Illustration of quantum dots being synthesised and attached to antibodies (y-shaped) to allow them to bind to cellular targets. Quantum dots are nanocrystals of semiconductor material that emit photons when excited. The size of the quantum dot can be tuned during synthesis to produce a certain wavelength of photon emission. Antibodies are part of the human immune system. They recognise specific antigens, such as molecules on a cells surface, and bind to them.