Yeast Viability Kit 1 is used to analyze the cell concentration and viability of yeast samples with the automated fluorescence cell counters of the LUNA™ family. Fluorescein Diacetate Stain and Propidium Iodide Stain for Yeast are used to assess cell viability. Viable cells hydrolyze fluorescein diacetate into the green fluorescent compound fluorescein, causing viable cells to fluoresce green. Not being able to permeate intact cell membranes, propidium iodide is taken up by nonviable cells and cells with compromised membranes binding to the nucleus of nonviable cells and causing them to fluoresce red. Fluorescence Signal Enhancer 1 is an inhibitor of ATP-dependent fluorescein efflux. By blocking fluorescein from being pumped out of the cell, Fluorescence Signal Enhancer 1 lowers background and increases signal intensity, thereby enhancing the fluorescein signalto-noise ratio. Fluorescence Signal Enhancer 1 is most effective with metabolically active cells in the log growth phase. Cell Dilution Buffer is for washing cells and diluting cell suspensions