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

Abstract

Surface-enhanced Raman scattering (SERS) enhancement factors (EF) were evaluated for RNA mononucleotides: adenosine 5'-monophosphate (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_Cl nsp (EF ≈ 104), for AMP only on the citrate coated silver nanospheres, Ag_cit nsp (EF ≈ 103), 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 purine mononucleotides, AMP and GMP, more strongly scattered radiation on Ag_Cl nsp, and the pyrimidine mononucleotides, 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 × 106), than for CMP and UMP (EF ≈ 5 × 104).