Surface-enhanced Raman spectroscopy of peptides and proteins adsorbed on an electrochemically prepared silver surface

Abstract

Surface-enhanced Raman (SER) spectra of a range of small peptides and proteins were obtained from an electrochemically roughened silver surface using a Raman microprobe spectrometer, and from analysis of these spectra the orientations of these molecules on the silver were elucidated. From the spectra it was proposed that all of the di- and tripeptides were adsorbed onto the silver through the carboxyl terminus, and that dominant peaks were due to the side chains of the amino acid residue closest to the carboxyl terminus, regardless of the SER scattering (SERS) activity of individual amino acid residues. SER spectra of the polypeptides and proteins were dominated by amide bands and aromatic side chain vibrations. For most samples, the SER spectrum could be related to the secondary structure of the protein on the silver surface.