Síntese e caracterização microestrutural de nanopartículas de ouro

Abstract

This work presents the results of the microstructural and optical characterization of gold nanoparticles (AuNPs) at room temperature, synthesized by the colloidal method described by Turkevich and Frens. The evolution of the microstructural parameters, as a function of the synthesis variables, were investigated by X-ray Profile Analysis (XPA) and Transmission Electron Microscopy (TEM) techniques. The reduction of the AuNPs was verified through the qualitative analysis of the X-ray diffractograms as a function of the increase of the Sodium Citrate solution. This behavior was confirmed by the fitting of the diffraction profiles through the Convolutional Multiple Whole Profile fitting method (CMWP-fit), using parameters of crystalline sizes contributions and instrumental influence on the measurements. TEM measurements observed AuNPs with approximately spherical symmetry were obtained, where the agglomeration process was visualized through the fusion of two or more smaller particles. This result could explain the difference of the microstructural parameters obtained by X-ray diffraction as microscopy. For the study of optical properties, Phantoms were synthesized by adding AuNPs in a matrix composed of gelatin and chitosan to simulate the behavior of biological tissues. The absorbance spectra for these Phantoms were compared to those obtained for the colloidal solutions, where the optical behavior of the AuNPs is quite sensitive to their size and variation of the medium, with the shift of absorption maximum and breadth of the spectrum. This result is of great importance for the construction of biological markers, enabling the accompaniment of cellular activities directly by altering the wavelength absorbed as a function of the chemical alteration of the medium.