SURFACE-ENHANCED NEAR-INFRARED RAMAN-SPECTROSCOPY OF NICOTINAMIDE ADENINE DINUCLEOTIDES ON A GOLD ELECTRODE

Near-infrared Fourier transform Raman spectroscopy was used to study t he surface-enhanced Raman spectroscopy (SERS) behavior of nicotinamide adenine dinucleotide (NAD) on a gold electrode. It was found that the quality of SERS can be largely improved by using a near-infrared lase r as the exciting source. Many bands, which cannot be enhanced in conv entional SERS excited by visible light, can be observed clearly in FT- SERS. The potential, pH, and concentration dependence of the SERS reve aled that NAD adsorbed on a gold electrode can be opened to a certain extent. Either the adenine or the nicotinamide moiety may change their adsorption states during the potential scanning process. The FT-SERS of NAD exhibits quite different properties from conventional SERS in t wo aspects: (1) the spectrum is quite dependent on applied voltages no t only in peak intensities, but also in band positions; in visible exc ited SERS, NAD and its analogues showed no potential dependence or onl y manifested changes in peak intensities; (2) a small peak coupled wit h the ring breathing vibration band of the nicotinamide moiety appeare d and increased with a negative shift of the potential. In contrast, o nly a single peak for this mode appeared in visible excited SERS. In a ddition, a very interesting phenomenon was observed in that a group of new bands appeared in the positive potential region which are similar to those with NAD binding a dehydrogenase enzyme. These results imply strongly that a charged and roughened electrode may be useful as an a rtificial enzyme model. (C) 1997 Elsevier Science S.A.