Annexin V is a Ca2 dependent phospholipid-binding protein that specifically binds to phosphatidylserine (PS) Normally PS resides on the inner surface of the cell membrane s phospholipid bilayer During early stages of apoptosis it translocates from the inner leaflet to the outer surface thus exposing itself to the extracellular environment Cy5-labeled Annexin V can serve as a fluorescent probe to detect apoptosis using flow cytometry or fluorescence microscopy within 10-20 minutes SYTOX Green is a non-cell-permeable cyanine fluorescent dye and stains only dead cells It can be used effectively to differentiate normal viable cells from necrotic cells For cells at late apoptotic stages or dead cells SYTOX Green can penetrate the disordered regions of cell membrane reach the cell nucleus embedding into the DNA double helix to form a SYTOX Green-DNA complex resulting in a 500-fold increase of fluorescence intensity with bright green fluorescence