Oxygen vacancy-enriched NiO nanozymes achieved via facile annealing in argon for detection of l-Cys†

Abstract

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