Developing choline oxidase immobilization on Co3O4/rGO nanohybrid surface as a high-performance biosensor for diazinon detection.

Co₃O₄/rGO nanoparticles were used to modify a glassy carbon electrode (GCE), where reduced graphene oxide (rGO) serves as an intermediate between graphene and graphene oxide, featuring a carbon framework enriched with oxygen-containing hydrophilic functional groups. The structural and morphological characterization of the modified electrode was carried out using Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS). Electrochemical performance was evaluated through cyclic voltammetry (CV) and chronoamperometry, revealing effective electron transfer between the nanoparticles and immobilized choline oxidase (ChOx). The apparent heterogeneous electron transfer rate constants (K_s) were calculated as 0.99 s^-1 for Co₃O₄/rGO and 5.89 s^-1 for ChOx/Co₃O₄/rGO. The biosensor demonstrated excellent analytical performance for choline detection, with a linear response range of 5-60 µM, a sensitivity of 0.0216 µA µM^-1, and a detection limit of 0.811 µM. Notably, the developed biosensor also exhibited a strong electrochemical response to the organophosphorus pesticide diazinon, indicating its potential for environmental monitoring. Given that diazinon is a widely used organophosphorus pesticide with high toxicity to humans and the environment, its sensitive detection is critical for monitoring and controlling pesticide contamination.