphene / PEDOT:PSS and silver nanoparticle / PEDOT:PSS heterostructures [3]. However, the performance of these devices strongly relies on the quality of the material interfaces, which are yet to be fully explored and understood; there are few tools and techniques in place to explore these interfaces’ quality, chemistry, and interpenetration, which all define the function on the devices. We explore the interfaces of inkjet-printed heterostructures based on combinations of 2D (graphene, hBN) and 0D (perovskite nanocrystals and metal nanoparticles) materials, and conductive (PEDOT:PSS) and dielectric (PVP, PEG) polymers using complementary Time-of-Flight Secondary Ion Mass Spectrometry and Focused Ion Beam-Scanning Electron Microscopy, revealing infiltration and intermixing between the layers. We examine the effects of the layer composition and deposition/post-deposition parameters on the quality of the interfaces, seeking to establish strategies for control of the interface properties. Polymeric materials, whether as capping agents or as ink formulation components, can strongly influence the interfaces. Our results provide an insight on the composition of inkjet deposited interfaces, which can inform future development of functional heterostructure devices,

References

[1] F. Wang, J.H. Gosling, G.F. Trindade, G.A. Rance, O. Makarovsky, N.D. Cottam, Z. Kudrynskyi, A.G. Balanov, M.T. Greenaway, R.D. Wildman, Inter‐Flake Quantum Transport of Electrons and Holes in Inkjet‐Printed Graphene Devices, Adv. Funct. Mater. (2020) 2007478.

[2] J.S. Austin, N.D. Cottam, C. Zhang, F. Wang, J.H. Gosling, O. Nelson-Dummet, T.S.S. James, P.H. Beton, G.F. Trindade, Y. Zhou, Photosensitisation of inkjet printed graphene with stable all-inorganic perovskite nanocrystals, Nanoscale. 15 (2023) 2134–2142.

[3] G. Rivers, J.S. Austin, Y. He, A. Thompson, N. Gilani, N. Roberts, P. Zhao, C.J. Tuck, R.J.M. Hague, R.D. Wildman, L. Turyanska, Stable large area drop-on-demand deposition of a conductive polymer ink for 3D-printed electronics, enabled by bio-renewable co-solvents, Addit. Manuf. 66 (2023) 103452. https://doi.org/10.1016/J.ADDMA.2023.103452.

For the past two decades, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) imaging has successfully answered various research questions, because it can visualize the spatial distribution of small molecules (< 2000 Da) in 2D with a spatial resolution comparable to that of a light microscope. Dr. Sebastiaan Van Nuffel is presenting various examples of the ongoing research in his group using ToF-SIMS imaging as an invited speaker.

ToF-SIMS imaging is used to simultaneously investigate the elemental composition, the metabolome and the lipidome of tissue sections as well as their interaction with non-native compounds such as drugs or toxins. Although ToF-SIMS allows for label-free detection, ambiguity always remains with regards to structural identification of compounds given the secondary ions of the different compounds present in the sample are all formed together after the impact of the primary ion. Consequently, a typical ToF-SIMS mass spectrum can be considered a summation of the spectra of the individual compounds present and spatial colocation does not necessarily mean that these mass peaks all originate from one compound. Luckily, the creation of ToF-SIMS instruments with MS/MS capabilities makes unambiguous identification finally possible. Regardless, the data generated is very complex, especially in the case of biological systems, and its integration with multivariate analysis techniques for image segmentation and more advanced machine learning approaches for biomarker discovery will be covered as well. In addition, it is difficult to detect large molecules such as intact proteins with a typical ToF-SIMS instrument. It is therefore necessary to integrate ToF-SIMS with other techniques such immunohistochemistry in order to establish a spatially resolved multi-omics atlas. However, there are several issues still hampering its widespread application. In order to become truly competitive with immunofluorescence microscopy, the same field of view needs to be achieved at a similar throughput rate. Ongoing research efforts developing SIMS-IHC methods in combination with novel stigmatic SIMS imaging instrumentation will be discussed.

Finally, as it can observe inorganic and organic compounds with micrometric resolution, ToF-SIMS is also eminently suited for other research than biological and clinical applications such as the investigation of cultural heritage and in particular old paintings. The implications of this research line concerning art authentication in a forensic context will be outlined.

Apolipoprotein E4 (ApoE4) is the strongest risk gene for late-onset Alzheimer’s disease. Growing clinical evidence revealed that dysfunction of systematic metabolism in the brain occurs even twenty years before the onset of evident AD pathological features [1]. Therefore, a better understanding of ApoE4-related pathophysiological mechanisms early and before the onset of Alzheimer’s disease is essential for drug development. Metabolomics is a widely used tool for researching neurodegenerative disease’s related metabolism alteration. However, screening the whole profile of metabolites remains challenging due to the various classes of metabolites that might need different extraction and analysis methodologies[2].

The aim of this study is to investigate the potential mechanism of the risk gene ApoE4 in H4 neuroglioma cells. Metabolomics of ApoE4-carried and wild-type H4 cells was performed by applying a novel workflow composed of OrbiSIMS as a screening tool, followed by targeted LC-MS metabolomics for further confirming polar molecules. Proteins affected by ApoE4 were identified by performing LC-MS-based proteomics.

The data obtained using OrbiSIMS allowed a non-biased overview of metabolic alteration under ApoE4-carried cells. In total, 192 putatively annotated metabolites were detected in our study. PLS-DA (Partial least squares discriminant analysis) was used to identify differential metabolites between two groups. Significant features were selected for pathway and enrichment analysis by filtering with VIP (variable importance for projection) >1 plus FDR (false discovery rate) adjusted p-value < 0.05. Pathway enrichment analysis showed that glycerophospholipid metabolism was inhibited by ApoE4. The alanine, aspartate, and glutamate metabolism was also found to be affected by ApoE4-mediated metabolism disruption. To validate this, we applied polar-targeted metabolomics of LC-MS to exploit these polar compounds, which revealed that the metabolism of taurine and hypotaurine might also be involved in the ApoE4 risk mechanism.

Aside from the metabolomics application of the OrbiSIMS analysis, the chemical filtering (SIMS-MFP) approach [3] allowed us to filter out peptide-related peaks from the OrbiSIMS dataset based on elemental composition. An analysis of the resulting peptide data-sets indicated modification of proteins involved in ApoE4. These suggested differences were then confirmed via proteomics analysis that suggests the nitrogen compound metabolic process, RNA splicing process and translation have been associated with ApoE4-related AD development.

Finally, our metabolomics results by using OrbiSIMS as a screening tool have elucidated the glycerophospholipid dysfunction of H4 neuroglioma cells in the presence of ApoE4, discovering two new potential amino acid pathways that may be involved in Alzheimer’s disease. In addition, SIMS-MFP-aided chemical filtering on the OrbiSIMS dataset and proteomics analysis found the dysfunction of nitrogen compound metabolism and RNA splicing process involved in the risk effect of ApoE4 on Alzheimer’s disease pathology. It suggests that the early monitoring or interference of these molecular functions associated with ApoE4 will help us promote the development of Alzheimer’s disease drugs and prevent the progression of Alzheimer’s disease.

References

1. Frontiers in Cell and Developmental Biology 2021, 9, doi:10.3389/fcell.2021.602887.

2. Nature Methods 2021, 18, 747-756, doi:10.1038/s41592-021-01197-1.

3. Analytical Chemistry 2022, 94, 4703-4711, doi:10.1021/acs.analchem.1c04898.

The viability and adaptability of plants, e.g. to salt stress, relies on the spatial distribution of ions in the liquid medium of the different compartments in the roots, stems, flowers, and leaves. Salinity stress is a major constraint on global plant growth and productivity, impacting various crop plant species, but also roses. According to R. Munns et al. cell exclusion and tolerance of phytotoxic Na⁺ and Cl^- ions are critical to tolerance.[1] Unfortunately, until now spatially highly resolved analysis of ion distribution in hydrated, in situ preserved plant tissue has been challenging using conventional methods.[2] SIMS could bridge the gap, although it needs to address challenges, like vacuum stabilization for high water-content samples.[3]

Although wild roses are not the focus of traditional economic interest, they can hold important ecological and cultural values. In recent decades, Rosa rugosa has displaced the endemic R. spinosissima on the European North Sea coasts of the mainland. Botanists V. Wissemann and A. Kellner suspected the increased site adaptation of R. rugosa due to a stronger tolerance to the salty aerosols of the nearby seawater behind this prime example of man-made fauna biodiversity loss. In classical experiments using gross analytical methods, such as atomic absorption spectrometry of a solution from ashy leaves, they observed reduced accumulation of Na⁺ in leaf tissue of R. rugosa.[4] However such approaches cannot provide sufficient required molecular clues to the different tolerance mechanisms due to their lack of spatial resolution.

