Electrochemical Sensor Fabrication Based on Nanocomposite of ZIF-8/ZnO Decorated with Poly(L-Cysteine) for Trace Analysis of Morphine

The carbon paste was boosted with a nanocomposite of ZIF-8 and ZnO nanoparticles and used for the fabrication of a modified electrode named ZIF-8, ZnONP/CPE. Then, a thin film of poly L-cysteine was electrodeposited on its surface. The synthesized nanomaterials and modified electrode were characterized by utilizing scanning electron microscopy, FT-IR, and X-ray diffraction techniques. The electrochemical behavior of morphine was studied using fabricated electrodes by cyclic and differential pulse voltammetry methods. Evaluating the pH effect on morphine oxidation at ZIF-8, ZnONP/CPE revealed a two electrons-one proton reaction. Based on Tafel slope the electron transfer coefficient equal to 0.6 was obtained. The diffusion coefficient of 1.75 x 10- 5 cm2/s was calculated for morphine by applying Cottrell's relation on the chronoamperogarms current. The optimized electrochemical parameters resulted in the outstanding performance of the developed sensor for detecting morphine, encompassing a broad linear range from 9 nM to 250 mu M and achieving a low detection limit of 1 nM.