A turn-on colorimetric detection of tyrosinase activity with manganese-doped cerium oxide nanozyme

A sensitive colorimetric detection toward tyrosinase activity was developed. Rod-shaped manganese-doped cerium oxide (Mn/CeO₂) nanozyme was synthesized via a simple hydrothermal process. This nanocomposite exhibited a peroxidase-like activity, effectively accelerating the conversion of a colorless chromogenic substrate TMB (3,3',5,5'-tetramethylbenzidine) into a blue product. It was found that a substrate for tyrosinase, catechol, significantly inhibited this catalysis and the subsequent color change. The further introduction of tyrosinase facilitated an oxidation of catechol into a benzoquinone product, thereby eliminating the inhibition and restoring the nanozyme's catalysis. This response presented a turn-on colorimetric signal toward tyrosinase in the range 1-3000 U/L, with a detection limit at 0.3 U/L. Furthermore, the proposed method was successfully applied to the analysis of practical samples.