The influence of substrates addition order on colorimetric assay based on MnO nanocubes: A novel turn-off HO assay strategy in water-soak foods.

Herein, novel MnO nanocubes were facilely synthesized by manipulating the dosage of KMnO and l-Dopa with the aid of ultrasound. The as-prepared MnO nanocubes exhibited interesting oxidation activity which was influenced by the addition order of substrates (HO and 3,3,5,5-tetramethylbenzidine (TMB)). After the mechanism study, we found that HO and TMB can be competitively oxidized by MnO nanocubes, which was different from the peroxidase- and oxidase-like activities. According to the discovery, a novel turn-off HO assay method based on MnO nanocubes was established, where HO was firstly incubated with MnO nanocubes for 3 min and then TMB was added for the instantaneous chromogenic reaction. In addition to the shorter operation time, the colorimetric results were less affected by temperature and unchanged within 30 min without terminating reaction. Moreover, the method showed ultra-high sensitivity with low limit of detection (0.027 μmol L) and acceptable reliability for HO assay in water-soak foods.