Highly Stable Dextran-Coated Quantum Dots for Biomolecular Detection and Cellular Imaging

Dextrans have long been used in detection and medicine, because of their low toxicity and excellent biocompatibility. Methods for attaching them to a diverse range of recognition and therapeutic molecules have been developed over many years. These properties make them ideal as coating agents for nanoparticles with applications in detection, imaging, and medicine. In this report, we show that semiconductor quantum dots (QDs) coated with dextrans are highly luminescent, and stable, under a wide range of conditions in the presence of reagents and metabolites such as those which are commonly encountered in biological detection and imaging. Stability is monitored by Forster resonance energy transfer (FRET) titrations with fluorescent avidin, and their use under physiological conditions is demonstrated by tracking their progress in living cells. The surface chemistry is not disrupted by physiological (10 mM) concentrations of glutathione, making them compatible with intracellular environments. Dextran-coated QDs conjugated to streptavid in bind only to the surface of cells that have been biotinylated. These results show that the advantageous properties of dextrans can be extended to QDs and their application to single-cell imaging.