Fluorescent gold nanoclusters: synthesis and recent biological application

Fluorescent gold nanoclusters (AuNCs) have been extensively studied due to their unique construction and distinctive properties, which place them between single metal atoms and larger nanoparticles. The dimension of AuNCs is comparable to the Fermi wavelength of electrons, which lead to size-dependent fluorescence and other molecule-like properties. In this review, we summarize various synthesis strategies of fluorescent AuNCs and recent advances of biological applications such as biosensing, biolabeling, and bioimaging. The synthetic methods are considered as two routes: "Atoms to Clusters" and "Nanoparticles to Clusters." The surface functionalization of AuNCs is described as the precondition for making future bioapplications possible, which can eventually influence their stability, biocompatibility, and other properties. And then we focus on the recent advances of AuNCs-based applications in biological sensing, biolabeling, and bioimaging and finally discuss the current challenges of AuNCs in controllable synthesis and biological application.