Propidium iodide (PI) is a nuclear staining dye that binds to double stranded DNA, which then illuminates the nucleus of a dead cell. It is a popular red-fluorescent dye to detect dead cells since it is membrane impermeant and therefore not visible in live cells. PI is commonly used in different applications such as flow cytometry, fluorescence microscopy, fluorometry, and confocal laser scanning microscopy and is compatible with other dyes.