Estudo da interação de biomoléculas com superfícies metálicas por espectroscopia SERS

Abstract

In this dissertation the Surface Enhanced Raman Scattering (SERS) spectroscopy was used to monitor molecules with biological interest adsorbed on gold or copper metallic surfaces. Different gold metallic nanoparticles were synthesized varing the concentration, the addition order of the reagents and the temperature in which the syntheses were made. The size distributions were estimated for each colloid synthesis by the extinction spectra of the suspensions, and the samples were also analyzed by scanning electronic microscopy and dynamic light scattering techniques. Copper nanoparticles were obtained in aqueous media, undergoing surface oxidation with the formation of Cu(II) oxide, whose kinetic was followed by extinction spectra. When a reducer adsorbate was added to the nanoparticle suspension, the copper oxide, present in the metallic surfaces, undergoing reduction, allowing the achievement of SERS spectrum of the adsorbate in the oxidized form. The molecule which allowed the study of this redox mechanism was p-phenylenediamine, and the SERS spectrum was obtained from the radical cation species. Serotonin, adrenaline, L-carnosine, melatonin, rifampicin and bovine serum albumin were the adsorbates selected to obtain the SERS spectra in gold colloids. These molecules exhibit aromatic rings, whose is expected high contribution for the molecular polarizability, and in consequence of this a great SERS signal. Such species also have nitrogen and oxygen atoms, which are available coordination sites for interaction with the metallic surface. Different exciting radiations were used for searching of the resonance with the localized surface plasmon transitions of the gold nanoparticles. It was made the vibrational theoretical calculations for each studied adsorbate, isolated and coordinated to one or more gold or copper atoms, that were used for the assignment of Raman and SERS spectra of the solid and the surface complex, respectively. Through such assignment and the surface selection rules it was possible to determinate the adsorption geometry of biomolecule on the metallic surface.