SERS and DFT investigation on the adsorption of 1,10-phenanthroline on transition metal surfaces.

SERS spectra of 1,10-phenanthroline (phen) on iron smooth surface doped with silver nanoparticles have been recorded and compared with those previously obtained on Ag doped smooth silver, copper and nickel surfaces. In order to correctly assign the SERS spectra, DFT/B3LYP calculations of phen and different models of phen/metal surface complexes have been performed. The 6-311++G(d,p) basis set was used for phen, whereas a mixed basis 6-311++G(d,p)/LANL2DZ was utilized in the case of the phen/metal complexes. From the comparison between the experimental and computational data, it was evidenced that phen was chemisorbed through its N atoms to the Ag, Cu, Ni and Fe surfaces, whereas the deposited Ag colloidal nanoparticles only played the role of providing the electromagnetic enhancement (with a factor of more than 10(3)) necessary to detect a suitable SERS signal.

Stable and efficient silver substrates for SERS spectroscopy.

Silver substrates have been obtained, by depositing silver colloidal nanoparticles on a roughened silver plate treated with 1,10-phenanthroline, and checked by means of AFM microscopy and Raman spectroscopy. The ligand molecules are located between two silver substrates and undergo the SERS (Surface Enhanced Raman Scattering) enhancement of both the roughened silver plate and the silver colloidal layer deposited on it. These SERS-active substrates, which show the advantages of being stable with respect to the metal colloidal suspensions, along with an easy and reproducible preparation, can be very useful for catalytic and analytical applications of the SERS spectroscopy.

Surface-enhanced Raman scattering investigation of the adsorption of 2-mercaptobenzoxazole on smooth copper surfaces doped with silver colloidal nanoparticles.

The adsorption of 2-mercaptobenzoxazole on copper has been investigated by means of surface-enhanced Raman scattering (SERS) by doping smooth copper surfaces with silver colloidal nanoparticles. The metal surfaces have been characterized by means of atomic force microscopy measurements. The compound adsorbs on the Cu/Ag surfaces in its ionized thiolic form, adopting a tilted orientation with respect to the metal surface. The anion is chemisorbed through the sulfur and nitrogen atoms on the smooth copper surface, and the silver colloidal nanoparticles only enhance the Raman signal due to the electromagnetic mechanism. SERS data have been interpreted with the help of DFT calculations on models of the ligand bound to copper adclusters.

Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles.

The halide anion effect on the adsorption of 1,2,3-triazole on Ag and Au colloidal nanoparticles has been investigated by means of surface enhanced Raman scattering (SERS), UV-visible absorption spectroscopy, and scanning electron microscopy. To interpret the SERS spectra, the vibrational spectra of 1,2,3-triazole were assigned with the help of density functional theoretical (DFT) calculations of the two tautomers of 1,2,3-triazole, both free and bound to Ag and Au adatoms. Upon addition of halide anions, both tautomers interact with the Ag surface through one nitrogen atom. Analogous behavior is observed in the case of basified Au colloids, whereas at the usual pH of these hydrosols (approximately 6) the adsorption of 1,2,3-triazole is the same of that observed in halide-free colloids.

Gold/palladium and silver/palladium colloids as novel metallic substrates for surface-enhanced Raman scattering.

New surface-enhanced Raman scattering (SERS) substrates, composed of gold or silver colloidal nanoparticles doped with palladium, were prepared. These novel colloids are stable and maintain a satisfactory SERS efficiency, even after long aging. The interest in doping the coinage metal nanoparticles with palladium is due to the well-known catalytic activity of this metal. Transmission electron microscopy (TEM) and ultraviolet-visible absorption spectroscopy were used to characterize the shape and size of the metal particles. It was found that these bimetallic colloidal nanoparticles have a core-shell structure, with gold or silver coated with palladium clusters.

Surface-enhanced raman scattering investigations of 4-nitro(pyridine N-oxide) and 4,4'-azobis(pyridine N-oxide) adsorbed on silver colloidal nanoparticles.

A spectroscopic investigation on the adsorption process of 4-nitro(pyridine N-oxide) (NPO) onto silver colloidal nanoparticles has been performed by Raman and UV-visible absorption measurements. Discrepancies between the Raman spectra of NPO in aqueous solution and in Ag hydrosol prompted an extension of the SERS study to include an investigation on the reactivity of this compound in silver colloidal suspension. The data are diagnostic of a reduction of the nitrogroup of NPO with subsequent formation of 4,4'-azobis(pyridine N-oxide) (APO). Hence, the adsorption mechanism and the molecular arrangement of APO adsorbed on the silver surface have been investigated by means of the SERS technique with the help of Density Functional Theoretical calculations of models of APO bound to a silver surface adatom.

SERS studies of the adsorption of guanine derivatives on gold colloidal nanoparticles.

Surface enhanced Raman scattering spectra of guanine, guanosine and 2'-deoxyguanosine adsorbed on gold colloidal nanoparticles were obtained. From the striking similarity of the SERS spectra of these compounds, it can be evidenced that guanosine and 2'-deoxyguanosine adsorb on gold nanoparticles through the guanine moiety. The molecular sites involved in the interaction with the gold surface are the same for the 3 compounds: the oxygen of the carbonilic group and the N(7) atom. Guanine, guanosine and 2'-deoxyguanosine adsorb on the gold substrates with a tilted orientation with respect to the metal surface. SERS data were interpreted taking into account density functional theoretical (DFT) calculations of guanine.