Time Dependence of SERS Enhancement for Pyrimidine Nucleosides

The effects of chemical components in a SERS sample preparation on the time scale of the SERS enhancement process have not previously been examined in detail. In this report the effects of the nature and concentration of aggregating agent as well as the concentration of both colloid and analyte on the time dependence of SERS enhancement and on the spectral profiles observed for the pyrimidine nucleosides cytidine and uridine are characterized. In conjunction with hydrodynamic diameter and zeta-potential measurements the differences in SERS enhancement profile with time observed for the aggregating agents studied (KCl and K2SO4) are ascribed to two competing processes affecting the SERS substrate nanoparticles. The first being the conventional aggregation process and the second being an equilibrium between smaller and larger aggregates which is influenced by the presence of Cl- ions.