In this context, we demonstrated the application potential of SIMS in contributing to the existing knowledge of salinity stress. The complementary combination of mass spectrometry imaging (MSI) and depth profiling, as well as 3D reconstructions provide new insights regarding the different salt tolerance, which only became possible due to the high lateral resolving power. Since SIMS is a high vacuum technique, the high water content and the hydrophobic properties of the leaf cuticle make the sample preparation quite challenging. More over, the very mobile saline ions have to be kept and fixed at their original place. To maintain the leaves in a nearly native state, we employed frozen-hydrated leaf samples from two distinct salt-tolerant rose species, namely R. rugosa and R. spinosissima. These samples were carefully examined following cultivation with artificial sea salt spray solutions.

Both the depth profiles and the cross-sectional ion images qualitatively revealed the lower enrichment of sodium and chloride ions in leaf tissue. Still the cross sectional MSI approach was better suited in delivering spatial localization information. Our MSI approach demonstrated for the first time that R. rugosa exhibits a mechanism that effectively excludes phytotoxic Na⁺ ions from the mesophyll, being essential for fitness. Our findings offer valuable starting points for targeted genomic experiments.

This presentation summarizes our optimized preparational set-up, measurement techniques, and the insights obtained from studying salt tolerance mechanisms in R. rugosa compared to R. spinosissima using SIMS. We also provide valuable insights into common pitfalls and workarounds when employing SIMS in plant physiology research.

Metabolite mass spectrometry imaging has become a valuable tool for localization of plant primary and secondary metabolites within a tissue section. Using Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) imaging, the lateral distribution of various compounds in tomato tissues was determined during development and the change in metabolites due to genetic modifications examined. The lateral resolution of commercially available MALDI-MS imaging instruments of at best 10 µm, allows metabolites to be assigned to specific tissues, such as seed, embryo or fruit skin, but not on a (sub)cellular level. In order to overcome this limitation and better understand processes like production, storage, and transport of secondary metabolites in specific cell types an approach employing secondary ion mass spectrometry (SIMS) using an Orbitrap^TM analyzer was evaluated.

SIMS imaging was performed using a recently developed Hybrid SIMS instrument (IONTOF GmbH), which allows high mass resolution imaging of metabolites and other biological molecules at µm lateral resolution by employing an Orbitrap detector (Q Exactive HF, Thermo-Fisher Scientific) and 20 keV Ar gas clusers. The TOF-SIMS part of the instrument can be operated using Bi-clusters, allowing even sub-µm lateral resolution, but usually accompanied by intense molecule fragmentation.

Here we describe the Orbitrap-SIMS analysis of tomato secondary metabolites, like steroidal glycoalkaloids or flavonoids, inorganic ions, and lipids/fatty acids. Using the Argon gas cluster ion beam in combination with the Orbitrap mass analyzer high mass resolution images were acquired, while TOF-SIMS mode with the Bi- ion beam was used to achieve sub-µm lateral resolution at the moderate mass resolution of the TOF analyzer.

We detected and annotated 10s of compounds/ions in both positive and negative ionization mode, including inorganic ions, lipids, fatty acids, primary metabolites and secondary metabolites at single cell resolution.

Furthermore, we explored the possibility to identify characteristic fragment ions of secondary metabolites directly from the Orbitrap-SIMS imaging run. In contrast to MALDI that does not cause metabolite fragmentation, SIMS using the Bi ion beam leads to strong fragmentation, while using the Argon gas cluster ion beam allows the parallel detection of molecular ions, adducts and characteristic fragments. We analyzed the obtained images using correlation analysis of ion distributions and manual identification of co-localized masses as fragments of steroidal glycoalkaloid molecular ions. Thereby we were able to distinguish between differentially localized molecular ions and assign their characteristic fragments accordingly. This allowed the putative metabolite identification directly from imaging data without performing MS/MS analysis or complementary analysis methods, like LC/MS for compound assignment.

We present here mass spectrometry imaging of plant metabolites using Orbitrap-SIMS at (sub)cellular resolution with high mass resolution & metabolite identification partially using inherent fragmentation.

Kilo-electron volt collision-induced dissociation (keV-CID) enables the compositional identification and structural elucidation of molecules, metabolites and degradation products with 2D/3D visualization by mass spectrometry imaging (MSI). TOF-SIMS tandem MS imaging has been brought to bear for unambiguous molecular visualization in single cell-omics [1], natural product chemistry [2], metabolomics [3,4], surface modification [5], biocompatibility, high performance polymers and composites [6], 2D materials [7], electronic devices [8], catalysis [9], forensic and failure analysis, bio-medicine and pharmaceuticals [10-12]. Here, we will introduce and explore the advantages of surface-induced dissociation (SID) to assist molecular identifications together with the CID spectra. In contrast to the CID which promotes cleavage at every molecular bond, the SID is more subtle in that the bond cleavages result predominantly in the observation of functional group chemistry. While the SID and CID are generated at the same kinetic energy, the molecular energetics are distinct which can have a pronounced effect on the calibration and, hence, the putative peaks used for precursor identification.

References

[1] C.E. Chini, et al, Biointerph. 13 (2018) 03B409.

[2] A. Mikhael, et al, Rapid Comm. Mass Spectrom. (2020) DOI: 10.1002/rcm.8740.

[3] T. Fu, et al, Anal. Chem. 90 (2018) 7535-7543.

[4] T. Fu, et al, Nat. Sci. Rep. 9 (2018) 1928-1938.

[5] G.L. Fisher, et al, Anal. Chem. 88 (2016) 6433-6440.

[6] S. Iida, et al, Bunseki 2018(2) (2018) 52-57 (Japanese).

[7] G.L. Fisher, et al, Microscop. Microanal. 23 (2017) 843-848.

[8] S. Iida, et al, Rapid Comm. Mass Spectrom. (2019) DOI: 10.1002/rcm.8640.

[9] S. Oh, et al, Chem. Mater. 32 (2020) 8512-8521.

[10] A.L. Bruinen, et al, in Imaging Mass Spectrometry: Methods and Protocols, L.M. Cole, Ed. (Springer, 2017) p. 165-173.

[11] N. Ogrinc Potočnik, et al, Anal. Chem. 89 (2017) 8223.

[12] Y. Shi, et al, J. Proteome Res. 18 (2019) 1669-1678.

The continuing development of primary ion beams has arguably been the single most important driver of improvements in secondary ion mass spectrometry (SIMS). This is particularly evident in the analysis of molecular ions, leading to new applications in life sciences.¹ Polyatomic primary ions have greatly extended the sensitivity, depth resolution, and mass range of the technique for molecular analysis.^2,3 While benefits clearly arise from the novel physics associated with keV impact of large clusters on molecular materials, more recently the chemistry has also been shown to play an important role in the SIMS ionisation mechanism(s).^4,5

Here we highlight some of our recent work involving water gas cluster ion beams (GCIBs). We explore the effect of different GCIB chemistry on the secondary ion yields from a range of samples, spanning from pure metal surfaces and single-component drugs to biological tissues. We also attempt to determine the composition of GCIBs containing mixtures of Ar, CO₂, and H₂O, and relate that to SIMS performance to help understand the underlying mechanisms of ion formation.

References:

(1) Yang, J.; Gilmore, I. Application of Secondary Ion Mass Spectrometry to Biomaterials, Proteins and Cells: A Concise Review. Mater. Sci. Technol. 2015, 31 (2), 131–136. https://doi.org/10.1179/1743284714Y.0000000613.

