Rational design of an innovative hybrid biosensor utilizing functionalized ZnO-Cys-graphene ternary composite for enzyme-free glucose detection

Abstract

The limitations of enzymatic sensors for glucose detection have been addressed through the development of non-enzymatic sensors utilizing Zinc Oxide (ZnO). ZnO is an attractive choice due to its favourable properties, including cost-effectiveness, catalytic activity, large surface area, high adsorption capacity, and biocompatibility, which make it well-suited for glucose sensing applications. To enhance sensing performance, L-Cysteine, a low molecular weight amino acid, was employed as a capping agent for ZnO, leveraging its functional groups to improve the sensor's adsorption capacity and sensitivity. Additionally, graphene, a two-dimensional carbon material with excellent conductivity and surface area, was incorporated into the composite of cysteine-capped ZnO (ZnO-Cys), resulting in a ZnO-Cysteine-Graphene (ZnO-Cys-GNS) composite. This incorporation aimed to further enhance the sensing properties of the biosensor. The final products ZnO, ZnO-Cys, ZnO-Cys-GNS were characterized by XRD, SEM, TEM, FTIR and Raman spectroscopy to analyse its structure and morphology. CV and chronoamperometry were used for electrochemical measurements to evaluate the glucose detection capabilities of the materials. The results demonstrated ZnO-Cys-GNS composite showed higher activity towards glucose detection and exhibits sensitivity of 161.12 μA/(mM.cm2) and lower detection limit of 0.663 μM with wide linear detection range from 0.01 mM to 1 mM. The utilization of non-enzymatic sensors based on metal oxides, such as ZnO, and the incorporation of functional molecules like L-Cysteine and graphene overcome the limitations associated with enzymatic sensors, offering a more stable and efficient approach for glucose detection.