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New chemical sensors by combining IR absorption and reflectometric interference spectroscopy

Final Activity Report Summary - IRRIS (New chemical sensors by combining IR absorption and reflectometric interference spectroscopy)

The main objective of this project was the development of sensing methods for gas and solution analytes using optical spectroscopic methods. For analytes in gas phase a new sensing approach was developed by combining infrared (IR) absorption spectroscopy and reflectometric interference spectroscopy (RIfS). This sensing approach was advantageous because the IR spectra recorded in reflectance on approximately 3 µm hydrophobic polymer layers, spin-coated on silicon (Si) or germanium (Ge) plates, comprised both molecular IR absorption bands and the interference pattern generated by the polymer film. The polymer layer was exposed to gas analyte, thus enrichment in the polymer film occurred. The IR molecular specific part of the spectrum offered qualitative information concerning the analyte, whereas quantitative assessments could be obtained from both IR absorptions and shifts of the interference pattern, because of swelling of the polymer layer caused by gas permeation. Polyetherurethane, polydimethylsiloxane, Makrolon and polyisobuthylene polymer layers were tested for such IR-RIfS measurements, whereas toluene, o-dichlorobenzene, m-xylene, ethyl acetate, acetone and cyclohexane were successfully employed as analytes. Water vapour influenced neither the IR absorptions nor the interference pattern when hydrophobic polymers were used. Thus, this IR sensing scheme could be employed even under moistly conditions.

For analytes in solutions a new sensing method was developed by combining Raman spectroscopy with capillary electrophoresis (CE). To enhance the Raman signal a silver substrate was prepared in situ in the capillary column by laser induced growth of silver particles. For that purpose, silver nitrate was added to the 10 mM citrate buffer, up to a concentration of 0.5 mM. Accurate separations and intense surface-enhanced Raman spectra (SERS) were shown by CE-SERS three-dimensional electropherograms for the analytes rhodamine 6G, 4-(2-pyridylazo)resorcinol (PAR), PAR complex with Cu(II) and methylene blue at concentrations between 2 and 20 ppm, by using HeNe laser intensities in the range of 1.4 to 3.6 mW. The silver substrate was found to have no significant influence on the electrophoretic separation process, the analyte peaks represented in the UV electropherogram being clearly confirmed by the recorded SERS spectra.

CE played an essential role in the successful accomplishment of the human genome project, whose goal was the unravelling of the sequence of human deoxyribonucleic acid (DNA). Since the sequencing of the human genome, capillary electrophoresis techniques continued to improve and carry out new functions. Taking into account the importance of CE, the novel Raman detection for CE that was developed was expected to find applicability in the field of biosensing, as well as for food safety and security assessments, environmental monitoring etc.

For the determination of glucose, fructose and sucrose in apple juices, the work with chemometric methods was acquired by the fellow. Chemometric interpretation of the recorded spectra would be, for example, useful in quality and safety assessments of food products. Thus, fourteen apple juice samples were analysed. From the prediction results it could be observed that the deviation of the predicted values was below 10 % for most samples. This was a good proof that the developed partial least squares (PLS) model was correct, enabling accurate prediction. Most juices presented fructose, glucose and sucrose values in the expected typical range. However, several samples with deviations from standard values could be detected and interpreted in terms of juice quality.