(2) Toyoda, N.; Matsuo, J.; Aoki, T.; Yamada, I.; Fenner, D. B. Secondary Ion Mass Spectrometry with Gas Cluster Ion Beams. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 2002, 190 (1–4), 860–864. https://doi.org/10.1016/S0168-583X(02)00463-9.

(3) Angerer, T. B.; Blenkinsopp, P.; Fletcher, J. S. High Energy Gas Cluster Ions for Organic and Biological Analysis by Time-of-Flight Secondary Ion Mass Spectrometry. Int. J. Mass Spectrom. 2015, 377, 591–598. https://doi.org/10.1016/j.ijms.2014.05.015.

(4) Moritani, K.; Nagata, S.; Tanaka, A.; Goto, K.; Inui, N. Large Molecular Cluster Formation from Liquid Materials and Its Application to ToF-SIMS. Quantum Beam Sci. 2021, 5 (2), 10. https://doi.org/10.3390/qubs5020010.

(5) Lagator, M.; Berrueta Razo, I.; Royle, T.; Lockyer, N. P. Sensitivity Enhancement Using Chemically Reactive Gas Cluster Ion Beams in Secondary Ion Mass Spectrometry (SIMS). Surf. Interface Anal. 2022, sia.7054. https://doi.org/10.1002/sia.7054.

In recent years, the advent of cluster ion beam technology has enabled us to perform high mass molecular ion imaging and organic depth profiling for various types of organic materials. However, when conducting these measurements using commercial time-of-flight secondary ion mass spectrometry (TOF-SIMS) instruments, a significant amount of manual operation is required, leading to considerable effort during the measurements. The primary issue is that optimizing the measurement conditions, such as neutralization and analyzer settings, for each insulating material requires human intervention due to differences in dielectric properties and thickness. Recently, by combining pulsed low-energy electron and pulsed low-energy ion beams, we have successfully achieved fixed neutralization conditions for the majority of insulating materials [1]. Furthermore, we have developed a functionality that allows the computer to optimize the analyzer conditions for each sample, eliminating the need for human intervention. In this presentation, we will introduce our new function and discuss unmanned analysis for insulating samples.

[1] Patent WO2022047190A1.

Nanostructured oxides are coated with self-assembled monolayers of functional organic molecules for various applications, reaching from solar energy conversion to catalysis or medical applications. One example are recently developed "solar capsules", encapsulated dye sensitized solar cells based on titanium dioxide nanotubes.¹ A second example are zirconia nanotubes designed for local, triggered drug release from implant surfaces.² These hybrid materials consist of a porous, inorganic oxide matrix that is modified or filled with organic compounds. Even though these hybrid organic-inorganic nanostructures show good performance, we still lack control and understanding about the depth distribution of the organic molecules within the nanostructures. The analysis of the distribution of the organic compounds within the inorganic porous material is challenging, as a range of artefacts may occur during the sample preparation for analysis, or the analysis itself. To overcome these issues in depth-resolved characterization of hybrid organic-inorganic nanostructures, this study compares the possibilities given by the use of ToF-SIMS depth profiling and ToF-SIMS in combination with cross-section-polishing (CSP) and focused-ion-beam (FIB) cuts.

References

(1) P. Hartwich, S. Naidu Vakamulla Raghu, C. Pritzel, M.S. Killian, “Preparation and characterization of encapsulated dye sensitized solar cells”, submitted.

(2) S. Naidu Vakamulla Raghu, G. Onyenso, S. Mohajernia, M.S. Killian “Functionalization strategies to facilitate multi-depth, multi-molecule modifications of nanostructured oxides for triggered release applications”, Surf. Sci. 2022, 719, 122024, doi: 10.1016/j.susc.2022.122024.

Chemical imaging, e.g. by secondary ion mass spectrometry (SIMS), usually does not need dedicated sample preparation. However, for biological materials vacuum-stability must be achieved, while a close to native fixation is crucial to avoid redistribution or washout of water-soluble ions. Therefore, dedicated cryo approaches have been used in the past and undergo constant further development.

Here, we introduce a novel tool for high resolution imaging and chemical analysis of frozen-hydrated specimen using a cryo-FIB (focused ion beam) platform based on an ultra-high brightness Gas Field Ion Source (GFIS; primary ion species He⁺ and Ne⁺, < 35 keV landing energy range) [1]. Sub-nanometer spatially resolved secondary electron (SE) images with a high depth of field and topographic contrast are predominantly obtained with the finely focused He⁺ ion beam. Sub-surface or volume information at nanometre scale can be retrieved from thin (about 100 nm thickness) samples using the recently developed scanning transmission ion microscopy (STIM) detection system located below the sample [2]. Compositional information, e.g. for identification and subcellular localisation of individual metal nanoparticles embedded in biological matrices can be obtained with the Ne⁺ beam and using the incorporated compact magnetic sector SIMS system with a lateral resolution below 15 nm [3]. Its micro channel plate delay line based continuous focal plane detector features parallel mass detection for each scanned sample pixel over the selected mass range, offering hyperspectral SIMS imaging. Key for cryo-FIB investigations is the integration of a piezo-driven 5-axis cryo-stage along with cryo-capabilities for sample transfers. In combination with dedicated cryo-sample preparation equipment, e.g. a specialised low humidity nitrogen atmosphere glovebox, the cryo-FIB platform is an ideal tool for in-situ correlative studies.

Exemplary data will be presented not only for biological but also other beam sensitive materials like Si-Au core-shell structures and nanoparticles [4].

[1] O. De Castro et al., Anal. Chem. 2021, 93 (43), 14417–14424.

[2] E. Serralta et al., Beilstein J. Nanotechnology 11 (2020), p. 1854.

[3] J.-N. Audinot et al., Rep. Prog. Phys. 84 (2021) 105901

[4] This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 720964 and was supported by the Luxembourg National Research Fund via the projects INTER/DFG/19/13992454 and FNR CORE C21/BM/15754743.

The high demand for portable energy storage has boosted Li-ion battery research in recent years. Special focus has been given to the improvement of specific capacity, safety and the use of environmentally friendly components. There is a continuous effort to correlate electrode structure, morphology and chemical composition with behaviour, performance and failure mechanisms; however, many fundamental aspects have not yet been fully described [1,2]. Among the analytical techniques, Secondary Ion Mass Spectrometry (SIMS) is particularly suitable for analysing the electrodes due to the excellent sensitivity and capability to detect all elements and their isotopes. Its surface-sensitivity makes it appropriate for investigating electrodes and their interfaces (e.g. Solid Electrolyte Interphase)[3].
In recent years, a FIB-SEM-SIMS system has been developed to combine the advantages of high-resolution imaging by SEM and analytics of a magnetic sector SIMS in a single instrument [4]. With a SIMS spatial resolution down to 15 nm, this microscope is a powerful tool for correlative microscopy. The great added value of this platform includes the Ga+ FIB in-situ sample preparation avoiding sample transfer to another system and thus minimising the risk of contamination of air-sensitive electrode components.
In this work we survey graphite electrodes before and after cycling, developing analytical protocols to study surface and internal structure. A combination of in-situ sample preparation with depth profiling and SIMS imaging was developed to probe both interfaces of the electrode and provide in 3D the elemental and isotopic distribution on surface and in volume. Our results demonstrate the capability of a single instrument to investigate the morphology and composition of battery components with nanoscale spatial resolution and high sensitivity, addressing environmental contamination issues of electrode components.
This work was co-funded by the Luxembourg National Research Fund (FNR) through the grant INTER/ANR/21/NANOLIT.
References:
[1] Gauthier, M., Carney, T. J., Grimaud, A., Giordano, L., Pour, N., Chang, H. H., ... & Shao-Horn, Y. (2015). The journal of physical chemistry letters, 6(22), 4653-4672.
[2] Asenbauer, J., Eisenmann, T., Kuenzel, M., Kazzazi, A., Chen, Z., & Bresser, D. (2020). Sustainable Energy & Fuels, 4(11), 5387-5416.
[3] Waldmann, T., Iturrondobeitia, A., Kasper, M., Ghanbari, N., Aguesse, F., Bekaert, E., ... & Wohlfahrt-Mehrens, M. (2016). Journal of The Electrochemical Society, 163(10), A2149.
[4] O. De Castro, J.-N. Audinot, H. Q. Hoang, C. Coulbary, O. Bouton, R. Barrahma, A. Ost, C. Stoffels, C. Jiao, M. Dutka, M. Geryk, T. Wirtz, Analytical Chemistry, 94(30), 10754-10763 (2022).

