Cayman's 7-AAD Cell Viability Assay employs 7-AAD as a fluorescent label for dead cells. 7-AAD is a fluorescent dye that is excluded from live cells but penetrates dead or damaged cells to label DNA. Although 7-AAD fluorescence is less intense than that of propidium iodide, it exhibits a higher wavelength emission maximum (excitation at 488 nm, emission at 650 nm) and thus has minimal spectral overlap with PE or FITC. This makes 7-AAD preferable as a viability marker when FITC and/or PE are used simultaneously to label surface or intracellular antigens.