The Annexin V Apoptosis Detection Kit includes Annexin V (Catalog #100-0329 or Catalog #100-0333 or Catalog #100-0331), Annexin V Binding Buffer (Catalog #100-0334), and 7-AAD (Catalog #75001). The kit is used for the combined detection of early-stage cell apoptosis (using Annexin V) and late-stage cell apoptosis or necrosis (using both Annexin V and 7-AAD).

Annexin V belongs to the annexin family of intracellular proteins that bind to membrane phospholipids in a calcium-dependent manner. This dye has a high affinity for phosphatidylserine (PS) that is present in the inner leaflet of the plasma membrane. During early-stage cell apoptosis, PS is translocated from the inner to the outer leaflet of the cell membrane, exposing it to the external environment, where it is detected by Annexin V. This process of PS translocation occurs prior to the loss of membrane integrity. As cells progress through apoptosis and towards necrosis, the cell membrane is compromised and consequently the 7-AAD viability dye passes into the cell. Thus, cells undergoing early apoptosis stain positive for Annexin V and negative for viability dyes, while apoptotic death or necrosis is characterized by positive staining for both Annexin V and 7-AAD.