DAPI dihydrochloride (4',6-diamidino-2-phenylindole) is a fluorescent stain by binding in the minor grove of A-T rich sequences of DNA. In Vitro: DAPI (4',6-diamidino-2-phenylindole) is a DNA-specific probe which forms a fluorescent complex by attaching in the minor grove of A-T rich sequences of DNA. It also forms nonfluorescent intercalative complexes with double-stranded nucleic acids. DAPI can be used as a DNA-specific probe for flow cytometry, chromosome staining, DNA visualization and quantitation in histochemistry and biochemistry^[1].