Propidium Iodide

Propidium iodide (PI) is a membrane-impermeant nucleic acid intercalator. The dye is commonly used to selectively stain dead cells in a cell population and also used as a counterstain in multicolor fluorescent imaging.

• λEx/λEm (DNA-bound) = 535/617 nm
• λEx/λEm (no DNA) = 493/636 nm
• Orange red solid soluble in H2O or DMSO
• Store at 4°C and protect from light, especially in solution

Propidium iodide (PI) is a cell impermeable nucleic acid intercalating dye. Because PI is excluded from viable cells, it can be used to distinguish necrotic or late apoptotic cells with damaged plasma membranes from viable cells or early apoptotic cells with intact cell membranes. After entering cells and binding to DNA and RNA, the fluorescence of PI is enhanced 20- to 30-fold. PI can be used in flow cytometry and fluorescence microscopy. PI is also utilized as a counterstain in multicolor fluorescent imaging, but nuclear-specific staining requires digestion of cellular RNA.