Eletrodos baseados em grafeno obtidos por gravação a laser: eletroanálise de amostras ambientais, biológicas e de alimento

Abstract

Laser engraving has emerged as a promising technique for the rapid, simple, and low-cost fabrication of electrochemical sensors. In this thesis, laser-induced graphene (LIG) electrodes were fabricated through the direct engraving of polyimide using a CO₂ laser, aiming at the development of electrochemical methods for applications in food, environmental, and biological samples. To achieve this goal, the work was conducted in three stages. Initially, using unmodified LIG electrodes, a method was developed for the determination of total antioxidant capacity (TAC) in tea samples through the quantification of the consumption of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, employing batch injection analysis (BIA) with amperometric detection. The method exhibited a linear range from 2 to 900 μmol L⁻¹, a limit of detection (LOD) of 0.6 μmol L⁻¹, and high precision (relative standard deviation, RSD < 4.0%). The TAC of the samples followed the order: mixed tea < black tea < green tea < green tea with hibiscus, in agreement with the conventional spectrophotometric method. In a second stage, the applicability of these unmodified devices was extended to the determination of chloramphenicol in honey samples by adsorptive stripping differential pulse voltammetry (AdSDPV). This method showed linearity in the range of 10 to 160 μmol L⁻¹, an LOD of 1.0 μmol L⁻¹, and recovery values ranging from 86% to 109%. Finally, it was demonstrated, for the first time, that the application of only 3.0 μL of dimethyl sulfoxide (DMSO) onto the surface of LIG electrodes significantly enhances the electrochemical activity of the material. Physicochemical and electrochemical characterizations revealed changes in the chemical composition, structure, and surface morphology of LIG, including an increased concentration of oxygen-containing functional groups, structural reorganization favoring the formation of graphitic domains, enhanced hydrophilicity, increased surface roughness, and reduced charge-transfer resistance. Based on this surface modification strategy, a method was developed for the determination of sulfanilamide in water and synthetic urine samples using differential pulse cathodic stripping voltammetry (DPCSV). The method exhibited a linear response in the range of 0.3 to 9.0 μmol L⁻¹, an LOD of 0.09 μmol L⁻¹, and recovery values ranging from 90% to 104%. Overall, the results demonstrate that LIG-based electrodes constitute a versatile, efficient, and low-cost analytical platform. Furthermore, surface treatment with DMSO proved to be a simple and effective strategy for enhancing the electrochemical performance of LIG, thereby expanding its potential for the development of electrochemical sensors.