Annexin V staining is a laboratory technique used to detect early stages of apoptosis, or programmed cell death, in cells. This method utilizes a protein called Annexin V that binds to phosphatidylserine, a lipid normally found on the inner leaflet of the cell membrane. During apoptosis, phosphatidylserine is translocated to the outer membrane, allowing Annexin V to attach and signal the presence of dying cells. The staining process typically involves labeling Annexin V with a fluorescent dye, enabling visualization under a fluorescence microscope. This technique is widely used in cell biology and medical research to study the mechanisms of cell death and the effects of various treatments on cell viability.