Semiconductor quantum dots for molecular and cellular imaging

Biological probes are indispensable tools for studying biological samples, cells in culture, and animal models. Exogenous probes are frequently multifunctional, having one component that can detect a biological molecule or event, and another component that reports the presence of the probe. A fundamental example of this functionality is a fluorescently labeled antibody: when administered to a monolayer of fixed cells, the antibody binds to its target molecule, and the fluorophore emits light to signal its presence. Of the many available reporters (e.g., radioactive isotopes, chromophores, and fluorophores), fluorescent molecules have been found to be invaluable due to their inherently high sensitivity of detection, low cost, ease of conjugation to biological molecules, and lack of ionizing radiation. Indeed, organic fluorophores and fluorescent proteins have been used in nearly all avenues of biological sensing, from in vitro assays to living animal imaging. Recently, quantum dots (QDs) have been developed as a new class of biological fluorophore. With easily tunable properties and significant spectral advantages over conventional fluorophores, QDs have already been used for ultrasensitive biological detection.