Oxygen Vacancy-Enriched NiO Nanozymes Achieved by Facile Annealing in Argon for Detection of L-Cys

Abstract

Nickel oxide (NiO) nanozyme, as an excellent oxidase mimic, have been widely used in fluorescence biological detection, water pollutant analysis, food safety and cell imaging. However, to fully achieve these applications, it is still a great challenge to regulate its crystalline micro/nanostructure and composites to achieve high enzyme activity and high specific surface area. Here, we applied a very simple thermal annealing treatment to restructure the calcined precursor of NiO. Importantly, it was found that oxygen vacancy (O_V) concentration of the targeted NiO nanozyme is significantly increased while the annealing atmosphere is argon rather than air. Moreover, the as-prepared novel NiO sample (NiO-O_V) nanosheets achieved ca. 2-fold enhancement in specific surface area. It is believed that the higher O_V concentration and the larger specific surface area will increase the enzyme activity by accelerating electron transfer rate and increasing catalytic interfaces. The significant improvement of enzyme activity of NiO-O_V was verified by the fluorescence "turn-on" experiment of Amplex red (AR). Finally, using NiO-O_V/AR system, we constructed a highly sensitive enzyme sensor on L-Cys with a detection limit of 37.8 nM. It also displayed an excellent specificity for ten typical amino acid interferences.