A highly specific and sensitive fluoresceing DNA stain used in epifluorescent microscopy to observe structures containing DNA. DAPI specifically binds to double stranded DNA, and when excited with light the DAPI-DNA complex fluoresces a bright blue (Porter & Feig 1980).
DAPI or 4',6-diamidino-2-phenylindole is a fluorescent stain that binds strongly to DNA. It is used extensively in fluorescence microscopy. Since DAPI will pass through an intact cell membrane, it may be used to stain live and fixed cells.