Learn how to use this product With the nucleic acid binding dyes acridine orange (AO) and propidium iodide (PI) you can accurately determine cell viability. Acridine orange is an intercalating dye that can permeate both live and dead cells. AO will stain all nucleated cells to generate green fluorescence. Propidium iodide can only enter dead cells with poor membrane intergrity, so it will stain all dead nucleated cells to generate red fluorescence. Cells stained with both AO and PI fluoresce red due to quenching, so all live nucleated cells fluoresce green and all dead nucleated cells fluoresce red. Easy AO/PI Cell Viability Assay The AO/PI Cell Viability Kit provides a convenient pre-mixed AO/PI solution that can be directly added to cell samples for cell counting and viability analysis on a fluorescent cell counter.