A surface-enhanced Raman scattering (SERS) technique was used to obtain the information about the characteristics of conformation and surface property of isoleucine self-assembled monolayers (SAM). SERS spectra of isoleucine SAM modified at electrochemically roughened silver surface were obtained when solution pH value or electrode potential was changed. The results reveal that isoleucine molecules were adsorbed mainly via the deprotonated carboxyl groups at the roughened silver electrode. This feature was not changed significantly with variation of the solution pH value. The surface acid-base property of the SAM was also analyzed and characterized by means of an SERS titration method. Perchlorate ion was used as a spectroscopic probe in the SERS titration. As for the influence of the electrode potential on the SAM, it is revealed that the isoleucine molecules were adsorbed via the deprotonated carboxyl groups and amino groups within the range of electrode potential in this research. Adsorption of these isoleucine molecules on Ag surface was changed obviously with the shift of electrode potential along the negative direction.

Key words: isoleucine, self-assembled monolayer, surface-enhanced Raman spectroscopy, pH value, electrode potential