The influence of substrates addition order on colorimetric assay based on MnO2 nanocubes: A novel turn-off H2O2 assay strategy in water-soak foods

Herein, novel MnO2 nanocubes were facilely synthesized by manipulating the dosage of KMnO4 and L-Dopa with the aid of ultrasound. The as-prepared MnO2 nanocubes exhibited interesting oxidation activity which was influenced by the addition order of substrates (H2O2 and 3,3,5,5-tetramethylbenzidine (TMB)). After the mechanism study, we found that H2O2 and TMB can be competitively oxidized by MnO2 nanocubes, which was different from the peroxidase-and oxidase-like activities. According to the discovery, a novel turn-off H2O2 assay method based on MnO2 nanocubes was established, where H2O2 was firstly incubated with MnO2 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 termi-nating reaction. Moreover, the method showed ultra-high sensitivity with low limit of detection (0.027 mu mol L-1) and acceptable reliability for H2O2 assay in water-soak foods.