Basic principles of FRAP, FLIM and FRET

Stokes identified the phenomenon of fluorescence in the mid 19 century, and the first fluorescence microscopes were developed at the beginning of the 20th Century. These were used to study autofluorescence in organic and inorganic compounds. Imaging of secondary fluorescence (whereby specific tissues and bacteria which did not autofluoresce were labeled with a fluorescent marker and subsequently imaged) was developed in the 1930’s by Haitigen, and by the 1950’s, Koons and Caplan were using fluorescence microscopy to observe the location of antigens labeled with a fluorophoretagged antibody (Wang and Lansing Taylor, 1989).