Molecular crowding-modulated fluorescence emission of gold nanoclusters: Ligand-dependent behaviors and application in improved biosensing

[Display omitted] •Fluorescence emission of GSH-GNCs and BSA-GNCs is modulated by molecular crowding.•Molecular crowding triggers the aggregation-induced enhanced emission of GSH-GNCs.•Molecular crowding promotes the interaction between GSH-GNCs and protamine.•An efficient method for detection of protamine and heparin is developed. In this work, we found that the fluorescence emission and sensing performance of gold nanoclusters (GNCs) could be modulated greatly under molecular crowding environment in a ligand-dependent manner. The fluorescence emission of glutathione-protected GNCs (GSH-GNCs) can be significantly improved by molecular crowding while that of bovine serum albumin (BSA)-capped GNCs is notably weakened. Further, it was observed that molecular crowding could facilitate the interaction between GSH-GNCs and protamine, thus triggering a synergetic aggregation-induced enhanced emission (AIEE) effect. The AIEE could be suppressed by subsequent addition of heparin, allowing the development of a simple and efficient fluorescence approach for determination of protamine and heparin. The proposed method presents detection ranges of 0.7–3.0 and 0.05–2.8 μg mL−1 for protamine and heparin with the detection limits of 7.5 and 1.7 ng mL-1, respectively. This work is the first study of how molecular crowding impacts the fluorescence emission of GNCs and their interaction with biomolecules. The results indicate that the modulated properties of GNCs in crowding condition may open new prospects for the development of GNCs-based sensing methods.