Live-or-Dye NucFix™ Red Viability StainLive-or-Dye NucFix™ Red is a unique, cell membrane-impermeant dye that specifically stains the nuclei of dead cells (Figure 4). Unlike other commonly used nuclear viability stains such as propidium iodide or DRAQ7™, NucFix™ labeling is extremely stable, allowing the cells to be fixed and permeabilized without loss of fluorescence or dye transfer between cells.