Annexin V-Biotin Assay Kit (ab273267) is based on the observation that soon after initiating apoptosis, most cell types translocate the membrane phospholipid phosphatidylserine (PS) from the inner face of the plasma membrane to the cell surface. Once on the cell surface, PS can easily bind to Biotin-conjugated Annexin V, a protein that has a strong natural affinity for PS. Annexin V-Biotin can be detected in conjunction with conventional dye-staining using any streptavidin- or avidin-dye reagents, such as (strept)avidin-fluorescein, -peroxidase, -alkaline phosphatase (AP), and -β -gal, etc