This Live or Deadâ„¢ Cell Viability Assay Kit uses two fluorescent indicators: Cellbriteâ„¢ Red (Ex/Em = 613/631 nm) for labeling viable cells and a cell-impermeable DNA-binding dye Nuclear Blueâ„¢ DCS1 (Ex/Em = 360/450 nm) for labeling dead cells with damaged membranes.