DAPI (4',6-Diamidino-2-Phenylindole, Dilactate)

DAPI (4',6-Diamidino-2-Phenylindole, Dilactate), a blue fluorescent nucleic acid stain, preferentially binds dsDNA and associates with the minor groove AT clusters. The molecular weight for DAPI is 457.5. Association of DAPI with dsDNA increases fluorescence approximately 20-fold, with an emission maximum of 460 nm. The increase in fluorescence is believed to be due to displacement of water molecules from the minor groove and DAPI. DAPI can also bind RNA and emits at a longer wavelength of 500 nm, with only a 20% increase in fluorescence.DAPI is a popular nuclear stain for identification of cell cycle and specifically stains nuclei but not cytoplasm. The dilactate form is more water soluble compared to the dihydrochloride form.DAPI can be excited by a UV laser, xenon, or a mercury-arc lamp.