Inhibition of dsDNA-Templated Copper Nanoparticles by Pyrophosphate as a Label-Free Fluorescent Strategy for Alkaline Phosphatase Assay

On the basis of the inhibition of double strand DNA (dsDNA)-templated fluorescent copper nanoparticles (CuNPs) by pyrophosphate (PPi), a novel label-free turn-on fluorescent strategy to detect alkaline phosphatase (ALP) under physiological conditions has been developed. This method relies on the strong interaction between PPi and Cu<sup>2+</sup>, which would hamper the effective formation of fluorescent CuNPs, leading to low fluorescence intensity. The ALP-catalyzed PPi hydrolysis would disable the complexation between Cu<sup>2+</sup> and PPi, facilitating the formation of fluorescent CuNPs through the reduction by ascorbate in the presence of dsDNA templates. Thus, the fluorescence intensity was recovered, and the fluorescence enhancement was related to the concentration of ALP. This method is cost-effective and convenient without any labels or complicated operations. The present strategy exhibits a high sensitivity and the turn-on mode provides a high selectivity for the ALP assay. Additionally, the inhibition effect of phosphate on the ALP activity was also studied. The proposed method using a PPi substrate may hold a potential application in diagnosis of ALP-related diseases or evaluation of ALP functions in biological systems.