Design of a nanoswitch for sequentially multi-species assay based on competitive interaction between DNA-templated fluorescent copper nanoparticles, Cr3+ and pyrophosphate and ALP

The present work constructs a sequentially triggered nanoswitch (STN) for sequential detection of Cr 3+ , P 2 O 7 4− (PPi) and alkaline phosphatase (ALP) depending on polythymine (T40) templated fluorescent Cu nanoparticles (Cu NPs). A significant phenomenon is that Cr 3+ can only causing 5% QE of fluorescent Cu NPs synthesized by lower than 500 μM Cu 2+ , but the fluorescence of the Cu NPs synthesized by more than 500 μM Cu 2+ can be quenched up to 90% QE by the same concentration of Cr 3+ . Then the quenched fluorescence of CuNP-Cr 3+ complex provides a sensing platform for PPi due to the strong binding between Cr 3+ and PPi, resulting in dissociation of Cr 3+ from the surface of Cu NPs and the recovery of fluorescence emission . Further ALP hydrolysis of PPi disrupts Cr 3+ -PPi assemble and Cr 3+ is released to interact with Cu NPs, which induces fluorescence quenching again. Thus, sequentially detection of Cr 3+ (LOD, 0.03 μM), PPi (LOD, 0.005 μM) and ALP (LOD, 0.125 mU/mL) was successfully implemented with high sensitivity and selectivity. The sensor is also successfully used for Cr 3+ , PPi and ALP assays in the human serum. Additionally, the sensitive “on-off-on-off” sensing behavior of the Cu NPs allow three chemical inputs (Cr 3+ , PPi and ALP) to construct a logic gate.