Metal-enhanced fluorescence of gold nanoclusters as a sensing platform for multi-component detection

Metal-enhanced fluorescence (MEF) has been applied to construct biosensing systems in the recent decades owing to its favorable optical properties. Herein, silver nanoparticles (AgNPs) are used to enhance fluorescence of gold nanoclusters (AuNCs), by fabricating a core-shell composite nanostructure Ag@SiO2-AuNCs consisting of a silver core, a silica shell and an outer conjugated layer of AuNCs. The core-shell MEF-capable nanoparticles possess water dispersibility, high stability and good biocompatibility. The interaction between AuNCs on the surface of the outer silica shell and the silver core, significantly improves the excitation efficiency, and thus enhances the fluorescence emission, photostability and quantum yield of the AuNCs. The composite nanoparticle Ag@SiO2-AuNCs provides a fluorescence enhancement of up to 3.21-fold when the separation distance (the thickness of the silica shell) is about 10 nm. Finally, the composite nanostructures have further been applied to develop a sensing platform for multi-component detection based on the MEF capability and the OFF-ON-OFF switching nature of the fluorescence signal, and the detection limits for Cu2+, inorganic pyrophosphate (PPi) and pyrophosphatase (PPase) are 39 nM, 78.7 nM and 0.976 mU, respectively. This platform has been applied to detect Cu2+, PPi and PPase with satisfactory results in living cells.