A Fluorescence “off-on-off” sensing platform based on bimetallic gold/silver nanoclusters for ascorbate oxidase activity monitoring
Herein, papain-protected bimetallic gold/silver nanoclusters (Au/Ag NCs) was successfully synthesized and applied for the detection of ascorbate oxidase (AAO). The doping of papain-protected Au nanoclusters with Ag could enhance the fluorescence intensity and display an intense red fluorescence peak at 617 nm, and the red-emitting Au/Ag nanoclusters were further used to monitor AAO activity. The fluorescence of Au/Ag NCs could be quenched by hydrogen peroxide (H2O2) due to the generation of hydroxyl radical (•OH) between the reaction of Ag/Au nanoclusters and H2O2. However, the addition of ascorbic acid (AA) could effectively react with free radicals and cause the fluorescence recovery of the Au/Ag NCs. Furthermore, AAO could catalyze the oxidation of AA to form dehydro-ascorbate (DHA), as a result, there was not enough AA to consume hydroxyl radical, which resulted in the decrease of the fluorescence of papain-capped Au/Ag NCs. Therefore, AAO activity can be monitored by measuring the fluorescence intensity of the red-emitting Au/Ag NCs. Moreover, the developed detection method for AAO detection displayed a good linear relationship from 5 to 80 mU mL-1 and the detection limit is 1.72 mU mL-1. Thus, a simple and selective method for the determination of AAO activity was constructed and obtained satisfactory results in real samples detection.