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-2(center dot-) 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 450nm), a colorimetric analytical method was developed for TYRase determination and inhibitor screening. The assay works in the 0.5 to 2.5UmL(-1) TYRase activity range, and the limit of detection is 0.5UmL(-1). In our perception, this new assay represents a powerful approach for determination of TYRase activity in biological samples.