Active site-tuned high peroxidase-like activity nanozyme for on-the-spot detection of saliva total antioxidant capacity using smartphone devices.

Metal-Organic Framework (MOF) based nanozymes with clear structure are beneficial for exploration of structural-performance and exhibit broad prospects in improving activity. In this study, the prepared bimetallic FeNi-MOF nanozyme was superior to single metal MOF in the peroxidase-like activity. Subsequently, a derivative nanozyme (FeNi-MOF-Ar) was prepared by pyrolysis using FeNi-MOF as the precursor in argon atomoshere with controlled temperature. The investigated of FeNi-MOF-Ar revealed that the irregular macroporous state and the presence of heterovalent Fe/Fe sites of FeNi-MOF-Ar enable the retention, exposure, and electronic structure regulation of active sites, promoting the dual mechanism (the generation of •OH and electron transfer mechanism) and significantly increasing the peroxidase-like activity. FeNi-MOF-Ar exhibited a strong affinity for substrate HO, which is higher than horseradish peroxidase. Ascorbic acid and cysteine are typical substances of antioxidants. FeNi-MOF-Ar was used for sensitive colorimetric detection of ascorbic acid and cysteine, and the detection limit was as low as 150 and 60 nM. In addition, the smartphone devices was used to detection of antioxidant equivalent ascorbic acid, with a detection range of 0.5-120 μM. FeNi-MOF-Ar nanozyme is feasible for sensitive detection of saliva total antioxidant capacity.