Annexin V-PE/DAPI Apoptosis Kit enables differentiation between early apoptotic late apoptotic and dead cells Annexin V is a Ca2 -dependent phospholipid-binding protein that specifically binds to phosphatidylserine (PS) PS is normally located on the inner leaflet of the cell membrane phospholipid bilayer However during the early stages of apoptosis PS moves from the inner surface to the outer surface of the cell membrane becoming exposed to the extracellular environment Labeled with a fluorescence dye such as PE Annexcin V is commonly used as a fluorescent probe to detect apoptosis through flow cytometry or fluorescence microscopy within 15-30 minutes Additionally this kit includes the nuclear stain DAPI which specifically binds to double-stranded DNA to emit blue fluorescence Normally DAPI cannot penetrate intact cell membranes In late apoptotic and dead cells DAPI can cross the compromised membrane to stain the nucleus