Surface-enhanced Raman Scattering Enhancement Factors for RNA Mononucleotides on Silver Nanoparticles

Surface-enhanced Raman scattering (SERS) enhancement factors (EF) were evaluated for RNA mononucleotides: adenosine 5'-mono phosphate (AMP), guanosine 5'-monophosphate (GMP), cytidine 5'-monophosphate (CMP) and uridine 5'-monophosphate (UMP), on silver nanoparticles, which differed in shape (nanospheres, nanostars) and stabilizing anionic layer (chlorides, citrates) on the metal surface. In freshly prepared silver colloids the enhanced Raman scattering was observed for all the RNA mononucleotides on the chloride coated silver nanospheres, Ag_CI nsp (EF = 104), for AMP only on the citrate coated silver nanospheres, Ag_cit nsp (EF approximate to 10(3)), while not obtained at all for any of the mononucleotides on the citrate stabilized silver nanostars, Ag_cit nst. Upon aggregation, the SERS activity of all the silver colloids increased, whereby the punne mononucleotides, AMP and GMP, more strongly scattered radiation on Ag_CI nsp, and the pyrimidine mononucleondes, CMP and UMP, on Ag_cit nsp. Regardless of the silver nanoparticles, the higher EFs were evaluated for AMP and GMP (EF up to 5 x 10(6)), than for CMP and UMP (EF approximate to 5 x 10(4)).