A Synergistic S-Doped WO ₃ /Hierarchical Porous Biocarbon Composite for Electrochemical Sensing of an Antiparasitic Drug Ronidazole

The extensive veterinary use of ronidazole (RZ), a nitroimidazole-class antiparasitic drug, has raised concerns regarding its environmental persistence, bioaccumulation in food products, and potential health risks. Herein, we report a highly sensitive electrochemical sensor based on a sulfur-doped tungsten oxide/hierarchical porous biocarbon (S-WO3/HPBC) composite-modified glassy carbon electrode (GCE) for selective RZ detection. S-WO3 was synthesized via a hydrothermal–ethanol crystallization–calcination route, while three-dimensional HPBC was derived from custard apple seeds through carbonization, KOH activation, and acid neutralization, providing a conductive, high-surface-area scaffold. The composite was assembled under reflux in a nitrogen atmosphere, ensuring homogeneous anchoring of S-WO3 on HPBC. The intimate integration of S-WO3 with HPBC generated a strong synergistic effect, resulting in abundant electroactive sites, accelerated charge transport, and enhanced electron-transfer kinetics. Differential pulse voltammetry revealed excellent sensing performance, with a limit of detection of 1.5 nM, a limit of quantification of 5.2 nM, and a sensitivity of 2.81 μA μM–1 cm–2. The sensor exhibited excellent repeatability, reproducibility, and selectivity, achieving recoveries of 94.6–99.91% in spiked real samples, including river water, sewage water, chicken extract, fish extract, human urine, and human blood serum. These findings highlight the synergistic contribution of S-WO3 and HPBC, establishing S-WO3/HPBC/GCE as a robust, cost-effective, and interference-free platform for reliable RZ monitoring in environmental, biological, and food matrices.