SURFACE-ENHANCED RAMAN-SPECTROSCOPY OF NUCLEIC-ACID COMPOUNDS AND THEIR MIXTURES

Surface-Enhanced Raman Spectroscopy (SERS) has been used to characterize nucleic acid compounds - such as free bases, mononucleotides, and dinucleotides-to study the viability of the technique to analyze mixtures of the various compounds and to see whether the SERS properties of the dinucleotides are sequence dependent. To these ends, silver colloids (sols) prepared by citrate reduction methods have been used as the enhancing surface. We have found that some components show stronger enhancement than others and that the more strongly enhanced species tend to dominate spectra of equimolar mixtures. In addition, the relative intensities of the spectra of mixtures are different from the spectra of the individual components added together. This is likely due to competition among the analyte molecules for enhancing surface sites and to the surface potential of the enhancing agent favoring certain components over others. Despite these occurrences, the spectral features of various compounds are additive, and the spectrum of one component can be subtracted from the spectrum of the mixture with the features of the others left intact. Also, the enhancement of the various components is pH dependent, and is different from an aqueous medium to an electrophoresis gel medium. SERS shows considerable promise as a tool for characterizing mixtures of nucleic acid compounds.