Ultrabright, highly heat-stable gold nanoclusters through functional ligands and hydrothermally-induced luminescence enhancement

Gold nanoclusters (AuNCs) as a new class of luminescent materials have attracted a great deal of interest owing to their molecule-like properties and wide potential applications. However, limited successes have been achieved in producing intensely luminescent AuNCs. This paper reports a simple and convenient preparation method of strongly luminescent, highly heat-stable AuNCs by using functional ligands and a hydrothermal reaction. Adenosine cyclic monophosphate (cAMP) and tryptophan (Trp) are used as a template molecule and energy antenna ligand of AuNCs, respectively. By means of a common hydrothermal reaction, the resulting tryptophan-stabilized AuNCs (Trp-cAMP-AuNCs) generated surprising luminescence with a quantum yield of up to 59.6%; their luminescence is highly heat-stable, and they can be applied as a luminescent label in PCR (polymerase chain reaction) thermal cycles of DNA amplification. This unusually strong luminescence is attributed to the double effects of energy transfer from the ligand and hydrothermally-induced emission enhancement. The indole groups strongly interacting with gold atoms play an important role for the thermal-stability of the luminescence. The as-prepared AuNCs are also highly water-soluble and storage-stable. The present strategy offers a new way for and insight into the fabrication of strongly luminescent metal nanoclusters.