Surface-enhanced Raman of 1,5-dimethylcytosine adsorbed on a silver electrode and different metal colloids: Effect of charge transfer mechanism

The surface-enhanced Raman of 1,5-dimethylcytosine is analyzed on a metalli c electrode and colloids. The obtained results reveal the existence of a ch emisorption of DMC on both electrode and colloids. As a consequence, a sign ificant contribution from the charge transfer (CT) mechanism is expected. O n metal electrodes the variation of the potential induces a change of the s pectral profile that can serve to evaluate the charge transfer taking place between the metal and the adsorbate. The surface-enhanced Raman scattering (SERS) spectra of DMC on the silver electrode were compared with those rec orded on silver, gold, and copper colloids in order to obtain information a bout the electric potential existing in the colloidal surfaces as well as t o estimate the importance of the charge transfer occurring in these substra tes. On these metals the interaction strength tvas found to grow in the ord er Ag < Au < Cu, and this is related to the different energy necessary for inducing a charge transfer process between the metal and the adsorbate. Alt hough the CT mechanism only has a weak contribution to the total SERS enhan cement, in comparison to the electromagnetic, it may modify the SERS spectr um of a certain adsorbate, depending on parameters such as the surface morp hology, the presence of Cl-, or the metal employed for obtaining the SERS s ubstrate.