Peptide-coated semiconductor nanocrystals for biomedical applications.

We have developed a new functionalization approach for semiconductor nanocrystals based on a single-step exchange of surface ligands with custom-designed peptides. This peptide-coating technique yield small, monodisperse and very stable water-soluble NCs that remain bright and photostable. We have used this approach on several types of core and core-shell NCs in the visible and near-infrared spectrum range and used fluorescence correlation spectroscopy for rapid assessment of the colloidal and photophysical properties of the resulting particles. This peptide coating strategy has several advantages: it yields probes that are immediately biocompatible; it is amenable to improvements of the different properties (solubilization, functionalization, etc) via rational design, parallel synthesis, or molecular evolution; it permits the combination of several functions on individual NCs. These functionalized NCs have been used for diverse biomedical applications. Two are discussed here: single-particle tracking of membrane receptor in live cells and combined fluorescence and PET imaging of targeted delivery in live animals.