Waste-derived nanocomposite carbon paste electrochemical sensor for the first guadipyr monitoring in agri-environmental samples: a sustainable platform for on-site analysis

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A portable electrochemical sensing platform was developed for the determination of guadipyr (GUA) in agri-environmental and food matrices as a sustainable alternative to conventional chromatographic methods. To the best of our knowledge, this is the first electrochemical sensor reported for GUA monitoring. The sensing interface was fabricated using a carbon paste electrode modified with multi-walled carbon nanotubes (MWCNTs) and aluminum oxide nanoparticles (Al₂O₃-NPs) synthesized from recycled aluminum foil waste, integrating waste-valorization principles into sensor fabrication. Structural and electrochemical characterization confirmed the successful construction of a highly active nanocomposite interface with enhanced conductivity and charge-transfer properties. The electrochemical behavior of GUA was investigated by cyclic voltammetry and differential pulse voltammetry, revealing a well-defined irreversible cathodic peak at - 0.68 V (CV) and - 0.67 V (DPV) in Britton-Robinson buffer (BRB) (pH 5.0), corresponding to the reduction of the nitro group. Under optimized conditions, the proposed sensor exhibited a linear response over the concentration range of 0.5-35 µM with a detection limit of 0.067 µM. The method was successfully applied for GUA determination in tomato, river water, irrigation water, and soil samples using matrix-matched calibration, providing satisfactory recoveries and high precision. Sustainability assessment using MA, CFA, NQS, and SAMI metrics confirmed the eco-friendly nature of the method. The developed platform offers a rapid, low-cost, and field-deployable strategy for routine GUA monitoring.