Assembly-enhanced fluorescence from metal nanoclusters and quantum dots for highly sensitive biosensing

Fluorescent nanoparticles exhibit unique optical properties for applications in imaging and sensing. Herein, the enhancement of luminescence emission from self-assembled nanoparticles including gold nanoclusters, cadmium sulphide and near-infrared silver selenide quantum dots are reported. Addition of zinc and pyrophosphate ions induces assembly and disassembly of the particle aggregates and the corresponding intensified and recovery of fluorescence intensity, respectively. The enhancement is due to assembly-enhanced emission of metal nanoclusters and passivation of the surface trap states of quantum dots. With the hydrolysis of pyrophosphate catalyzed by alkaline phosphatase, the released zinc ions from pyrophosphate-zinc ion complexes mediate nanoparticle assembly and lead to luminescence regeneration. The assembly-induced fluorescence enhancement can be applied for sensitive assay of alkaline phosphatase with a detection limit of 3.4 pM in a continuous and real-time way. This method is capable of screening enzyme inhibitor and analyzing biological samples.