Propidium iodide *1 mg/mL aqueous solution*

Propidium iodide (PI) belongs to the same chemical class of ethidium bromide. As in the case of ethidium bromide its fluorescence is enhanced for 20-30-fold upon binding to nucleic acids. The fluorescence excitation maximum is red-shifted for 30–40 nm and the fluorescence emission maximum blue-shifted for 15 nm or so. PI also binds to RNA as DAPI and acridine orange. PI is commonly used for identifying dead cells in a population of cells and as a counterstain in multicolor fluorescent techniques. It can also be used to differentiate necrotic, apoptotic and normal cells. It is suitable for fluorescence microscopy, flow cytometry and fluorometry.