High Quality Content by WIKIPEDIA articles! Carboxyfluorescein succinimidyl ester (CFSE) is a fluorescent cell staining dye. CFSE is commonly confused with carboxyfluorescein diacetate succinimidyl ester (CFDA-SE), although they are not strictly the same molecule; CFDA-SE, due to its acetate groups, is highly cell permeable, while CFSE is much less so. As CFDA-SE, which is non-fluorescent, enters the cytoplasm of cells, intracellular esterases remove the acetate groups and convert the molecule to the fluorescent ester, CFSE, which is retained within cells and covalently couples, via its succinimidyl group, to intracellular molecules. Due to this covalent coupling reaction fluorescent CFSE can be retained within cells for extremely long periods. Also, due to this stable linkage, once incorporated within cells the dye is not transferred to adjacent cells.