Preparation of water-soluble, PEGylated, mixed-dispersant quantum dots, with a preserved photoluminescence quantum yield

High quantum yields, colloidal stability and surfaces amenable to diverse chemical modifications are critical objectives for quantum dot (QD) synthesis. We present an approach of QD preparation developed for achieving these criteria. In addition, the nascent QDs are already water-soluble. We then partially exchanged the N-acetyl cysteine (NAC) ligands on our core–shell–shell CdTe/CdS/ZnS QDs for dithiol-poly(ethylene glycol) (dithiol-PEG). This resulted in mixed-dispersant QDs with photoluminescence properties rivaling those of QDs synthesized under high temperature conditions and modified by ligand exchange using dithiol-PEG. Optimization of the dithiol-PEG adsorption conditions not only retained efficient surface passivation by NAC as well as luminescence properties, but also resulted in sufficiently dense PEG-grafting to confer strong colloidal stability. Since particle properties such as solubility and protein resistance critically depend on the PEG conformation and density, we also evaluated the effects of various adsorption and grafting conditions on the polymer, using ATR-FTIR and TGA analysis. Leakage of cadmium ions from the core is prevented by the ZnS-shell, which is stabilized by the remnant NAC and physicochemically shielded by the PEG-layer. Furthermore, the residual NAC has carboxylic groups that can in principle still be chemically-modified with diverse functional groups. These characteristics, particularly their excellent solubility in water, render our QDs compatible for use in biomedical and environmental applications.