Soft-binding ligand-capped fluorescent CdSe/ZnS quantum dots for the facile labeling of polysaccharide-based self-assemblies

In this research, soft-binding aminopropanol (APP) was employed as an efficient ligand, for the transfer of as-prepared hydrophobic CdSe/ZnS quantum dots (QDs) into polar solvents. It was found that the ligands at the surface of the original QDs could be completely replaced by APP after a phase-transferring process which successfully maintained fluorescence properties and original morphology of the QDs. The resulting intermediate QDs were soluble in common polar organic solvents, such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and tetrahydrofuran (THF), and the soft-binding ligand could be easily removed by exposure to water. Taking advantage of the excellent solubility of the APP-capped QDs and the soft-binding characteristics of APP, a novel reaction-free method was investigated for the fluorescent labeling of polysaccharide-based micelles via encapsulation of the intermediate QDs. The incorporation of QDs had little effect on the size of the micelles and did not elevate their cytotoxicity. A photo-induced fluorescence enhancement effect was observed for the incorporated QDs, and the QD-labeled micelles could be used for cell imaging. The concept of soft-binding ligand capped QDs and the reaction-free fluorescent labeling method can be applied to a wide range of QD studies.