Adsorption of seleno-L-cystine on a silver electrode surface was examined by means of surface-enhanced Raman scattering (SERS). The seleno-L-cystine appeared to be adsorbed on Ag surfaces mainly via the strong Ag-Se bonding that developed after the Se-Se breakage. On an Ag electrode with negative potentials greater than ca. 0.2 V, the co-adsorbed chloride ions appeared to leave the surface as the potential was swept toward the negative values. Spectral frequency shifts of the CH2 and CSe stretching bands supported a potential-induced adsorption change in the selenocysteine on a silver electrode depending on the applied voltage. (c) 2007 Elsevier B.V. All rights reserved.