Blending of HAuCl4 and histidine in aqueous solution: a simple approach to the Au-10 cluster

Water-soluble, monodispersed, and bluish green-emitting Au-10 nanoclusters were synthesized through a simple reaction, in which histidine served as both a reducing agent and a protecting ligand. UV-visible absorption, photoluminescence, electrospray ionization (ESI) mass spectrometry, and X-ray photoelectron spectroscopy (XPS) were carried out to demonstrate the chemical composition and optical properties of the Au-10 clusters. The mechanism of this proposed reaction was explored and the reducing ability of histidine was proved from its imidazole group. Finally, the fluorescence of Au NCs at different reaction times, pH value, and temperature was measured in situ. Then a synthetic strategy was proposed for gold nanoclusters with a defined chemical composition, and the resulting Au-10 clusters stabilized by histidine are biocompatible with bioorganisms, showing a great potential for applications such as biological labeling and biosensors.