Desenvolvimento de sensor eletroquímico fundamentado em monocamadas auto-organizadas de nanopartículas de ouro e 4-nitrotiofenol para detecção de ácido ascórbico

Abstract

The present work explores, for the first time, the electrocatalytic oxidation of AA using gold nanoparticles ECV electrode modified with in situ activated 4-nitrotiophenol (4-NTP) self-assembled monolayers (SAMs). The 4NTP-SAM was immobilized in a nanostructured platform containing a multi-walled carbon nanotubes (MWCNTs) and polyethyleneimine (PEI). The 4-NTP-SAM surface was characterized by thermal gravimetric analysis (TGA), scanning electron microscope (SEM) and Atomic Force Microscopy (AFM). The electroactive species, the 4-hydroxylaminetiophenol, was electrogenerated in situ from the 4-NTP at the modified electrode, after cycling in the potential range between 0.2 and -1.0 vs. Ag/AgCl in the first scan in 0.1 mol L-1 phosphate buffer (pH 7.0) with a scan rate of 0.02 V s-1. After activation process, the potential range around the R-NO/RNHOH redox couple was selected and cyclic voltammograms were recorded at various scan rates (5–35 mV s−1). Futhermore, the electrode modified showed an efficient electrocatalytic activity towards the oxidation of AA with oxidation overpotential of 0.15 V vs. Ag/AgCl. Electroanalytical measurements including cyclic voltammetry (CV) and chronoamperometry were used to study the behavior of the modified electrode surface employed. These techniques were used to optimize experimental parameters in order to set the best buffer, pH, and buffer concentration. Under optimized conditions, the sensor showed a linear response range (2-12 μmol L-1), LOD (0.6 μmol L-1), LOQ (2.0 μmol L-1) and sensitivity (2,8 x 10-3 μA L μmol-1). From the obtained results, the developed sensor demonstrates a promising alternative to be applied in tests with real sample