Aggregation of Metal-Nanoparticle-Induced Fluorescence Enhancement and Its Application in Sensing.

Fluorescence-based detection methods have been widely utilized in various applications. Materials that display aggregation-induced emission (AIE) are excellent fluorescence probes to offer high contrast ratio. Chromophore-conjugated plasmonic metal nanoparticles (NPs) have been recently found to display significantly enhanced fluorescence emission upon the formation of aggregates. This new type of AIE enhancement has a totally different working mechanism. It is based on aggregation-induced plasmon coupling of metal NPs to enhance the fluorescence intensity of chromophores by increasing both the excitation efficiency and radiative decay rates, instead of reducing nonradiative decay rates as in typical AIE. AIE enhancement of chromophore-conjugated metal NPs results in a dramatic change in fluorescence intensity from severely quenched fluorescence to significantly enhanced fluorescence upon aggregate formation. It offers excellent contrast ratio and is attractive for developing platforms for highly sensitive sensing and imaging applications with reduced background. This mini-review summarizes the basic working principle and recent progress in fluorescence enhancement by coupled metal NPs on the single-molecule level, aggregation-induced plasmon coupling enhanced fluorescence of chromophore-conjugated metal NPs, and their applications in sensing. Perspectives on further utilization of this interesting phenomenon for various biomedical applications have also been discussed.