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool for biological investigation as it can simultaneously detect various biomolecular species across length scales from cells to tissues, thanks to its high sensitivity coupled with high spatial resolution. ToF-SIMS has a role in spatial biology as a high-resolution multi-omic imaging platform that can detect elemental ions and metabolites, including intact lipids, label-free with subcellular spatial resolution without the need for matrix application¹. However, the direct label-free detection of intact peptides and proteins on tissue or within a cell is not currently feasible with a typical ToF-SIMS instrument. Multiplexed IHC techniques using tagged antibodies offer targeted protein imaging as it labels individual available proteins with reporters detectable with different MSI platforms. With our ToF-SIMS instrument and using metal-labelled antibodies, it is thus possible to detect multiple metal tags and thus multiple proteins in one imaging experiment. Here, we aim to use multiplexed ion beam imaging (MIBI™, IonPath, Inc.)² using metal conjugated antibodies to visualize protein expression on fresh frozen (FF) tissue along with complementary metabolite and lipid information on adjacent sections. We also describe the use of our state-of-the-art ToF-SIMS (PHI NanoTOF II) with tandem MS capability equipped with a liquid metal ion gun, C₆₀ ion gun, Ar cluster ion gun³.

Flash-frozen tissue blocks were sectioned with a thickness of 12 mm using a Leica cryostat microtome at -20°C. Serial sections from same tissue block were obtained and collected on clean indium tin-oxide coated glass slides. Prior to ToF-SIMS imaging, the tissue sections were dried using a vacuum desiccator for at least 3 hours. We were able to image elemental ions, metabolites and lipids in fresh-frozen tissue sections using a Bi liquid metal ion gun. We show complimentary images from adjacent serial sections using optical microscopy, standard histological staining (H&E staining), and ToF-SIMS imaging. In the next step, we will perform SIMS-based IHC where adjacent fresh frozen sections will be incubated with metal-conjugated antibodies.

Ultimately, we aim to develop a ToF-SIMS-based multi-omics pipeline to validate spatially resolved protein detection and have complementary metabolomic and lipidomic information on the same fresh frozen tissue sample. Correlative multi-omic imaging paired with same tissue architecture provides a way to investigate intermolecular mechanisms in biological tissues such as in disease progression and diagnosis in a single frozen tissue section.

References:

1 M. J. Taylor, J. K. Lukowski and C. R. Anderton, J Am Soc Mass Spectrom, 2021, 32, 872–894.

2 M. Angelo, S. C. Bendall, R. Finck, M. B. Hale, C. Hitzman, A. D. Borowsky, R. M. Levenson, J. B. Lowe, S. D. Liu, S. Zhao, Y. Natkunam and G. P. Nolan, Nat Med, 2014, 20, 436–442.

3 G. L. Fisher, A. L. Bruinen, N. Ogrinc Potočnik, J. S. Hammond, S. R. Bryan, P. E. Larson and R. M. A. Heeren, Anal Chem, 2016, 88, 6433–6440.

Human papillomavirus (HPV) infection causes approximately 5% of all new cancer cases. HPV types 16 and 18 causemore than 70% of high-grade cervical pre-cancers and 340,000 women die globally per year [1]. Moreover, HPV-positive (HPV⁺) oropharyngeal squamous cell carcinoma (OPSCC) has one of the most quickly ascending incidences in developed countries [2]. Only 28% of the HPV+ OPSCC cases are diagnosed early enough due to the lack of observed precursor lesions. Diagnostic methods that rely on histology, cytology, and HPV-DNA-based have certain limitations (e.g. non-quantitative) so there is a need to improve the imaging of oral lesions at a molecular level and meet the clinical need of identifying new disease-specific biomarkers. During the past two decades, imaging mass spectrometry (IMS) has arisen as a powerful tool for studying biological systems, because it provides label-free molecular characterization [3]. Here, we aim to develop a mass spectrometric image data analysis workflow for the identification of markers for PV-induced tumor tissues using a mouse papillomavirus (MmuPV1) model system [4]. This is followed up by tandem mass spectrometry measurements to unambiguously identify all marker species, allowing us to gain further insight into its role in HPV pathogenesis.

This proof-of-concept study uses IMS and a supervised machine classifier to identify novel biomarkers in PV-induced tumors. Flash-frozen skin tissue blocks of MmuPV1-infected [4] and control mice (N=5/group) were sectioned with a thickness of 12 mm using a Leica cryostat microtome at -20°C and thaw-mounted on conductive ITO-coated glass microscope slides. The analyzed areas were chosen based on matching with adjacent tissue sections, which were H&E stained. Prior to SIMS imaging, the tissue sections were freeze-dried for >2h. ToF-SIMS analyses were performed using a PHI nanoTOF instrument (Physical Electronics, USA) equipped with a Bi liquid metal ion gun. 30 keV Bi₃⁺ primary ions were used in all measurements. 500 μm × 500 μm images were rastered with 512 × 512 pixels. Forty frames were collected for each image with a cycle time allowing a 0–1850 Da mass range. Low-energetic 20 eV electrons of the flood gun compensated sample charging. Both positive and negative polarity ToF-SIMS images were acquired from 5 sample locations for each mouse, resulting in 100 image datasets. The data analysis workflow consisted of segmentation based on principal component analysis and K-means clustering in order to identify the hypodermis, the dermis, and the epidermis; allowing for a pair-wise comparison of infected and non-infected tissue layers. Prior knowledge of histopathologically identified tissue types of MmuPV1-infected and control mice then allows a random forest classifier to identify potential markers.

This work demonstrates the perspective of a supervised machine classifier on ToF-SIMS image data for the discovery of PV-induced tumor biomarkers, which subsequently could lead to new methods for early diagnosis of HPV⁺OPSCC.

1. D. K. Gaffney et al. Gynecol. Oncol. 2018, 151, 547.
2. M. Lechner et al. Nat. Rev. Clin. Oncol. 2022, 19, 306.
3. S. Van Nuffel et al. Anal. Chem. 2020, 92, 12079.
4. J. Hu et al. Viruses 2017, 9, 246.

Retrieval of fingermark evidence from bullet casings is an area of major difficulty for forensic scientists. This is due to both the physical conditions, e.g. high temperature, pressures and large friction forces, that are experienced by the bullet casings during firing and the techniques used to develop and image the fingermarks. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a highly sensitive surface analysis technique that can map different chemicals on a surface and has shown great promise for the retrieval of fingermarks from flat metallic surfaces. We have developed a high precision ultra-high vacuum (UHV) rotation stage that allows the surface of cylindric bullet casings to be imaged using ToF-SIMS. Experiments were performed over a period of seven months to investigate how fingermarks deposited on the surface of cylindrical bullet casing (Webley MkII round) change over time. The ToF-SIMS analysis was performed by analysing a thin strip along the length of a casing before rotating it by a few degrees and analysing a new strip. The process was repeated until the entire casing has been imaged. Obtained images were then stitched together. ToF-SIMS images of the fingermarks were found to show clear ridge and sweat pore detail on samples that showed no evidence of fingermarks when developed using cyanoacrylate fuming and subsequent staining with Basic Yellow 40 (BY40) dye. ToF-SIMS images were also compared to fingermarks that had been deposited onto flat paper surfaces using ink to assess the effects of the curvature of the cylindric casings on the morphology of fingermarks. The distortions caused by differences in surface curvature were found to be within acceptable limits.

Batteries play a pivotal role in the ongoing energy transition from fossil fuels to sustainable sources by efficiently storing energy. Among various battery types, Li-ion batteries have gained significant prominence in electric vehicles and consumer electronics, primarily attributed to their high energy density.

