Fluorescence Lifetime Imaging Microscopy Analysis of Isolated Melanosomes.

Melanosomes are organelles found in a wide variety of tissues throughout the animal kingdom. They contain a variety of biological molecules, but the dominant constituent is the pigment melanin, and many functions ascribed to melanosomes, such as photoprotection, are uniquely enabled by the chemical properties and structures of the melanins they contain. In this report, fluorescence lifetime imaging microscopy (FLIM) is used, for the first time, to examine fluorescent properties of pigments in melanosomes and evaluate their time evolution upon extended laser irradiation. A relatively short-lived component is discovered in fluorescence emission and significant changes in lifetimes upon irradiation are revealed indicating structural photoinduced changes to melanin occurring on a time scale of minutes, with observations extending up to 1 h.