AO/PI Staining Solution contains two DNA fluorescent dyes Acridine Orange (AO) and Propidium Iodide (PI) AO is able to cross intact cell membranes and label nuclei in all cells (both live and dead) emitting green fluorescence In contrast PI can penetrate only compromised cell membranes thus staining exclusively the nuclei of dead cells emitting red fluorescence This staining solution is optimized for use with fluorescence-based cell counters to accurately count cells Traditional Trypan Blue staining has low specificity often leading to inaccurate counting results due to the inclusion of cell debris or residual red blood cells in PMBC samples Since AO and PI are DNA-specific dyes their use effectively eliminates interference from impurities and red blood cells enabling precise and accurate cell counting