Therefore, the demand for Cathode Active Materials (CAMs) with a high specific capacity is steadily growing, where nickel rich layered oxides are already promising candidates. Specific capacity of nickel-rich layered oxides surpasses other classes of cathode active materials (CAMs), such as lithium-manganese rich spinels and lithium iron phosphate olivine phase, demonstrating their superior performance. However, the higher nickel content in these layered oxide materials also makes them more sensitive to moisture, particularly water.

Following the synthesis process, residual lithium salts on the CAMs surface, which have a negative effect on their electrochemical performance. Consequently, the synthesis residuals are removed during post-processing through a water washing step. Unfortunately, the interaction between the CAM and water during this washing step leads to an exchange of H⁺ and Li⁺-ions, thereby reducing the available lithium inventory and thermostability of the CAM.

In addition to the washing step, the water-based thin film casting of electrode sheets is gaining increased attention for its potential to eliminate the use of NMP (N-Methyl-2-pyrrolidone) in battery manufacturing processes, thereby enhancing their environmental friendliness. Moreover, during the water-based thin film coating process, there is an exchange of H⁺ and Li⁺-ions in the cathode active material.

This study focuses on the characterization of H⁺-Li⁺-exchange between water and nickel rich CAM using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). To achieve a better depth resolution with the ToF-SIMS, a flat nickel- rich layered oxide model system is prepared and washed with deuterated water. The ToF-SIMS technique is then employed to investigate the change in the surface structure and the depth of H⁺ and Li⁺ exchange. The main objective of this research is to determine the kinetics of the H⁺-Li⁺ exchange process for nickel-rich CAMs. Enhancing our understanding of the H⁺-Li⁺-exchange process can be leveraged to optimize processing parameters for synthesizing nickel-rich cathode active materials and water-based film coating of cathode electrodes.

Skin ageing, characterized by wrinkles, hyperpigmentation, and the loss of elasticity is a multifaceted process that can be intrinsic or extrinsic in nature³. Vitamin C (ascorbic acid) is a powerful antioxidant, commonly used in skincare creams to tackle skin ageing by reducing reactive oxygen species (ROS), preventing the suppression of collagen production and promoting the transcription of procollagen I and III genes in cells⁴. The topical use of this compound is currently restricted, due to its instability and susceptibility to be oxidised⁵. Information regarding the depth and lateral distribution of active agents such as vitamin C would be highly informative and could help optimise skincare systems. However, this information is very difficult to ascertain, especially in-vivo.

Mass spectrometry Imaging techniques, such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and 3D OrbiSIMS are rapidly gaining popularity in the characterisation of the molecular structure of the skin and its integrity, especially the barrier layer known as the stratum corneum^1,2. These techniques offer relatively high mass and spatial resolving power, with the possibility of exploring the permeation of cosmetic actives as a function of depth.

In this research, the permeation and lateral distribution of vitamin C, from a commercially available product, through the stratum corneum was established using ToF-SIMS and OrbiSIMS. A study was performed to understand the impact of exposure time using both ex-vivo porcine skin and in-vivo human tape strips. It was observed that permeation was the deepest at 24 hours, whilst still being localised at the surface of the stratum cornuem after 4 and 8 hour exposure times. The lateral distribution of vitamin C was demonstrated as being heterogenous, localised in pools of high intensity through all the layers of the stratum corneum. Both the ToF-SIMS and OrbiSIMS analysis were capable of detecting the vitamin C within the skin, however, the OrbiSIMS demonstrated a significantly enhanced sensitivity.

1. P. Sjövall, S. Gregoire, W. Wargniez, L. Skedung and G. S. Luengo, Int J Mol Sci, 2022, 23, 13799.

2. N. J. Starr, M. H. Khan, M. K. Edney, G. F. Trindade, S. Kern, A. Pirkl, M. Kleine-Boymann, C. Elms, M. M. O’mahony, M. Bell, M. R. Alexander and D. J. Scurr, , DOI:10.1073/pnas.

3. K. Biniek, J. Kaczvinsky, P. Matts and R. H. Dauskardt, J Dermatol Sci, 2015, 80, 94–101.

4. Y. C. Boo, Antioxidants, 2022, 11, 1663.

5. N. J. Starr, D. J. Johnson, J. Wibawa, I. Marlow, M. Bell, D. A. Barrett and D. J. Scurr, Anal Chem, 2016, 88, 4400–4408.

Characterisation of peptides and proteins within a biological specimen is of great importance for clinical proteomics to improve disease classification and to identify new therapeutic agents. Previously, studies of these biomolecules with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) has been limited due to the chemical damage caused by the monoatomic or small cluster beams to the analyte [1]. However, with application of the large gas cluster beams, the detection of these biomolecules is now feasible since they impact the surface as a single entity [2,3,4]. This results in a very gentle ion emission with a consequence of very low fragmentation of the emitted molecular ion.

Here we show with water gas cluster ion beam (H₂O)_n, small proteins can now be detected as intact multiply charged species; whereas with (Ar/CO₂)_n beam these ions are not produced or the formation of fragments is favoured. We also explore the effect of sample preparation and analysis conditions on the formation of multiply charged ions of a peptide/protein. An improved sensitivity for 2+, 3+ and 4+ ions of peptides/proteins will provide a new route of detection of large proteins by SIMS.

References

[1] B.J. Garrison, Z. Postawa, ToF-SIMS: Materials Analysis by Mass Spectrometry 2^nd Ed, 2013.

[2] S. Sheraz, I. B. Razo, T. P. Kohn, N. P. Lockyer, J. C. Vickerman, Anal. Chem. 87, 2367 (2015).

[3] A. M. Kotowska, G. F. Trindade, P. M. Mendes, P. M. Williams, J. W. Aylott, A. G. Shard, M. R. Alexander, D. J. Scurr, Nat. Commun. 11, 5832 (2020).

[4] H. Tian, S. Sheraz née Rabbani, J. C. Vickerman, N. Winograd, Anal. Chem. 93, 7808 (2021).

Perovskite oxides are widely used in different solid oxide fuel cell (SOFC) components. SOFCs are highly efficient devices that can generate energy by electrochemically combining hydrogen and other fuels with oxygen. They are composed by an assembly of thin ceramic layers (cathode/electrolyte/anode). The operation of SOFCs involves the oxygen reduction at the porous cathode, transport of oxygen ions throughout the dense electrolyte, and the oxidation of the fuel at the porous anode. Among the perovskite oxides used in SOFC, La_1-xSr_xGa_1-xMg_xO_3-d (LSGM) is one of the most promising electrolyte materials due to its high ionic conductivity. Nevertheless, pure LSGM phase is really hard to obtain and there is a wide discrepancy in the literature regarding the secondary phases formed under different sintering conditions. Bulk characterization techniques such as Energy Dispersive Spectroscopy-Scanning Electron Microscopy (EDS-SEM) and X-ray diffraction (XRD) are generally used for identifying these secondary phases, which might yield misleading conclusions since the volume occupied by these secondary phases is usually smaller than the volume analyzed by using these bulk techniques. In this regard, surface analysis techniques such as TOF-SIMS can provide valuable complementary information for identifying the secondary phases present in LSGM samples.

This work aims at studying the elemental distribution on the surface of LSGM pellets sintered at different temperatures. Commercial (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3-d (Praxair) and La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-d (Fuel Cell Materials) powders were uniaxially pressed and thermally treated in air at different temperatures within the 1200-1400 ºC range. The surface chemical composition of the pellets was investigated by TOF-SIMS imaging and depth profiling. In addition, the crystallographic phases present in each sample were identified by XRD while the bulk chemical composition was analyzed by EDS/SEM. Even though the effect of electrical charging and the topography of the samples can hinder the interpretation of TOF-SIMS data, the performed analysis demonstrate that TOF-SIMS is a useful complementary technique for a better interpretation of XRD and EDS/SEM results and for the understanding of LSGM phase formation mechanisms.

