Determination of tyrosinase activity with manganese dioxide nanosheet-assisted fluorescence

Tyrosinase is an enzyme in the process of melanin formation and relates to the occurrence of freckles, brown spots, or excessive deposition of melanin in human body and other diseases. In this work, a turn-on fluorescence detection toward tyrosinase was developed. Manganese dioxide nanosheets were conveniently synthesized as an oxidizing agent. These nanosheets converted non-fluorescent o-phenylenediamine (OPD) into a fluorescent product. This reaction and the related fluorescence could be inhibited by reductive dopamine. When tyrosinase was introduced, it catalyzed the oxidation of dopamine and thus led to a recovery of the fluorescence. This signaling provided enhanced fluorescence responses toward tyrosinase in the range 0.006–0.08 U/mL, with a detection limit at 0.003 U/mL. The scheme was successfully applied onto practical samples. Graphical abstract