Synthesis of novel polyethyleneimine-capped silver nanoclusters exhibiting  ultraviolet-A fluorescence and their application in multiple sensing

Cupric ions (Cu²⁺), pyrophosphate (PPi), and alkaline phosphatase (ALP) are involved in a variety of biochemical processes such as DNA replication, cellular metabolism and play an important role in human growth and development. It is of great significance to establish a method for the sensitive detection of Cu²⁺, PPi and ALP. In this work, polyethyleneimine-capped silver nanoclusters (PEI-AgNCs) were successfully synthesized by a one-pot method using hydrazine sulfate as reductant, exhibiting a unique strong fluorescence emission in the near-ultraviolet region at ∼339 nm. Since the fluorescence of PEI-AgNCs can be quenched by Cu²⁺ through inner filtering effect (IFE), then recovered by competitive binding of pyrophosphate and Cu²⁺, and later weakened again by catalytic hydrolysis of alkaline phosphatase, a sensitive and selective strategy based on the changes of fluorescence "ON" or "OFF" was established to detect Cu²⁺, PPi and ALP. The LODs of these three analytes were 36 nM, 0.2 μM, and 0.14 U L⁻¹ at a S/N ratio of 3, respectively. A series of logic gate circuits for sensing cupric ions, pyrophosphate, and alkaline phosphatase were successfully constructed. The established methods have the potential for biosensing and environmental analysis and the specific UV-A fluorescence property of PEI-AgNCs may be helpful in photonic and optical areas.