Switchable fluorescence of gold nanoclusters for probing the activity of alkaline phosphatase and its application in immunoassay

In this work, a novel strategy for modulating the fluorescence of gold nanoclusters (Au NCs) is developed. The fluorescence of bovine serum albumin (BSA) protected Au NCs is firstly quenched by KMnO4 and then restored by ascorbic acid (AA) due to the deterioration/restoration of the surface structure. Based on which, a novel “switch–on” fluorescent assay for probing the activity of alkaline phosphatase (ALP) is developed with a detection limit as low as 0.002U/L. In addition, this testing protocol is also expanded to the detection of the inhibitor of ALP and mouse IgG (as a model), the detection limits are 15ng/mL for the inhibitor of 2,4–Dichlorophenoxyacetic acid (2,4–DA) and 1.5pg/mL for mouse IgG. The present method paves a new way to develop convenient, sensitive, and selective metal NCs–based fluorescent “turn–on” probes with promising applications in versatile biosensing. •First example of modulating the fluorescence of Au NCs by chemical redox strategy.•“Switch-on” fluorescence assay for probing the activity of ALP based on Au NCs.•This method had ultra-sensitivity, acceptable reproducibility and good selectivity.•This method could be extended readily for versatile biological affinity reactions.