The LIVE/DEAD™ FungaLight™ Yeast Viability Kit enables researchers to easily, reliably and quantitatively distinguish live and dead yeast in minutes by flow cytometry. The kit contains solutions of the SYTO 9 green-fluorescent nucleic acid stain and the red-fluorescent nucleic acid stain, propidium iodide. These stains differ both in their spectral characteristics and in their ability to penetrate healthy yeast cells. When used alone, the SYTO 9 stain generally labels all yeast in a population - those with intact membranes and those with damaged membranes. In contrast, propidium iodide penetrates only yeast with damaged membranes, causing a reduction in the SYTO 9 stain fluorescence by fluorescence resonance energy transfer (FRET) when both dyes are present. As a result, yeast with intact membranes stain fluorescent green, whereas yeast with damaged membranes stain fluorescent red.

Any physiological buffer between pH 7.0–8.0, including PBS, can be used to dilute the SYTO dyes for the staining solution.