DNA-templated silver nanoclusters for fluorometric determination of the activity and inhibition of alkaline phosphatase

The authors describe a fluorometric assay for determination of the activity and inhibition of alkaline phosphatase (ALP). It is based on the use of silver nanoclusters (AgNCs) templated with dC(12) strands and acting as a fluorescent probe. The fluorescence of such AgNCs is initially quenched by the addition of Cu(II) in low concentration, and then recovered by the subsequent addition of pyrophosphate (PPi) due to strong binding between PPi and Cu(II). In the presence of ALP, PPi will be hydrolyzed to form phosphate ion (Pi), and this decreases the concentration of bound Cu(II). As a result, the fluorescence of AgNCs is diminished again. The decrease in fluorescence intensity is proportional to the actual activity of ALP. The assay has a detection limit as low as 0.078 mU center dot mL(-1). The method was applied to the determination of ALP activity in spiked human serum and gave recoveries that ranged from 96.2% to 105.9%. The inhibitory effect of L-phenylalanine on the activity of ALP was also evaluated. The assay is simple and inexpensive. In our perception, it simplifies clinical measurement, thereby improving the diagnosis of ALP-associated diseases and improving the screening for new drugs.