Surface-engineered biochar-Cu-BTC hybrid for ultrasensitive dual detection of uric acid and nitrite

An electrochemical sensor was developed for the simultaneous detection of uric acid (UA) and nitrite (NO₂^-) using a hybrid nanocomposite based on juniper seed-derived biochar and copper benzene-1,3,5-tricarboxylate (CuBTC). The biochar provides a sustainable and porous carbon matrix, while CuBTC offers abundant electroactive Cu sites and enhances the electrocatalytic properties of the composite, thereby improving analyte oxidation and signal resolution. To further increase conductivity and improve interfacial charge transfer, an electrochemical activation/reduction step via cyclic voltammetry was applied. The structural and surface properties of the modified material were systematically characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), confirming successful integration of the hybrid components and their morphological compatibility. Electrochemical performance, evaluated by differential pulse voltammetry (DPV), revealed well-separated oxidation peaks for UA and NO₂^-, enabling simultaneous quantification. The sensor exhibited low detection limits of 22.6 nM for UA and 7.3 nM for NO₂^-, with two linear ranges for both analytes. High selectivity was demonstrated against common interfering species, including ascorbic acid, dopamine, glucose, hydroquinone, and inorganic ions. Analytical performance in spiked real samples showed recoveries ranging from 74.9% to 110%, with relative standard deviations below 5%, indicating acceptable accuracy and reproducibility. These results demonstrate that integrating sustainable biochar with CuBTC forms an efficient electrocatalytic interface for dual analyte detection, offering potential applications in biomedical diagnostics and environmental monitoring.