La-Dy ₂ O ₃ /MWCNT: Vacancy-Engineered Electrode for Electrochemical Detection of Metol in Environmental and Biofluid Samples

This work describes the fabrication of an electrochemical sensor constructed upon La-doped Dy2O3 and multiwalled carbon nanotube (MWCNT) composite for the sensitive and selective detection of N-methyl-p-aminophenol sulfate (metol, MTL), a representative aromatic pollutant of environmental and toxicological relevance. The La-Dy2O3/MWCNT nanocomposite was synthesized via a hydrothermal method and the structural, morphological, and compositional properties were systematically investigated through scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray powder diffraction (XRPD). Electrochemical evaluation by cyclic voltammetry (CV), square-wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) confirmed the superior electrocatalytic performance of the composite-modified glassy carbon electrode (GCE), arising from the synergistic effects of La3+ doping and the high electrical conductivity of the MWCNT network. Periodic density functional theory (DFT) calculations were employed to investigate dopant-induced modifications in the bulk electronic structure, while molecular DFT provided insight into the redox behavior of MTL underlying the observed electrochemical response. The sensor exhibited a wide linear response range (0.3–220 μM), a low detection limit of 0.1 μM, and high sensitivity (0.387 μA μM–1 cm–2), with kinetic analyses indicating a diffusion-controlled, proton-coupled electron transfer mechanism and optimal performance at pH 7.0. Furthermore, the sensor demonstrated excellent reproducibility (RSD = 3.06%), repeatability (RSD = 3.35%), and operational stability over 15 days, along with strong anti-interference capability and high recovery values in complex matrices, including tap water, river water, artificial urine, and human serum, without the need for pretreatment or sophisticated instrumentation, highlighting its potential as a reliable, field-deployable, and cost-effective platform for environmental and clinical monitoring of electroactive aromatic contaminants.