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

CoO/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) were calculated as 0.99 s for CoO/rGO and 5.89 s for ChOx/CoO/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, 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.