Quantum dots (QDs) are nano-scale semiconductor particles on the order of 2–10 nm in diameter. They possess electrical properties between those of bulk semi-conductors and individual molecules, as well as optical characteristics that make them suitable for applications where fluorescence is desirable, such as medical imaging. Most QDs synthesized for medical imaging are in the form of CdSe(ZnS) core(shell) particles. CdSe QDs have been shown to possess optical properties superior to organic dyes. The ZnS shell has a two-fold effect:
# to interact with dangling bonds that would otherwise result in particle aggregation, loss of visual resolution, and impedance of quantum confinement effects
# to further increase the fluorescence of the particles themselves.