Synthesis, optical properties and applications of ultra-small luminescent gold nanoclusters

Luminescent gold nanoclusters (AuNCs), composed of a few to about 100 gold atoms, have attracted considerable attention due to their molecule-like properties. These include the discrete electronic states and size-dependent fluorescence resulting from their size, which is comparable to the Fermi wavelength of conduction electrons. AuNCs have proved to be ideal fluorescence labels for biological applications and environmental monitoring and surveillance, thanks to an attractive set of features (e.g., ultra-small size, good biocompatibility and excellent photostability). This article covers in detail the synthesis strategies and optical properties, and highlights recent advances in analytical and biological applications of water-soluble luminescent AuNCs. We also discuss the potential challenges facing luminescent AuNCs in making breakthroughs in synthesis and biological applications.