SERS study of methylated and nonmethylated ribonucleosides and the effect of aggregating agents

We present surface-enhanced Raman scattering (SERS) spectra of the RNA nucleosides adenosine, cytidine, guanosine and uracil and the methylated derivatives 5-methylcytidine and 7-methylguanosine, a class of important nucleic acid components that has not previously been well characterised using SERS spectroscopy. Our work shows that the selection of aggregating agent plays a crucial role for SERS analysis of these nucleosides with K2SO4 generating immediate enhancement while NaCl only gave immediate enhancement for the pyrimidine nucleosides. The SERS spectra contain a number of marker bands that are highly sensitive to structural differences between these nucleosides, in particular methylation, and at lower concentration ranges than are possible for conventional Raman scattering. Finally, spectral analyses and assignments of the vibrational modes responsible for these marker bands are also presented, and the effect of the aggregating agent on these modes is discussed in terms of interactions between each nucleoside and the metal surface. Copyright (C) 2011 John Wiley & Sons, Ltd.