Incorporação de nanopartículas de ouro sobre monocamada automontada de benzenoditiol

Abstract

The Self-Assembled Monolayer (SAM), which is formed by spontaneous adsorption of chemical species on a surface, when combined with gold nanoparticles (AuNPs) can be used to build electrochemical biosensors destinated to detect biomolecules. This work had the intention to develop a chemically modified electrode, which is a platform, that might be used to build an electrochemical biosensor. Thus, the SAM modification method was used immerging a polycrystalline gold electrode in 1,4-bezenedithiol (BDT) solution, to form the modified electrode Au/BDT. After this procedure, the Au/BDT was immersed in gold colloidal solution (AuNPs) for 2 hours, resulting on the Au/BDT/AuNPs electrode. So, correlating the vibrational SERS (Surface-Enhanced Raman Scattering) and Raman spectra, particularly related to the S–H bend and stretching modes, it was possible to infer the adsorption process of the BDT molecules onto gold occurs through one of the sulfur atoms. The monitoring of the formation of the BDT monolayer was performed by cyclic voltammetry and impedance in solution containing [Fe(CN)6]3-/4- ions as redox species. With the increase in the modification time, the voltammetric curves presented an increase in the peak potential difference (Ep) and the Nyquist diagrams obtained showed similar trend presenting an increase in the heterogeneous charge transfer resistance (RCT). Have proven that the sulfur atom was responsible to adsorb on gold, the modified electrode was used in a linear sweep voltammetry in alkaline medium to determine the desorption potential (-0.88 V vs Ag/AgCl) and the surface coverage (Γ = 1.62 x 10-10 mol cm-2). The AuNPs synthesized presented a band assigned to the surface plasmon resonance (SPR) with maximum at 534 nm being consistent with an average diameter of 56 nm. The addition of the AuNPs on the Au/BDT electrode was followed by cyclic voltammetry and impedance in solution containing [Fe(CN)6]3-/4- ions as redox species. The electrochemical and impedimetric results showed that the addition of the nanoparticles decreases the separation between the peak potentials as well as the heterogeneous charge transfer resistance on the interface Au/BDT/AuNPs with the redox species. In addition, the SERS spectra obtained for Au/BDT/AuNPs confirmed that the interaction of the nanoparticles with the SAM of BDT occurred through the terminal sulfur atom.