Quantum optics: colloidal fluorescent semiconductor nanocrystals (quantum dots) in single-molecule detection and imaging

Coming from the electronic material sciences, semiconductor nanocrystals, called quantum dots (QDs), have emerged as new powerful fluorescent probes for in vitro and in vivo biological labeling and single-molecule experiments. QDs possess several unique optical properties that make them very attractive over conventional fluorescent dyes and genetically encoded proteins technologies. They have precise emission color tunability by size due to quantum confinement effects, better photostability and brightness, wide absorption band and very narrow emission band for multiplexing, and increased fluorescence lifetimes. These characteristics, combined with some dramatic progresses achieved in surface chemistry, biocompatibility and targeting strategies have allowed their recent advances in the field of single-molecule detection and imaging using diverse microscope geometries like confocal microscopy, total internal reflection (TIR) microscopy or basic wide-field epifluorescence microscopy. This chapter reviews the basic principles of QDs' electronic structure necessary to understand their fundamental optical and physical properties and goes on to present recent QDs' uses in biological imaging with an emphasis on single-molecule detection.