Surface enhanced Raman spectroscopy as a molecular specific detection system in aqueous flow-through systems

Abstract

Surface enhanced Raman scattering (SERS) is proposed as a molecular specific technique for direct measurements of organic molecules in aqueous solutions. An FT-Raman spectrometer was interfaced with a flow injection manifold operated in the stopped flow mode enabling reproducible collection of SERS spectra due to the automation of the analysis procedure. For SERS a solid state substrate placed in a newly developed flow-cell was used. Multiple measurements on one single SERS substrate were achieved by rinsing the substrate with reagents such as 3 M KCl or 0.1 M NaOH solutions prior to the next measurements in order to remove retained analytes from the surface of the SERS substrate. This procedure allowed for improved precision as compared with a conventional batch approach. Quantitative aspects were investigated by establishing a calibration curve for nicotinic acid which was used as a model analyte. A linear dependance of the recorded SERS intensities from the logarithm of the analyte concentration was obtained throughout the whole investigated concentration range (0.001–0.1 M, correlation coefficient r² = 0.97). The standard deviation of the method s_x0 was found to be 0.122 mM and detection limit 1.7 mM, respectively. The results demonstrate the potential of SERS spectroscopy to be used as a molecular specific detector in aqueous flow systems such as flow injection analysis.

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