FDA [Fluorescein diacetate] *CAS 596-09-8*

FDA is a non-fluorescent hydrophobic fluorescein derivative that can pass through the cell membrane whereupon intracellular esterases hydrolyze the diacetate group producing the highly fluorescent product fluorescein. The fluorescein molecules accumulate in cells that possess intact membranes so the green fluorescence can be used as a marker of cell viability. Cells that do not possess an intact cell membrane or an active metabolism may not accumulate the fluorescent product and therefore do not exhibit green fluorescence. FDA may be used in combination with PI staining as the non-viable cells take up the PI and stain dead cells red whereas viable cells do not take up the PI and should only stain green. This 2-color separation of non-viable and viable cells may provide a more accurate quantitation of cell viability than single color analysis.