TOWARDS QUANTITATIVE SURFACE-ENHANCED RESONANCE RAMAN-SCATTERING (SERRS) - A STUDY OF AGGREGATION AND CONCENTRATION FOR 2 RHODAMINE DYES

A study of the effect of concentration of dye and of the conditions of aggregation for surface enhanced resonance Raman scattering (SERRS) f rom rhodamine 3B and 3G adsorbed on silver colloid indicates that quan titative results can be obtained provided that the concentration of th e dye on the colloid surface is kept well below monolayer coverage. Th ere are no interferences due to other adsorbates because of the predom inance of the scattering from the chromophore, In addition, fluorescen ce is quenched and low excitation powers are required, The signals are stable for at least 1 h and the RSDs are in the range 6-11% depending on the aggregation method, The preferred method of aggregation is to use as an aggregating agent poly(L-lysine) with ascorbic acid because poly(L-lysine) increases the control over the process. At concentratio ns equivalent to surface coverage above about one tenth of a monolayer , the dependence of signal on concentration is complex owing to change s in the packing and orientation of the dye at the surface and to mult i-layer effects, (C) 1998 John Wiley & Sons, Ltd.