Surface-Enhanced Raman Scattering (SERS) Study of Mercaptoethanol Monolayer Assemblies on Silver Citrate Hydrosol. Preparation and Characterization of Modified Hydrosol as a SERS-Active Substrate

The self-assembling technique was employed for modification of a citrate-reduced silver hydrosol with mercaptoethanol (ME). The results of investigation of the structure and properties of both the self-assembled monolayers (SAMs) of ME and the modified hydrosol as a substrate for surface-enhanced Raman scattering (SERS) spectroscopy are presented. ME chemisorbs on the hydrosol by rupture of the S−H bond with concomitant bonding of the sulfur headgroup to Ag. Chemisorption is accompanied by gauche−trans isomerization of ME. The isomerization occurs cooperatively at submonolayer coverage due to interactions of neighboring adsorbed molecules rather than due to the chemisorption itself. The chemisorption of ME takes place on a less than 5 min time scale and leads to formation of a SAM with definite density and gauche−trans equilibrium, the parameters of which depend on the bulk concentration of ME but not on the time of incubation. It was revealed that densely packed and highly ordered (97% of trans-isomers) ...