Synthesis of thiol-stabilized monodispersed gold nanoclusters with narrow near-infrared fluorescence emission

We have successfully prepared monodispersed fluorescent ultra-small Au nanoclusters (about 2 nm) via a two-phase liquid–liquid method. The products are extremely stable and can be dissolved in toluene in any concentration without agglomeration, even be stored in air for months. This stability is mainly attributed to the surfactant dodecanethiol whose operative part is the Au–S bond. On the Au nanocluster surface, the Au–S group makes the particles exclude each other to form the monodispersed stable Au nanocluster. The products did not exhibit surface plasmon absorption owing to their insulating molecular state. At the same time, they emitted near-infrared extreme narrow fluorescent emission spectrum under 370 nm excitation. Here, dodecanethiol also plays an important role to enhance the fluorescent intensity due to charge transfer from surface ligands to gold. Because of their superiority in stability and sharp emission peak, Au nanoclusters appear to be an attractive fluorescent material for bioimaging and biological marker.