Synthesis of small water-soluble gold nanoparticles and their chemical modification into hollow structures and luminescent nanoclusters

Water-soluble gold (Au) nanoparticles were prepared facilely by reduction of Au(III) ions with ammonia. The pH value of Au precursor in the reaction was found to be crucial in determining the final Au nanostructures. Under acidic conditions, chain-like aggregates were formed, and these structures could be coated with a thin layer of gold by further treatment with NaBH4 to form hollow structures. On the other hand, isolated Au nanoparticles with an average size of ∼2 nm were formed under basic conditions. The modification of the as-prepared small Au nanoparticles with thiolate ligands results in luminescent Au clusters with narrow full width at half-maximum (fwhm). We suggest that the reaction undertook different pathways because of the different forms of Au(III) complex and ammonia. The as-prepared Au nanoparticles and their modification products could have potential applications in catalysis and biomedicine.