A small heterobifunctional ligand provides stable and water dispersible core-shell CdSe/ZnS quantum dots (QDs)

We describe a simple method to prepare water dispersible core-shell CdSe/ZnS quantum dots (QDs) 1 capping QDs with the new thiol-containing heterobifunctional dicarboxylic ligand 4 (DHLA-EDADA). This ligand, obtained in gram scale through few synthetic steps, provides a compact layer on the QDs, whose hydrodynamic size in H2O is 15 nm ± 3 nm. The colloidal stability is drammatically enhanched with respect to the well-known (±) ?-Lipoic acid (DHLA). The ligand affinity towards QDs and the water dispersibility of nanocrystals 1 are addressed by the dithiols groups of DHLA, that chelate the Zinc of the shell, and by the dicarboxylic groups of the ethylenediamine-N,N-diacetic acid residue (EDADA), respectively. The effects of pH, buffer solutions, and biological medium on QDs 1 stability were assessed by monitoring the photoluminescence (PL) and hydrodynamic size over time. Highly fluorescent QDs dispersions, stable over extended periods of time and over broad pH ranges and buffer types, were obtained. Furthermore, we show that the DHLA-EDADA ligand 4 also endows QDs with functional groups suitable for further conjugation and for metal ions detection. As a case study to illustrate the potential of our approach, we report the preparation and characterization of a highly luminescent orange emitting polymer-QDs 1