A spatial distribution study of analyte concentration in solid substrate surface-enhanced Raman spectroscopy

As surface-enhanced Raman spectroscopy becomes more widely used as a technique for routine analysis, attention must be given to factors which affect the reproducibility of the technique. One such factor which has not been considered is the effect of the spatial distribution of molecules in an analyte spot on a solid SERS substrate. In this study, we demonstrate that the spatial distribution of analyte can be quite non-uniform due to chromatographic interactions between the analyte molecules, solvent and support used. The SERS signal obtained is highly dependent on the position of the laser beam in the analyte spot. The SERS signal is also dependent on the relative sizes of the analyte spot and the laser beam at the sample. This latter dependence can not be explained with current theoretical treatments. However, we demonstrate that a simple modification of the current theory can qualitatively explain the results we observe.