Propidium iodide (or PI) is a fluorescent intercalating agent that can be used to stain cells and nucleic acids.

PI binds to DNA by intercalating between the bases with little or no sequence preference.

[1] Propidium iodide is used as a DNA stain in flow cytometry to evaluate cell viability or DNA content in cell cycle analysis, [2] or in microscopy to visualize the nucleus and other DNA-containing organelles.

Propidium Iodide is not membrane-permeable, making it useful to differentiate necrotic, apoptotic and healthy cells based on membrane integrity.

[5] PI is widely used in fluorescence staining and visualization of the plant cell wall.