Pulsed laser deposition (PLD) is one of the most common techniques to grow oxide thin films with a complex composition. However, the congruent transfer of the target composition to the film can be a difficult task. This is particularly noticeable when depositing materials composed of elements with a large mass difference, which can lead to a significant deficiency of light elements in these films, such as Li. Given that many Li-containing materials are very sensitive to the exposure to air due to the formation of lithium carbonate or lithium hydroxide, it is essential to use in situ tools to gain a direct insight into growth properties of as-deposited films.
An ultra-high vacuum PLD-chamber equipped with various analytical techniques, including optical emission spectroscopy, plasma imaging, plasma mass spectrometry and secondary ion mass spectrometry (SIMS), has been designed to perform comprehensive studies on the chemical composition of the ablation plume, energetics of the plasma, time-resolved expansion profile of chemical species in the plume and the chemical composition of in situ grown films. We investigated the laser induced plume dynamics of Li_xMn_yO_z and analyzed in situ and ex situ grown films using SIMS depth profiling. The difference in the elemental distribution as a function of thickness of the Li_xMn_yO_z films revealed changes at the surface upon air exposure. In situ SIMS was also used to characterize films grown under different background pressures (10^-8 to 10^-1 mbar of O₂), and results are correlated to differences observed by plasma imaging like differences of the Li and LiO distributions in the plasma plume. In addition, in situ SIMS was carried out at different stages of the PLD process, which revealed differences in the distribution of the elements throughout the film upon annealing.

ToF-SIMS is an excellent method to observe changes in lipids, which are known to play an important role in neurodegenerative diseases. The introduction of an argon cluster ion beam into ToF-SIMS has made it more favorable for observing higher-mass lipids. However, the ability of ToF-SIMS to identify lipids was still limited. To identify lipids, MS/MS capabilities have recently been introduced to ToF-SIMS. To obtain MS/MS spectra, the orbitrap mass spectrometer with a long-pulse argon cluster ion beam is used. In this study, mass spectra and images were obtained from the mouse brain tissue using pulsed argon cluster ion beam in ToF-SIMS. ToF-SIMS mass spectra obtained with a pulsed argon cluster ion beam were compared to orbitrap mass spectra obtained with a long-pulsed argon cluster ion beam. From this results, we can see that there is no significant difference between the mass spectra obtained with ToF-SIMS and OrbiSIMS. The OrbiSIMS spectra showed better mass resolution and mass accuracy. MS/MS spectra obtained using the orbitrap were compared to LC-MS/MS spectra used as a golden standard, and the MS/MS spectra obtained from the two instruments were similar.

ToF-SIMS is a surface chemistry analysis that provides information at the molecular level on the surface of a sample. In the field of polymers, it has been utilized for composition analysis and copolymer component discrimination using backbone-specific repeat units [1]. However, due to the complexity of ToF-SIMS data, distinguishing chemically similar types of polymers remains a challenge. In particular, for various materials that share a backbone in the hydrocarbon family, such as plastics, it is still difficult to distinguish them by their surface mass spectra. It has been reported that SOM methods can be applied to ToF-SIMS data for polymer classification and protein orientation analysis [2,3].

We applied machine learning techniques to spectral data of plastic samples and their raw materials to explore various ways to distinguish of similar structures. In particular, we analyzed the features that contributed to the distinction of each plastic, i.e., the main unit components, through feature extraction. We propose a machine learning method to extract features with optimal classification performance in microplastic classification. Through this, we were able to successfully distinguish five types of plastics and present the features of each plastic.

The development of new polymeric materials with ever more micro- to nano-sized structures is gaining significant interest in different fields, such as optical devices, biology, molecular electronics with a large focus in the battery field. The versatility of the polymers can be specially seen in the battery field where polyelectrolytes have been applied as both solid electrolyte materials (polymer electrolytes. Poly(ionic) liquids, single ion conductors, etc.) and as binders for high-capacity anodes [1]. Moreover, to further optimize the electrochemical performances of new-generation batteries, an ever-increasing effort to employ micro/nanophase separated polymer materials or nano particles containing composites has been observed in recent years. However, the use of such new polymer materials led to an enormous challenge in terms of their characterization, microscopy, chemical micro- and nano-analysis. Therefore, the development of new advanced characterization techniques providing excellent spatial resolution and high-sensitivity elemental information is of upmost importance.

A multimodal imaging instrument combining the Helium Ion Microscope (HIM) and Secondary Ion Mass Spectrometry (SIMS) has been developed at LIST allowing for in-situ correlative microscopy. The system combines the ZEISS ORION NanoFab HIM using a Gas Field Ion Source (GFIS), and a magnetic sector SIMS system [3]. During secondary electron (SE) imaging, He⁺ and Ne⁺ scanning can achieve resolutions down to 0,5 nm and 2 nm, respectively, while in SIMS imaging the instrument has the capacity to reach lateral resolutions down to 15 nm [4]. On top of 2D and 3D images, mass spectra and depth profiles can also be acquired on this instrument.

Here, we will present the preliminary results obtained on polymer samples, highlighting the advantage of using light ions (i.e., He⁺ and Ne⁺) in SIMS to provide high spatial resolution information and to reduce the fragmentation of the polymer material in DC mode. A related methodology was developed on thin films samples representing blends of immiscible polymers, namely of polystyrene and poly(methyl methacrylate)[5]. A special focus was put on the SIMS fragment identification, phase domain distribution and phase separation mechanism.

This work was co-funded by the Luxembourg National Research Fund (FNR) through the grant INTER/ DFG/22/16558792/MINABATT

References

[1] A. M. Wilson., G. Zank, G. Eguchi, W. Xing, & J. R. DahnIn J. Power Sources 68:195–200 (1997).

[2] D. Deng, (2015). Energy Science and Engineering Vol. 3, Issue 5, pp. 385–418 (2015).

[3] J. N. Audinot, P. Philipp, O. De Castro, A. Biesemeier, Q. H. Hoang, T Wirtz, Reports Prog. Phys. 84, p.105901 (2021).

[4] D. Dowsett, T. Wirtz, Analytical Chemistry, 89(17), 8957–8965 (2015).

[5] L. Kailas, J. N. Audinot, H. N. Migeon, & P. Bertrand, Composite Interfaces, 13(4–6), 423–439 (2006).

Sporadic Parkinson’s disease (PD) is a neurodegenerative disease affecting mostly the elderly. One characteristic change observed in the brain during aging and PD is the neuronal accumulation of iron and other reactive metals in substantia nigra (SN) and locus coeruleus (LC), mainly occurring in cytoplasmic stores and so-called neuromelanin (NM) organelles. Several spectroscopic studies (e.g. Zecca et al PNAS 2004; Biesemeier et al J Neurochem 2016) investigated the role of quantitative and molecular changes of metals in the SN during aging and disease progression. However, no studies were performed using high lateral resolution techniques for subcellular (re)distribution analyses or were concerned with the elemental composition of LC and its involvement in PD.

This work studies the subcellular and even sub organellar distribution of toxic metals in the NM-containing organelles (having melanin, lipid and protein-based partitions of < 100 nm in diameter) of LC in aging and PD using established and novel analytical approaches based on secondary ion mass spectrometry (SIMS).

Analyses are performed on available resin-embedded human LC tissue prepared for analytical transmission electron microscopy (aTEM). 100 nm thin epoxy sections were first quantitatively analysed using aTEM and then by CAMECA NanoSIMS 50 (caesium and oxygen beams), with the ability for isotopic identification, highest sensitivity and mass resolution, and a lateral resolution down to 50-100 nm for chemical imaging. Sub organellar distribution of metals in NM-containing organelles is addressed on selected samples using FIB-SIMS (gallium, helium and neon primary ion beams, lateral resolution < 20 nm for SIMS; < 1 nm for secondary electron (SE) imaging) developed at LIST. TEM like ultrastructural investigation is possible on the so-called npSCOPE, a novel cryoFIB-STIM-SIMS platform based on ultra-high brightness Gas Field Ion Source (GFIS; Primary ion species He and Ne, Anal Chem. 2021, 93 (43), p14417) with SE, SIMS and scanning transmission ion microscopy (STIM) detectors (Beilstein J. Nanotechnology 11 (2020), p1854). The same instrument will be used in future to perform respective analyses on frozen-hydrated brain samples to minimize preparation artefacts.

