Colorimetric determination of the activities of tyrosinase and catalase via substrate-triggered decomposition of MnO2 nanosheets

The authors describe novel colorimetric assays for tyrosinase (TYR) and catalase (CAT) based on the substrate-triggered decomposition of MnO 2 nanosheets (NSs). The MnO 2 NSs can act as oxidase mimics that catalyze the oxidation of the substrate tetramethylbenzidine (TMB) to form a blue dye with an absorption maximum at 652 nm. The oxidase-mimicking activity of the MnO 2 NSs is inhibited by dopamine (DA)/hydrogen peroxide (H 2 O 2 ) due to their decomposition of the MnO 2 NSs. TYR catalyzes the oxidation of DA while CAT can decompose H 2 O 2 into water and oxygen. Therefore, the oxidase-mimicking activity of MnO 2 NSs is restored in the presence of both enzymes and their substrates. Based on the competitive consumption of substrates between enzymes and MnO 2 NSs, a colorimetric method for determination of enzyme activity and its substrate is developed. The detection limits for TYR and CAT are 6 mU·mL −1 and 33 mU·mL −1 , respectively. A colorimetric method for monitoring enzyme activity and its substrate is described. It is based on the substrate-inhibited oxidase-mimicking activity of MnO 2 nanosheets.