Disulfide-functionalized hyperbranched poly(amidoamine) derivatives as both reductant and stabilizer for the synthesis of fluorescent gold nanoclusters

Hyperbranched polymers were successfully used as reductant and stabilizer for the synthesis of stable water-soluble fluorescent gold nanoclusters (AuNCs) through a one-step bottom-up strategy. The hyperbranched polymers having such performance were acetamide terminated hyperbranched poly(amidoamines) (HPA-Acs) with disulfide functional groups. Small sized (less than 2   nm) AuNCs were formed under the optimal conditions of 80   °C, weak acidic condition (around pH 4.3) for 15–20   h. Through adjusting the feed ratio of HAuCl 4 to HPA-Ac, the emitting light could be tuned from yellow to near-infrared. The measurements of UV–vis spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy further verified the formation of AuNCs. The quantum yields of the yellow and near-infrared fluorescent AuNCs were ca. 3.6% and 1.2%, respectively. The as-prepared AuNCs showed an excellent stability in a wide pH range (pH 2–12) and possessed low cytotoxicity for cancer HeLa cell, making it a suitable candidate for bioimaging.