Surface-enhanced Raman scattering study of riboflavin on borohydride-reduced silver colloids: Dependence of concentration, halide anions and pH values

The influences of concentration, halide anions and pH on the surface-enhanced Raman scattering (SERS) of riboflavin adsorbed on borohydride-reduced silver colloids were studied. The optimum concentration for the SERS of riboflavin is 10−6 mol/L while the SERS enhancement varies for different modes. The addition of 0.2 mol/L halide (NaCl, NaBr, and NaI) aqueous solutions, leads to a general decrease of the SERS intensity and a change of spectral profile of riboflavin excited at 514.5 nm. Riboflavin interacts with the silver surface possibly through the CO and N–H modes of the uracil ring. The SERS spectra of riboflavin were recorded in the 3.4–11.6 pH range. By analyzing several SERS marker bands, the protonated, deprotonated or the coexistence of both molecular species adsorbed on the colloidal silver particles was proved.

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► New adsorption geometries of riboflavin molecules on silver surface were verified.
► The optimum concentration for the SERS of riboflavin was found at 10−6 mol/L.
► The addition of 0.2 mol/L halide leads to the changes of SERS intensity and profile.
► The protonated and deprotonated molecular species of riboflavin adsorbed were proved.