Annexin V-APC/7-AAD Apoptosis Kit is possible to differentiate cells at various stages of apoptosis and distinguish dead cells Annexin V is a calcium-dependent phospholipid-binding protein which specifically binds to phosphatidylserine (PS) Under normal conditions PS is located on the inner surface of the cell membrane lipid bilayer but during early apoptosis PS translocates from the inner leaflet to the outer leaflet of the plasma membrane becoming exposed to the extracellular environment By using Annexin V-APC labeling apoptotic cells can be detected easily through flow cytometry or fluorescence microscopy within 15-30 minutes Additionally this kit contains the nuclear dye 7-AAD a fluorescent probe that specifically binds double-stranded DNA emitting red fluorescence Normally 7-AAD cannot permeate intact cell membranes However cells in the late apoptotic or necrotic stages exhibit compromised membrane integrity allowing 7-AAD to enter and stain the nuclei