Photoinduced Phase Transfer of Luminescent Quantum Dots to Polar and Aqueous Media

We report a new strategy for the photo-mediated phase transfer of luminescent quantum dots, QDs, and potentially other inorganic nanocrystals, from hydrophobic to polar and hydrophilic media. In particular, we demonstrate that UV-irradiation (lambda < 400 nm) promotes the in situ ligand exchange on hydrophobic CdSe QDs with lipoic acid (LA)-based ligands and their facile QD transfer to polar solvents and to buffer media. This convenient method obviates the need to use highly reactive agents for chemical reduction of the dithiolane groups on the ligands. It maintains the optical and spectroscopic properties of the QDs, while providing high photoluminescence yield and robust colloidal stability in various biologically relevant conditions. Furthermore, development of this technique significantly simplifies the preparation and purification of QDs with sensitive functionalities. Application of these QDs to imaging the brain of live mice provides detailed information about the brain vasculature over the period of a few hours. This straightforward approach offers exciting possibilities for expanded functional compatibilities and reaction orthogonality on the surface of inorganic nanocrystals.