Copper-Mediated DNA-Scaffolded Silver Nanocluster On-Off Switch for Detection of Pyrophosphate and Alkaline Phosphatase

We present a new copper-mediated on-off switch for detecting either pyrophosphate (PPi) or alkaline phosphatase (ALP) based on DNA-scaffolded silver nano-clusters (DNA/AgNCs) templated by a single-stranded sequence containing a 15-nt polythymine spacer between two different emitters. The switch is based on three favorable properties: the quenching ability of Cu2+ for DNA/AgNCs with excitation at 550 nm; the strong binding capacity of Cr2+ and PPi; and the ability of ALP to, transform PPi into orthophosphate (Pi). The change id, fluorescence of DNA/AgNCs depends on the concentrations, of Cu2+, PPi, and ALP. Copper(II). acts as a mediator to interact,specifically with the Probe, while PPi :and ALP convert the signal of the Probe by removing and recovering Cu2+, operating as an on-off switch: In the presence of Cu2+ only, DNA/AgNCs exhibit low fluorescence because the combination of,Cu2+ and DNA template disturbs the precise formation of DNA/AgNCs. When PPi is added to the system. containing Cu2+, free DNA template is obtained due to the stronger interaction of PPi and Cu2+, leading to a significant fluorescence increase (ON state) which depends on the concentration of PPi. Further addition of ALP results in the release of free Cu2+ via ALP-catalysis of hydrolysis of PPi into Pi, thereby-returning the system to,the low fluorescence OFF state. The switch allows the analysis of either PPi or ALP by observation-of the fluorescence status, with the detection limit of 112.69 nM and 0.005 U/mL for PPi. and ALP, respectively. The AgNCs on-off switch provides the advantages of simple design, convenient operation, and low experimental cost without need of chemical modification, organic dyes, or separation procedures.