Acridine Orange Stain is a cell-permeant vital dye that binds to nucleic acids. Binding to dsDNA causes acridine orange to fluoresce green and binding to ssDNA or RNA causes it to fluoresce red. Acridine Orange Stain can be used with Propidium Iodide Stain (F23003) to assess cell viability with the automated fluorescence cell counters of the LUNA™ family. Viable nucleated cells will fluoresce green and nonviable nucleated cells will fluoresce red. Due to Förster resonance energy transfer (FRET), the propidium iodide signal absorbs the acridine orange signal in nonviable cells, ensuring no double positive results