In vivo detection of superoxide anion in bean sprout based on ZnO nanodisks with facilitated activity for direct electron transfer of superoxide dismutase

Here, we report on a novel superoxide anion (O₂ ^•-) biosensor based on direct electron transfer of copper, zinc-superoxide dismutase (Cu, Zn-SOD) at zinc oxide nanodisks surface for in vivo tracking of O₂^•- in bean sprouts. Direct electron transfer of SOD is achieved at ZnO nanodisks film prepared by a one-step electrodeposited method, with a high heterogeneous electron rate constant of 17 ± 2 s^-1. Spectroscopic data demonstrate that SOD strongly immobilized onto the nanostructured ZnO surfaces processes its inherent activity toward O₂^•- dismutation. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SOD substantially provides a dual electrochemical approach to determination of O₂^•- with high selectivity, wide linear range, long stability, and good reproducibility. In particular, SOD adsorbed on the ZnO nanodisks film is capable of sensing O₂^•- cathodically at a very positive potential, 0 mV (vs Ag|AgCl), where the common interfering species such as hydrogen peroxide, uric acid, ascorbic acid, and 3,4-dihydroxyphenylacetic acid were effectively avoided. The excellent analytical performance of the present O₂^•- biosensor, combined with the remarkable characteristics of nanostructured ZnO films, such as biocompatibility, ease of preparation, and facile to miniaturize, paves an electrochemical way for reliable and durable in vivo determination of O₂^•- in bean sprouts.