Fluoresent reportor – an incident photon of high enough energy can be absorbed raising an electron to the excited state. The electron can recombine with a hole in the valence band and emit a photon (fluorescent light).
Fluorescence Resonance Energy Transfer – When a fluorophore or QD is close to a quencer (<10 nm), the electron at the QD can transfer its energy to the quencher without emitting the fluorescent light. The light is only emitted when the fluorophore and quencher are separted.
Molecular Beacon – single stranded DNA probe that has a stem and loop structure. The loop contains the probe sequence that is complementary to the target sequence. In the absence of targets, the probe is dark since the stem puts the fluorophore close to the quencher, but when a target is encountered, the stem hybrid dissociates, and the fluorophore and quencher are separated giving off light.