Exploring the potential of linear polymer structures for the synthesis of fluorescent gold nanoclusters

Abstract

In this study, fluorescent gold nanoclusters (AuNCs) were synthesized via the one-pot reduction of gold ions (Au³⁺) in the presence of thiolated copolymers. Well-defined copolymers, which are comprised of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) and 2-(acetylthio)ethyl methacrylate (AcSEMA) monomers in either a block or random structure, were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization. Following deprotection of the AcSEMA thioester pendant group to yield a thiol, the formation of gold nanoclusters was performed at various relative molar concentrations of thiol to gold ions in order to investigate the effect on the fluorescent properties. Random copolymer stabilized gold nanoclusters (R@AuNCs) displayed higher emission intensity in comparison to block copolymer stabilized gold nanoclusters (B@AuNCs). In aqueous media, the hydrodynamic diameter of B@AuNCs (10.4–13.4 nm) were relatively larger compared to the R@AuNCs (5.9–6.6 nm) as determined by dynamic light scattering (DLS). However, the AuNCs cores were estimated to be similar in size according to the Jellium model (≅0.49 nm, ∼Au₂₅), indicating the negligible effect of different polymer structure on the size of the fluorescent AuNCs core. Interestingly, these nanoclusters displayed linear temperature-dependent fluorescence emission intensity (≅0.7% °C⁻¹) which may be important in biosensing applications.