Fluorescence in the life sciences
Fluorescence is widely used in the life sciences as a powerful and minimally invasive method to track and analyze biological molecules in real-time. Some proteins or small molecules in cells are naturally fluorescent, which is called intrinsic fluorescence or autofluorescence (such as NADH, tryptophan or endogenous chlorophyll, phycoerythrin or green fluorescent protein).
Source: Wikipedia — Fluorescence in the life sciences (CC BY-SA 4.0)