Here we present first results for the chemical identification of melanin-based and cytoplasmic metal storage sites for sodium, aluminium, calcium and iron in nor-adrenaline neurons of LC. A semi-quantitative FIB-SIMS approach is formulated where a sample is imaged first at high resolution using SE or STIM imaging to identify the region of interest and then SIMS maps are acquired with a field of view of about 5 – 70 µm for the chemical identification and metal storage of particular areas in the tissue with higher sensitivity then aTEM. Future investigations on cryopreserved specimen with the cryoFIB-STIM-SIMS platform or cryoTOF-SIMS for molecular analyses will give a more detailed view on the role of metal loading of NM in brain aging and Parkinson’s disease that could help in analysing biological samples very close to their native state.

This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 720964 and was supported by the Luxembourg National Research Fund via FNR CORE C21/BM/15754743 and INTER/DFG/19/13992454.

Chronic sleep deprivation (CSD) is a detrimental condition leading to enhanced oxidative stress, which is closely associated with the development of various diseases including cardiovascular disorders, cognitive dysfunction, metabolic syndrome, and impaired reproductive activity. Considering zinc (Zn) is the second-most necessary trace element playing an important role in the regulation of anti-oxidative defense network and initial stages of spermatogenesis and fertilization, the primary objective of this study is to determine whether the testicular expression of Zn would significantly be altered following CSD. Adult Wistar rats subjected to three cycles of CSD with each cycle consisting of five consecutive days of total sleep deprivation followed by a two-day break were used in this study. The testicular level and intensity of Zn were determined by the time-of-flight secondary ion mass spectrometry (TOF-SIMS). The functional significance of Zn was evaluated by the extent of oxidative level, the expression of Cu/Zn superoxide dismutase (Cu/Zn SOD), and the sperm mobility. Results indicated that in normal untreated rats, fine sperm motility with extensive high levels of Zn, abundant expression of Cu/Zn SOD, and low oxidative stress was detected in the testicular tissues. However, following CSD, a significant reduction of Zn expression, decreased activation of Cu/Zn SOD, and excessive increase of oxidative stress were all observed in testicular samples. Reduced expression of Zn coincided well with the substantial decline of sperm motility. Based on these findings, the present has provided for the first time that impairment of testicular Zn expression, together with reduced activation of Zn-related anti-oxidative enzymes may serve as the underlying mechanism(s) for the pathogenesis of CSD-induced reproductive disability.

In its current state, the fashion industry is unsustainable. Sustainability issues include incineration and landfill disposal of clothes and microplastic shedding during washing.

Fabric care products aim to alleviate these issues by extending the lifetime of clothes. Biologically based formulations investigated herein have been evaluated previously with bulk applications tests to demonstrate product performance benefits.

However, little is known about their mechanisms of action. To investigate these, and ultimately develop new improved fabric care products, biomolecule-fabric interactions have been studied with Atomic Force Microscopy (AFM), Secondary Ion Mass Spectrometry (SIMS), and Dynamic Mechanical Analysis (DMA).

A greater degree of biomolecule permeation in natural versus artificial fabrics, surface coating homogeneity, presence following consumer washing, and biomolecule mode of action of reduction of inter-fibre fiction is presented.

The application of SIMS to biological materials has expanded substantially in the last decade ⁽¹⁾. There have been important advances in technology including the use of a wide range of gas cluster ion beams for analysis using argon ⁽²⁾, water / CO₂ mixtures ⁽³⁾ and water ⁽⁴⁾. In addition, new analysers have been developed for improved biological analysis including the J105 ⁽⁵⁾ (Ionoptika, UK) and the OrbiSIMS ^(6,7) (Hybrid-SIMS, IONTOF GmbH, Germany) amongst others. SIMS now allows molecular imaging of complex biological samples ranging from cells to tissues. To improve repeatability and determine reproducibility between laboratories with varying instrument configurations there is a need to define and establish a biologically relevant biomimetic sample for pharmaceutical and small molecule analysis.

In this study, we present a step-by-step approach for sample preparation of a biomimetic reference material composed of doped tissue homogenate from rat liver using a protocol developed by GlaxoSmithKline for MALDI MS ⁽⁸⁾. The resulting material was characterised using ToF-SIMS (Bi₃⁺ analysis beam) and OrbiSIMS (Ar₂₅₀₀⁺) depth profiling. The spiking of different drugs in the resulting material is used to study the influence of matrix effects on detection sensitivity ⁽⁹⁾, limit of detection and calibration for quantification. This study evaluates the possibility of using this reference material for a future VAMAS interlaboratory comparison suitable for dual beam and single beam analysis instruments.

Reference:

(1): D. Schaumlöffel J. Anal. At. Spectrom., 2020,35, 1045-1046

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Aluminium-lithium alloys are extensively used in aerospace applications due to the improved properties the addition of Li has on the Al alloy system. Low density alloys are extremely important in aerospace applications due to the increasing demand to reduce fuel consumption thereby reducing greenhouse gas emissions and save cost. For every 1 at% of Li added to the aluminium alloy, the density is reduced by 3%. The distribution of Li and its precipitates have a major effect on the properties of the alloy. Although Al-Li alloys have been in development since the 1920’s, there are still challenges associated with their production, for example when Al-Li alloys are cast the Li does not remain evenly distributed throughout the casting due to its low density. Current research is investigating if additive manufacturing can generate a uniform distribution of Li in these alloys. However, it is analytically very challenging to spatially localise the Li distribution with traditional techniques such as with energy dispersive X-ray spectroscopy in a scanning electron microscope. As it is difficult to determine the Li distribution it is hard to understand the role it plays in alloy strengthening in conventionally produced and additively manufactured alloys.

In this project high spatial resolution secondary ion mass spectrometry (NanoSIMS 50L) and Electron Probe Microanalysis (EPMA) with a wavelength-dispersive soft X-ray emission spectrometer (WD-SXES) are used to characterise Wire + Arc additive manufacturing (WAAM) produced Al-Li alloys. The results show that in the as-produced alloy the precipitates are highly complex containing a wide range of elements that have co-precipitated. This presentation will show how the NanoSIMS is able to map Li at high lateral resolution which is necessary as the Li-containing precipitates are less than a micron in size. However, the exact type and composition of the complex precipitates are yet to be determined and further complementary EPMA work is required to achieve this. The next stage of this project is to combine the NanoSIMS and EPMA WD-SXES data to quantify the Li in both the precipitates and matrix.

The chemical structure and morphology of carbonized bio-based materials are not yet understood. Various biomaterials have been utilized to prepare porous materials by carbonization, which is used for different environmental remediation applications, including air filtration and water treatment. In this work the effect of pyrolysis temperature (600–1000 °C, no oxygen-atmosphere) on chemical structure, porosity and morphology of date seeds was investigated. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) were used to study the changes in chemical compositions at the molecular level of the carbonized date seeds. The TOF-SIMS study revealed a complex mixture of compounds inhomogeneously distributed on the carbonized surface, and showed that fatty acids disappear quickly as a result of the heat-treatment. Both TOF-SIMS and XPS showed that metal oxides (especially potassium) accumulate during heating and the degree of aromaticity is observed to increase. The chemistry and morphology were shown (to some degree) to be controllable, which makes the material a promising candidate for developing a cheap porous adsorbent from date seeds.

Cornea, the outermost transparent layer of the eye, protects the eye from the external environment and maintains a proper vision. It is composed of three cellular layers, including the epithelium, 500 µm-thick stroma, and endothelium, separated from each other by two non-cellular collagen-based Bowman’s and Descemet’s membranes. The stroma represents ~90% of the cornea’s volume and constitutes a resilient collagen fibril-keratocyte architecture for the cornea ensuring optimal visual acuity. Untreated dysfunction of the cornea causes Fuch’s dystrophy, the dry eye syndrome, and keratitis that may lead to the blindness. The exploitation of modern in vitro and in vivo models for the corneal disease treatment suffers from experimental, ethical, and economical shortcomings, which necessitates developing human cornea-on-a-chip (CoC) devices allowing rapid and high-throughput sensing and drug screening. Comprised of 3D artificial biomaterial organoids or cultured biomaterial-human organ hybrids, well-defined modern lab-on-chips mimic molecular complexity, fluid dynamics, and physiological behaviour of real tissues or organs.

