Propidium Iodine

Propidium iodide reagent is used for the fluorescent staining of nucleic acids. Propidium iodide (PI) binds to DNA by intercalating between the bases with little or no sequence preference and with a stoichiometry of one dye per 4-5 base pairs of DNA. PI also binds to RNA, necessitating treatment with nucleases to distinguish between RNA and DNA staining. Once the dye is bound to nucleic acids, its fluorescence is enhanced 20- to 30-fold, the fluorescence excitation maximum is shifted ~30-40 nm to the red and the fluorescence emission maximum is shifted ~15 nm to the blue. Although its molar absorptivity (extinction coefficient) is relatively low, PI exhibits a sufficiently large Stokes shift to allow simultaneous detection of nuclear DNA and fluorescein-labeled antibodies, provided the proper optical filters are used. Propidium iodide is suitable for fluorescence microscopy, confocal laser scanning microscopy, flow cytometry and fluorometry.

Propidium iodide is a fuorescent stain for nucleic acids. Cell membrane integrity excludes propidium iodide from staining viable and apoptotic cells. Propidium iodide may be used in flow cytometry to evaluate cell viability when used with other dyes that stain viable cells or cells that are early in the apoptosis process.