Hyperbranched polyamine assisted synthesis of dual-luminescent gold composite with pH responsive character

We present a facile one-pot, two-step strategy to prepare water-soluble dual-luminescent gold nanodots (AuNDs) and few-atom gold nanocluster composites simultaneously by using high molecular weight and hyperbranched polyethyleneimine (hPEI) as the protection ligand and stabilization agent. It was found that in the presence of hPEI, Au(III) ion can be reduced to a metastable Au(I) charge state in aqueous solution. Subsequently, adding 11-mercaptoundonioic acid induces parallel pathways of restricted Au(I) assembly, leading to the formation of both red-emitting hPEI stabilized AuNDs and blue-emitting hPEI-protected Au₈ nanoclusters. The intensity ratio between the blue and red species shows a sensitive and reversible response to the solution pH in the range 2-11 and the dual-luminescent gold composites can act as an effective and reversible pH indicator.