SHINERS e SHINEF: uma nova proposta de intensificação do sinal Raman e fluorescência

Abstract

The studies to aimed the interface metal/molecule resulted in the discovery of the SERS effect. The SERS effect was discovered accidentally and can increase the intensity of scattering adsorbed species ca. 106 times. The SERS performance depends on several parameters such as: size, shape and nature of the metallic nanostructures. To avoid aggregation and deposition of nanoparticles, a new methodology is proposed in this dissertation: coat the NPs with inert materials like SiO2 and MnO2. The cited methodology receives the name of SHINERS. Another technique that has been receiving great notoriety due to applications in biological systems is the SEF effect. A specific spacing between the fluorophore and NP is necessary for the SEF effect to occur and it can be accomplished by coating with inert oxides, which takes the denomination of SHINEF. The distance from the surface causes a decay of the signal, therefore, the layers are supposed to be ultrathin with precise thickness control for optimized results. In order to obtain a good SHINERS and SHINEF performance, in this dissertation, Ag and AuNPs coated with ultrafine layers of SiO2 and MnO2 to different thicknesses were prepared. It had been possible to characterize the coating of metal oxide NPs by using TEM. It has been determined covering oxide layer thickness of 2-6 nm. The coating of NPs causes a shift of LSPR bands for higher wavelength of the coating nanoparticles compared to uncoated NPs, assigned to increasing changes in the local refractive index of the NPs with the oxide layer thickness. The resulting nanomaterials performances for SHINERS and SEF effect were studied using IR-820 dye, which had its vibrational spectrum assigned. There has been observed a decrease in the SHINERS intensity with the increasing thickness of the coating in relation to the SERS intensity attributed to the increasing distance of the adsorbate from the NPs surface. For SHINEF effect, it has been found that a significant enhancement of fluorescence emission occurs when IR- 820 dye in the presence of the coated NPs excited at 785 nm. The preparative methodologies proposed in this dissertation are promising for the application of coated Ag and Au NPs as substrates for high performance SHINERS and SHINEF techniques.