Green design of magnetic biochar/hydroxyapatite nanocomposite-modified carbon paste electrode for sensitive dopamine detection

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In this work, we developed an electrochemical sensor for dopamine (DA) detection using a carbon paste electrode (CPE) modified with a biochar/hydroxyapatite/Fe₃O₄ (BC/HA-Fe₃O₄) nanocomposite. The nanocomposite was synthesized using a simple, eco-friendly method. The structural, morphological and magnetic properties of the material were characterized by FTIR, FESEM, XRD, BET and VSM. Electrochemical studies using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that the modified electrode has better electrical conductivity and faster electron transfer compared to the unmodified CPE. The electrochemical behavior of dopamine was investigated using CV and differential pulse voltammetry (DPV). Under optimized conditions, the sensor showed a linear response in the concentration range of 0.01–660 μM. The limit of detection (LOD) and limit of quantification (LOQ) were calculated as 4.0 nM and 10.0 nM, respectively. The sensor exhibited good repeatability (RSD = 2.05% for intra-day measurements) and reproducibility (RSD = 2.5% for inter-day measurements). It also showed high selectivity toward dopamine in the presence of common interfering substances. The sensor was used to measure dopamine in pharmaceutical formulations and human serum samples with satisfactory recovery results (97–103%), indicating its potential for practical applications.

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