Highly reproducible SERS detection in sequential injection analysis: Real time preparation and application of photo-reduced silver substrate in a moving flow-cell

This paper reports an improved way for performing highly reproducible surface enhanced Raman scattering of different analytes using an automated flow system. The method uses a confocal Raman microscope to prepare SERS active silver spots on the window of a flow cell by photo-reduction of silver nitrate in the presence of citrate. Placement of the flow cell on an automated x and y stages of the Raman microscope allows to prepare a fresh spot for every new measurement. This procedure thus efficiently avoids any carry over effects which might result from adsorption of the analyte on the SERS active material and enables highly reproducible SERS measurements. For reproducible liquid handling the used sequential injection analysis system as well as the Raman microscope was operated by the flexible LabVIEW based software ATLAS developed in our group. Quantitative aspects were investigated using Cu(PAR)2 as a model analyte. Concentration down to 5×10−6 M provided clear SERS spectra, a linear concentration dependence of the SERS intensities at 1333 cm−1 was obtained from 5×10−5 to 1×10−3 with a correlation coefficient r=0.999. The coefficient of variation of the method Vxo was found to be 5.6% and the calculated limit of detection 1.7×10−5 M. The results demonstrate the potential of SERS spectroscopy to be used as a molecular specific detector in aqueous flow systems.