SURFACE-ENHANCED RESONANCE RAMAN-SCATTERING

Surface-enhanced resonance Raman scattering (SERRS) is a sensitive and selective method for the characterization of sites in biomolecules, which have an electronic transition at energy close to or coincident with the laser frequency used. The biomolecule is adsorbed on a suitable metal substrate, normally silver, and the measurements are usually taken in situ in buffer or support medium. The method has specific advantages. It is possible to combine the sensitivity of resonance with the sensitivity of surface-enhanced Raman scattering (SERS) so that very low concentrations can be used. In some cases, there is greater discrimination against fluorescence than with resonance Raman scattering because of either energy transfer from the adsorbed protein to the metal substrate or discrimination against fluorescing impurities in the adsorption process. The SERRS technique is selective, combining the distance and orientation selection rules of SERS with the selectivity implicit in thc resonance effect. The main disadvantages of SERRS are that (1) the nature of the metal is critical, and silver, a rather reactive metal, is the ideal, although not the only, choice, (2) the theory is only partially understood, and consequently the full interpretation of the data is difficult, and (3) adsorbed rather than free protein is sampled. The method is essentially a development of resonance Raman scattering and SERS, and its application in biological systems has been discussed. The way in which the theory of the technique has developed is dependent on a basic understanding of both resonance and SERS theory. © 1993, Academic Press, Inc.