Characterization of the [Ru(CN)5(pyS)] ion complex adsorbed on gold, silver and copper substrates by surface-enhanced Raman spectroscopy

The adsorption of the Ru(CN)₅(pyS)]⁴⁻ (pyS=4-mercaptopyridine) ion complex on gold, silver and copper surfaces has been studied by surface-enhanced Raman spectroscopy (SERS). The influence of the nature of the metallic substrates in the adsorption geometry of the complex is reflected in a strong variation of the SERS spectra, particularly, the relative intensities of characteristic vibrational modes of pyS and CN ligands, which is likely to result from changes in specific chemical interactions involving both ligands and the surface. The effect of the surface modification procedure on the properties of the adsorbed monolayers has also been investigated for the gold surface. Surface modification has been performed by self-assembly or under an electrochemical potential. The spectroscopic results have shown that, according to the modification procedure, the modifier can be bound to the surface via sulfur atom or via CN nitrogen atoms. The ability to control the orientation of the adsorbed monolayer permits control over the properties of the interface, as demonstrated by the study of the electrochemistry of cytochrome-c (cyt-c) on the differently prepared surfaces. A reversible electrochemical response of the metalloprotein is only observed on the self-assembly prepared surface, where CN moieties of the surface modifier are available to interact with the protein molecule.