Annealing Temperature-Dependent Photoelectrochemical Property of Zinc Oxide/Graphene Nanocomposite and the Application for Fabricating a “Signal-Off” Photoelectrochemical Aptasensing for ATP

Designing a sensitized structure to improve the inherent performance of photoactive materials is an effective strategy for improving the sensitivity of "signal-off" photoelectrochemical (PEC) aptasensing. Here, we present a facile thermal-treatment route for fabricating ZnO/graphene sensitized structure (ZnO/GR nanocomposite) via using zinc sulfate and graphene oxide (GO) as starting materials. The PEC performance of ZnO/GR nanocomposite can be controlled by the annealing temperature. It was found that the annealing temperature greatly affects the phase transition and nanocrystallite size of the prepared nanostructure. X-ray diffraction (XRD) showed that ZnO began to form at the decomposition temperature of 530 °C, indicating that the existence of GO can greatly decrease the decomposition temperature of zinc sulfate from 930 °C to 530 °C. The morphology characterization illustrated an increase in the average ZnO nanoparticles (ZnO NPs) nanocrystallite size from $\sim $ 30 to $\sim $ 100 nm when the annealing temperature was varied from 530 °C to 700 °C. Furthermore, we investigated the PEC behavior of these different nanostructures obtained under various temperatures, and the significant photocurrent intensity of ZnO/GR nanocomposite was also obtained at the annealing temperature of 700 °C because the well distributed and increased crystallite size can reduce the recombination rate of electron–hole pairs on the ZnO/GR nanocomposite thin films. Finally, a "signal-off" PEC sensor was designed for adenosine triphosphate (ATP) detection based on a ZnO/GR-700 °C nanocomposite as photoactive materials and an ATP-binding aptamer as the recognition element. This "signal-off" PEC aptasensor exhibited a wide linear range from 5 to 3000 nM with a low detection limit of 1.66 nM.