Quantitative assessment of surface-enhanced resonance Raman scattering forthe analysis of dyes on colloidal silver

Factors that affect quantitative analysis by surface-enhanced resonance Ram an scattering (SERRS) have been investigated using azobenzotriazol and reac tive dyes. Preaggregation of the silver colloid was the most effective meth od to obtain repeatable and reproducible scattering. Aggregation by poly(L- lysine) or spermine provided better precision than aggregation by sodium ch loride or nitric acid. Repeatable quantitative analysis was achieved with t he azobenzotriazol dyes. A linear calibration graph was obtained over diffe rent concentration ranges below 10(-8) M, depending on the nature of the co lloid. Calculations estimate that 10(-8) M is the concentration at which mo nolayer coverage of the dye on the silver colloid is achieved. Above 10(-8) M, there was only a minor increase in the scattering intensity from the az obenzotriazol dyes. In contrast, the reactive dyes did not give a response proportional to concentration over the range studied. The different respons es obtained for the two types of dye are believed to be caused by differenc es in the nature of the interaction of the molecules with the silver surfac e. The conclusion reached is that control of the colloid preparation, aggre gation process, and surface chemistry are essential for successful quantita tive analysis of dyes on colloidal silver by SERRS.