Monitoring the activity and inhibition of alkaline phosphatase via quenching and restoration of the fluorescence of carbon dots

We report that the fluorescence of carbon dots (C-dots) in water is quenched by the addition of Cu2+ ions, and that the subsequent addition of pyrophosphate (PPi) restores fluorescence. This is likely to be due to the coordination of Cu2+ by PPi. This effect forms the basis for a method to determine the activity and inhibition of the enzyme alkaline phosphatase (ALP). If ALP is added to a system composed of C-dots, Cu2+ and PPi, fluorescence will decrease over time because ALP catalyzes the hydrolysis of PPi to form orthophosphate (Pi). This results in a release of the quencher Cu2+. The decrease in fluorescence is related to the activity of ALP. The method is simple and displays good sensitivity (with a limit of detection of 1 units per L) and selectivity. The method was successfully applied to the determination of ALP in serum samples. We also have studied the inhibitory effect of Pi on the activity of ALP. We presume that this method holds a large potential in terms of diagnosis of ALP-related diseases, to evaluate the function of ALP in biological systems and in screening for potential inhibitors of ALP.