High sensitivity Surface Enhanced Raman Scattering Detection of Organic Molecules and Amino Acids

Surface enhanced Raman scattering is a promising technique for high sensitivity analytical applications. However, there are issues which have to be addressed in order to make SERS a reliable technique such as the optimization of conditions for any given analyte, understanding the kinetic processes of binding of the target molecules to the nanostructures and understanding the evolution and coagulation of the nanostructures, in the case of colloidal solutions. The background electrolyte is a very important factor in SERS experiments. Here we report a detailed study of the influence of the addition of different types of electrolytes on the amplitude and kinetics of the SERS signal in silver colloids. Different amino acids and organic dyes were used as test molecules in the concentration range of 10(-8) to 10(-4) M. We found that a new proposed electrolyte containing HCO3, CO3, Cl and SO4 ions provides very high enhancement of Raman signal in organic molecules we studied. The advantages of the composite electrolyte are especially noticeable at low concentration of tryptophan where we observed 10(8) enhancement of Raman signal, approximately 300 times larger than for the case of commonly used electrolyte sodium chloride.