The bright red color fluorescent reagent for detecting of the early stages of apoptosis. During apoptosis, phosphatidylserine (PS) is translocated from the cytoplasmic face of the plasma membrane to the cell surface. Annexin V has a strong, Ca²ᶧ-dependent affinity for PS and therefore serves as a probe for detecting apoptosis. The Annexin V-Cy3 conjugate contains the bright red fluorescent probe that can be used for detection of apoptosis by fluorescence microscopy with a rhodamine filter or by flow cytometry. Cy3 yields red fluorescence with a λmax emission of 570 nm.