Ag- and Cu-based Quantum Dots as Amplifiers for Surface-Enhanced Infrared Absorption Spectroscopy
Goreti Pereira1, Patrick Krebs2, Boris Mizaikoff2, Giovannia A.L. Pereira3, Claudete F. Pereira3
1Department of Chemistry and CESAM, University of Aveiro, Portugal; 2Institute of Analytical and Bioanalytical Chemistry, Ulm University, Germany; 3Department of Fundamental Chemistry, Federal University of Pernambuco, Brazil
Water contamination poses serious ecological and public health threats, potentially leading to potable water shortages worldwide. The widespread presence of organic microcontaminants in water resources has become a major international concern, prompting the European Union (EU) to establish a Water Watch List for monitoring these substances. Nowadays, the detection and quantification of these pollutants rely mainly on liquid or gas chromatography coupled with mass spectrometry (LC/GC–MS). Although these methodologies are precise and accurate, they require expensive equipment, experienced technicians, and are not suitable for field analysis or large and fast environment screenings. Therefore, there is a critical need for user-friendly, practical, and portable tools to enable in situ measurements for environmental monitoring.
Surface-enhanced infrared absorption (SEIRA) spectroscopy has great potential for the sensitive and portable detection of microcontaminants. Infrared (IR) spectroscopy is widely used for molecular identification, as it provides detailed information on the vibrational signature of chemical bonds. However, its effectiveness can be limited when dealing with compounds that exhibit weak IR absorption signals or even occur at low concentrations, making the detection of trace amounts of several contaminants difficult. To overcome this limitation, nanomaterials have been explored as amplifiers for SEIRA, allowing the detection of molecules at much lower concentrations.
Cu- and Ag-based quantum dots (QDs) have recently evidenced good optical properties, offering a key advantage of being toxic metal-free. In our group, we successfully optimized the aqueous synthesis of these QDs and demonstrated their potential for SEIRA analysis of organic microcontaminants in water. The use of Ag2Se and Cu2-xSe QDs to enhance infrared signatures of organic dyes revealed promising SEIRA results. Our results showed an enhancement factor of 1.8 – 10.9 for Ag2Se and 1.6 – 9.1 for Cu2-xSe, for several organic dyes. Furthermore, Ag2Se QDs were also able to detect the atrazine pesticide in concentrations as low as 0.001 μg/mL. These findings underscore the potential of Ag- and Cu-based QDs as effective nanoplatforms to improve the sensitive detection of organic microcontaminants in environmental monitoring.
Acknowledgements: The authors acknowledge financial support to CNPq, FACEPE, INCTAA, UID Centro de Estudos do Ambiente e Mar (CESAM) + LA/P/0094/2020, and the project NanoSEIRA (COMPETE2030-FEDER-00866600).
Mid-infrared laser-based air quality analyzers in mining scenarios
Lisa Walter1, Renan Kobal de Oliveira Alves Cardoso1, Fahd Al-Seba'ey1, Diandra Nunes Barreto2, Danielle da Silva Sousa3, David Gachet4, Jérémy Butet4, Richard Maulini4, Kaspar Suter4, Stéphane Blaser4, Boris Mizaikoff1,5
1Institute of Analytical and Bioanalytical Chemistry, Ulm University, Germany; 2Federal University of Sao Carlos, Brazil; 3Federal University of Uberlândia, Brazil; 4Alpes Lasers, Switzerland; 5Hahn-Schickard-Gesellschaft für angewandte Forschung e.V., Ulm, Germany
Exposure to toxic gases in underground workplaces, such as mines, presents serious risks to worker health and operational safety. Continuous monitoring of air quality—defined by the concentrations of toxic or hazardous gases including CO, CO₂, CH₄, NO, NO₂, SO₂, H₂S, and O₂—is essential to enable rapid hazard mitigation. This requires the capability to detect gas concentrations at trace levels and near real-time.
We present the development of a portable sensing system based on mid-infrared (MIR) absorption spectroscopy, employing quantum cascade lasers (QCLs)—designed and fabricated by Alpes Lasers—as tunable light sources, and substrate-integrated hollow waveguides (iHWGs) to enable robust, compact optical paths optimized for field deployment. The use of laser-based MIR spectroscopy allows for highly selective gas detection over broad concentration ranges, including high concentrations that may saturate or degrade conventional sensors.
The system is designed with special focus on high sensitivity, compactness, and robustness under harsh environmental conditions, including high humidity, dust, mechanical vibrations, and electromagnetic interference. Initial tests showed that gas measurements were not affected by strong vibrational disturbances, such as those caused by nearby rail traffic. In addition, exposure to high humidity conditions was tested without observable degradation in performance.
A user-friendly software interface supports visualization of concentration values and communication with a middleware layer, enabling automated safety alerts when gas concentrations exceed predefined thresholds.
This work is supported by the EU HORIZON 2022 project NETHELIX (No. 101092365).
Keywords: environmental analysis, gas analysis, harsh conditions, mid-infrared, quantum-cascade laser, substrate-integrated hollow waveguide
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