Dual-Analyte Selective Electrochemical Detection of Phenylbutazone and Sulfamethoxazole Using Bio-Engineered Bi₂S₃-ZnO Nanocomposites

Simultaneous sensing and quantification of pharmaceutically active compounds (PhACs) are crucial for protecting the environment and maintaining long-term ecological sustainability. This study focuses on the bio-based synthesis of Bi₂S₃-ZnO nanocomposites (Bi₂S₃-ZnO(bio)) using Sechium edule bio-extract for dual-analyte selective and simultaneous electrochemical monitoring of phenylbutazone (PBZ) and sulfamethoxazole (SMZ) in the environmental matrices. Bi₂S₃-ZnO(bio) exhibited ZnO(bio) nanostructures embedded on Bi₂S₃(bio) nanorods with an average rod length of 1409.7 nm and a smaller crystal size of 14.43 nm. After immobilization of Bi₂S₃-ZnO(bio) onto the glassy carbon electrode (Bi₂S₃-ZnO(bio)/GCE), a 94.6% reduction in charge transfer resistance, a 63.2% rise in electroactive surface area, and a 76.5% enhancement in anodic peak response were observed than bare/GCE. The oxidation of PBZ and SMZ proceeded by releasing two electrons each, with a rate constant (k⁰) of 0.907 s^-1 for PBZ and 0.721 s^-1 for SMZ. For simultaneous sensing, the Bi₂S₃-ZnO(bio)/GCE achieved the limit of detections (LODs) of 0.222 and 0.089 μM with sensitivities of 0.116 and 0.296 μA μM^-1 cm^-2 for PBZ and SMZ, respectively, within a linear range of 0.25-120 μM. The presence of interference could not interfere with the electrochemical sensing of PBZ and SMZ, and only a decrease in peak response of 12.9% for PBZ and 11.8% for SMZ was observed after 10 reuse cycles during the simultaneous sensing. The developed simultaneous sensing platform could efficiently detect and quantify PBZ and SMZ in real water samples, achieving about 100% recovery.