MOLECULAR RECOGNITION USING SURFACE-ENHANCED RAMAN-SCATTERING FROM CITRATE-REDUCED SILVER COLLOIDS IN NONAQUEOUS SOLVENTS

Surface-enhanced Raman scattering (SERS) from citrate-coated colloidal particles suspended in organic solvents is used to study surface reactions in an organic phase. Stable colloids which gave good SERS were produced from ethanol and acetonitrile. SERS was easily discriminated from the bulk solvent Raman scattering. Compounds which are sparingly soluble in water including 2,2'-bipyridine and benzene-1,2,4,5-tetracarboxylic acid dianhydride produced good SERS in ethanol. In the latter case, no SERS was observed from an aqueous colloid. Therefore, some form of solvent-dependent molecular recognition may operate. The formation of a bipyridine complex with copper(II) at the surface in a solvent system in which the ligand and complex are both soluble was observed. The solvent altered surface reactions. In the ethanol colloid, in contrast to the result in aqueous colloid, pyridine does not replace citrate readily. This work demonstrates the potential for the expansion of the use of colloidal SERS into the field of surface reactions in contact with an organic phase and is related to metal liquid-like films.