Chemisorption of cysteamine on silver studied by surface-enhanced Raman scattering

The chemisorption of cysteamine (2-aminoethanethiol) on silver, giving mono layers often used for adsorption of proteins, was studied using surface-enh anced Raman scattering (SERS). Raman measurements revealed that the ratio o f gauche-trans conformers of adsorbed cysteamine molecules significantly ch anged during the incubation. Layers with a higher ratio of trans conformers are formed when the time of incubation is relatively short (less than 1 h) . Long incubation leads to reconstructed layers with a higher portion of cy steamine molecules in gauche conformation. The results of SERS experiments reveal that cysteamine molecules during chemisorption do not replace the la rge part of preadsorbed Cl- anions and that the structure of the obtained m onolayer strongly depends on the surface concentration of preadsorbed chlor ides. The effect of prolonged treatment of cysteamine layers by various ele ctrolytes was also investigated. Raman spectroscopy revealed that after the transfer of the monolayer of cysteamine on silver to the solution containi ng ClO4- or SO42- anions, a relatively large amount of these anions is coad sorbed. However, after about 1 day, the bands of ClO4- and SO42- anions dis appear, whereas the spectrum of adsorbed cysteamine is still well visible. Possible explanations for these experimental findings are discussed. Our re sults provide some suggestions that may help to obtain more uniform monolay ers, terminated by amino groups, which are desired for various applications .