Development and investigation of a NiO/ZnO@PPy-modified glassy carbon electrode for electrochemical sensing of metronidazole in environmental samples: Experimental and DFT studies

Metronidazole (MTZ) is widely prescribed as an antimicrobial drug, and its extensive use in animal farming has led to its accumulation in the environment, posing significant risks to human health and the environment. In this study, nickel and zinc oxide (NiO/ZnO) composite materials were incorporated with polypyrrole (PPy) on a modified glassy carbon electrode (GCE) to fabricate a NiO/ZnO@PPy/GCE sensor for the electrochemical reduction of MTZ in tap water and river water samples. The physicochemical and structural properties of the NiO/ZnO@PPy composite were analyzed using XRD, FT-IR, Raman spectroscopy, SEM, and EDS. In addition, the molecular chemical reactivity of MTZ molecules was investigated using density functional theory (DFT)-based reactivity descriptors. The fabricated NiO/ZnO@PPy/GCE sensor exhibited excellent electrochemical performance for MTZ detection, with electrochemical experiments conducted using differential pulse voltammetry (DPV) and cyclic voltammetry (CV) in PBS at pH 7. The sensor achieved a low limit of detection (LOD) of 0.2368 μM, a wide linear concentration range of 2–300 μM, and a high sensitivity of 3.5166 μA/μM·cm 2 , along with remarkable reproducibility, repeatability, and stability. Furthermore, the real-world applicability of the developed sensor was evaluated through real-sample analysis of tap and river water, yielding satisfactory recovery rates ranging from 97.6578% to 98.3394%. These results indicate that the developed NiO/ZnO@PPy/GCE sensor represents a promising strategy for the reliable quantification of MTZ in real environmental applications.