Phosphatidylserine (PS) is translocated from the inner to the outer surface of the cell for phagocytic cell recognition. The human anticoagulant, Annexin V, is a 35 kDa Ca2+-dependent phospholipid protein with a high affinity for PS. Annexin V labeled with CF488A (Abs/Em= 490/515 nm) can identify apoptotic cells in green by binding to PS exposed on the outer leaflet. Our CF488A dye is superior to fluorescein/FITC as it is not affected by pH and has much better photostability. Moreover, 7-AAD emits in the far-red spectrum and can be well separated from CF488A and other green emitting dyes using the 488nm line of a flow cytometer. 7-AAD is impermeant to live cells or apoptotic cells, but stains necrotic cells with red fluorescence (Abs/Em with DNA = 543/655 nm).
