DESENVOLVIMENTO DE SENSORES ELETROQUÍMICOS BASEADOS EM MATERIAIS NANOESTRUTURADOS E HÍBRIDOS PARA DETECÇÃO DE FLOROGLUCINOL E L-CISTEÍNA

Abstract

Phloroglucinol (FG) is a phenolic compound of relevance in pharmaceutical, environmental, and industrial applications, whereas L-cysteine (L-CIS) is a biologically important amino acid associated with metabolic processes and widely used as a biomarker in clinical analyses. In this context, the development of sensitive and selective analytical methods for the determination of these species is of great interest. In this work, electrochemical sensors based on glassy carbon electrodes modified with nanostructured and hybrid materials were developed for the sensitive and selective detection of FG and L-CIS. For FG determination, a sensor composed of multi-walled carbon nanotubes (MWCNTs), carboxyl-functionalized cadmium telluride quantum dots (CdTe-COOH), and chitosan (CTS) was proposed. The combination of these materials promoted a synergistic effect, resulting in a significant enhancement of the electrochemical response in phosphate buffer solution (PBS, pH 7.5). The sensor exhibited, by linear sweep voltammetry (LSV), a linear range from 1 to 2000 µmol L⁻¹ and a limit of detection of 0.8 µmol L⁻¹. By differential pulse voltammetry (DPV), two linear ranges were observed, from 0.05 to 250 and from 250 to 1000 µmol L⁻¹, with a limit of detection of 0.03 µmol L⁻¹. Selectivity, repeatability, and reproducibility studies confirmed the robustness of the device, with relative standard deviation (RSD) values of 1.72% for repeatability and 2.56% for reproducibility. The applicability was demonstrated in water and artificial urine samples, with recoveries ranging from 104.6% to 107.7% and from 97.7% to 101.6%, respectively. For L-CIS determination, a second sensor was developed using a glassy carbon electrode modified with MWCNTs, trimetallic oxides (Fe₂O₃–MgO–CuO), and Nafion. Morphological analyses indicated the formation of aggregated structures with nanostructured characteristics. Under optimized conditions (PBS, pH 7.5) and using linear sweep voltammetry (LSV), the sensor exhibited a significant improvement in charge transfer kinetics and electrocatalytic performance. The analytical response showed a linear dependence on the logarithm of L-CIS concentration, with two linear ranges (0.5–100 and 100–1000 µmol L⁻¹) and high correlation coefficients (R² ≥ 0.990). The detection limit was 0.004 µmol L⁻¹. Repeatability and reproducibility tests yielded RSD values of 1.58% and 1.82%, respectively, while selectivity studies demonstrated good tolerance toward potential interferents. The applicability of the sensor was confirmed for the determination of L-CIS in artificial plasma and human urine samples, with recoveries ranging from 106.00% to 108.82% and from 96.43% to 103.08%, respectively, demonstrating high accuracy even in complex matrices.