Depositing reduced graphene oxide on ZnO nanorods to improve the performance of enzymatic glucose sensors

The improvement of enzymatic glucose sensors, which have outstanding advantages such as high sensitivity, good selectivity, and convenient operation, is crucial because of the increasing demand for the diabetics detection. Here, we prepared the ZnONRs-based glucose sensor by hydrothermally synthesizing the ZnO nanorods (ZnONRs) on a flexible PET substrate. The electrodeposited reduced graphenes (rGO) with different deposition cycles were coated onto the ZnONRs to modify the surface of working electrodes. The high conductivity of rGO promoted the transmission of redox electrons, which significantly improved electron transport between solution and electrode. Also, the rGO smoothed the rough surface of the working electrodes, which negligibly increased the contact angles, reduced the contacting surface area between the working electrodes and the PBS solution, and further decreased the enzyme adsorption that influences the redox electron yield. Nevertheless, the former positive effect was more significant than the latter negative one, which eventually gave rise to better performance of the rGO/ZnONR-based glucose sensors. Thereby, in the Nafion/GOx/rGO-20/ZnONRs/Au/PET sensors, the sensitivity increased by 9.2 times, the detection limit decreased by 47 times, and the linear range was extended from 7.5 mM to 12 mM, compared with sensors without rGOs. Additionally, both of the ZnONRs-based and rGO/ZnONRs-based glucose sensors show strong anti-interference performance in the test environment containing urea, uric acid, and ascorbic acid.