Synthesis of compact multidentate ligands to prepare stable hydrophilic quantum dot fluorophores

We describe a simple and versatile scheme to prepare an array of heterofunctional multidentate ligands that permit strong and stable interactions with colloidal semiconductor nanocrystals (quantum dots, QDs) and render them soluble in aqueous environments. These ligands were synthesized by reacting various chain length poly(ethylene glycols) with thioctic acid, followed by ring opening of the dithiolane moiety, creating a bidentate thiol motif with enhanced affinity for CdSe-ZnS core-shell QDs. Functionalization with these ligands permits processability of the nanocrystals not only in aqueous but also in many other polar solvents. These ligands provide a straightforward means of preparing QDs that exhibit greater resistance to environmental changes, making them more amenable for use in live cell imaging and other biotechnological applications.