Colorimetric tyrosinase assay based on catechol inhibition of the oxidase-mimicking activity of chitosan-stabilized platinum nanoparticles.

It is found that catechol inhibits the oxidase-mimicking activity of chitosan-protected platinum nanoparticles (Chit-PtNPs) by competing with the substrate for the active site of the Ch-PtNPs. The inhibition mechanism of catechol is different from that of ascorbic acid in that it neither reacts with O nor reduces the oxidized 3,3',5,5'-tetramethylbenzidine (TMB). Tyrosinase (TYRase) catalyzes the oxidation of catechol, thus restoring the activity of oxidase-mimicking Chit-PtNPs. By combining the Chit-PtNP, catechol, and TYRase interactions with the oxidation of TMB to form a yellow diamine (maximal absorbance at 450 nm), a colorimetric analytical method was developed for TYRase determination and inhibitor screening. The assay works in the 0.5 to 2.5 U·mL TYRase activity range, and the limit of detection is 0.5 U·mL. In our perception, this new assay represents a powerful approach for determination of TYRase activity in biological samples. Graphical abstract Schematic representation of a colorimetric method for tyrosinase (TYRase) detection and inhibitor screening. It is based on the fact that catechol can inhibit the oxidase-like activity of chitosan-stabilized platinum nanoparticles (Ch-PtNPs) by competing with the substrate for the active sites and TYRase can catalyze the oxidation of catechol.