Here we present the photocrosslinking-based fabrication of a gelatin methacryloyl (GelMA) hydrogel lithographic CoC, and its analysis by time-of-flight secondary ion mass spectrometry (ToF-SIMS), as a benchmark for future studies involving seeded cells and drug diffusion in the hydrogel matrix. In the process, we compared 2D images, positive and negative SI mass spectra, and depth-profiles of GelMA hydrogel with ex vivo corneal sections, using typical collagen-derived species and keratocyte-membrane phospholipids as markers. ToF-SIMS of the GelMA hydrogel and the tissue confirmed the majority of NH^-, CN^-, CNO^-, C₃N^- and CH₂N⁺, CH₄N⁺, C₂H₄N⁺, C₂H₆N⁺, C₃H₆N⁺, C₄H₈N⁺, C₃H₈N⁺ in the samples. Moreover, the tissue spectra revealed signals of keratocyte plasma membrane-derived choline (C₅H₁₄NO⁺), phosphocholine (C₅H₁₅PNO₄⁺), phosphatidylcholine (C₄₀H₈₁NO₈P⁺), and fatty acids (C₁₆H₃₁O₂^‑, C₁₈H₃₃O₂^-, C₁₈H₃₅O₂^-). X-ray photoelectron spectroscopy measurements confirmed the atomic contents in artificial and native cornea samples, whereas atomic force microscopy imaging and nanoindentation studies revealed their broad ranges of elasticity (0.03-3 MPa), as expected from the literature data. Future ToF-SIMS experiments will involve in-chip seeded keratocytes as well as epi- and endothelial cells. Finally, off- and on-a-chip ToF-SIMS-based study of drug diffusion will be executed to validate the cornea-on-a-chip as an efficient model for high-throughput drug screening applications.

Anatase TiO₂ nanosheets synthesized via hydrothermal methods are cutting-edge materials with great potential for photocatalytic H₂ evolution.¹ Despite its potential, the wide optical bandgap and low catalytic activity of TiO₂ impede its performance.² Numerous studies have aimed to address these challenges, significantly enhancing its photocatalytic properties.³ In this work, we present an approach to further improve the photocatalytic H₂ production activity of anatase TiO₂ nanosheets by incorporating vanadium as a co-catalyst on the surface of TiO_2. The modified TiO₂ nanosheets were characterized by transmission electron microscopy, ToF-SIMS, and photoelectrochemical hydrogen evolution.

In the present study, we describe modifying the TiO₂ nanosheets by loading vanadium as a co-catalyst using a high-power sonochemical treatment to enhance the photocatalytic hydrogen reaction rates. The results of this study offer a novel approach to improve the efficiency of anatase TiO₂ nanosheets for photocatalytic H₂ evolution, with potential applications in renewable energy conversion and storage.

Keywords: Anatase TiO₂, photocatalytic H₂ evolution, co-catalyst, ToF-SIMS

References

[1] Hejazi, S., Mohajernia, S., Osuagwu, B., Zoppellaro, G., Andryskova, P., Tomanec, O., Kment, S., Zbořil, R., & Schmuki, P. (2020). On the Controlled Loading of Single Platinum Atoms as a Co-Catalyst on TiO₂ Anatase for Optimized Photocatalytic H₂ Generation. Advanced Materials, 32(16). https://doi.org/10.1002/adma.201908505

[2] Lee, K., Mazare, A., & Schmuki, P. (2014). One-dimensional titanium dioxide nanomaterials: nanotubes. Chemical Reviews, 114(19), 9385–9454. https://doi.org/10.1021/CR500061M

[3] Hejazi, S., Killian, M.S., Mazare, A., Mohajernia, S. (2022). Single-Atom-Based Catalysts for Photocatalytic Water Splitting on TiO₂ Nanostructures. Catalysts, 12, 905, https//doi.org/10.3390/catal12080905.

To realise their full functionality, many bacterial cells rely on the incorporation of metals on various levels of their cellular structure, which are associated with a wide variety of functions, ranging from S-layer formation and stability to cellular navigation. We use a combination of cryogenic scanning electron microscopy (SEM) and focused on beam (FIB) imaging with chemical analysis by time of flight secondary ion mass spectrometry (ToF-SIMS) to study the role of metals as well as small molecules in the context of bacterial cells, focusing on the examples of Caulobacter crescentus, whose S-layer stability crucially depends on the presence of calcium ions, and Magnetospirillium magneticum, which uses magnetosomes, membranous structures containing magnetite crystals, for orientation in the Earth’s magnetic field. As many cellular processes, for example regarding the cell’s life cycle, are associated with the presence of specific metal and small molecule ions, simultaneous spatial and chemical imaging in frozen cellular samples can provide insights into these mechanisms.

Digitally printed electronics are a driver for novel research in various fields owing to their design flexibility and other advantages such as expedited time-to-market. Ink-jetting of nano colloidal materials (also known as 0D materials), such as metal nanoparticles, semiconductor quantum dots, intrinsically conductive polymer colloids and graphene flakes have been successfully employed in applications ranging from wearable electronics to quantum optoelectronic devices and fully printed perovskite solar cells. However, the performance of printed devices can be lower than those made by traditional manufacturing methods and is not fully understood. Here we report on how SIMS is helping to understand inkjet-printed 0D materials and informing the development of novel formulations with enhanced performance.

We report that anisotropic electrical conductivity of printed silver nanoparticles (AgNPs) is caused by organic residues from their inks [1]. We used ToF-SIMS in combination with X-ray photoelectron spectroscopy (XPS) to show that the polymer stabiliser polyvinylpyrrolidone tends to concentrate between vertically stacked nanoparticle layers as well as at dielectric/conductive interfaces. Furthermore, highly mobile Ag ions generated in the presence of heat and applied electric fields are capable of diffusion, which has detrimental effect on the quality of the gate in Si/SiO₂-based devices. We have recently developed a gold NPs (AuNPs) conductive ink with the potential to overcome these limitations [2]. We employed a multifunctional thiol (TrisSH) in the ink to prevent the formation of microcracks and pores by mediating the cohesion of AuNPs via interaction between the thiol groups and the gold surface, which results in more uniform printed structures. The role of TrisSH as a cohesion enhancer is confirmed by OrbiSIMS and XPS.

All-inorganic perovskite nanocrystals (NCs) with enhanced environmental stability are of interest for optoelectronic applications. We report on the formulation of CsPbX3 (X is Br or I) inks for inkjet deposition and utilise these as photosensitive layers in graphene photodetectors [3]. We achieve a high photoresponsivity in the visible wavelength range and a spectral response controlled by the halide content of the perovskite. By utilising perovskite NCs, iGr and AuNPs, we fully inkjet-printed a photodetector with high performance explained by transfer of photo-generated charge carriers from the NCs into graphene and charge transport through the iGr network. ToF-SIMS Depth profiling revealed the presence of perovskites throughout the iGr layer.

The approaches developed here can be adopted for other 0D materials and enable in depth understanding of printed layers and interfaces, needed to unleash the potential of inkjet printing for fabrication of electronics and optoelectronics.

[1] G. F. Trindade et al., “Residual polymer stabiliser causes anisotropic electrical conductivity during inkjet printing of metal nanoparticles,” Commun. Mater., vol. 2, no. 1, pp. 1–10, 2021, doi: 10.1038/s43246-021-00151-0.

[2] J. Im et al., “Functionalized Gold Nanoparticles with a Cohesion Enhancer for Robust Flexible Electrodes,” ACS Appl. Nano Mater., vol. 5, no. 5, pp. 6708–6716, 2022, doi: 10.1021/acsanm.2c00742.

[3] J. S. Austin et al., “Photosensitisation of inkjet printed graphene with stable all-inorganic perovskite nanocrystals,” Nanoscale, vol. 15, no. 5, pp. 2134–2142, 2022, doi: 10.1039/d2nr06429d.