5-Carboxyfluorescein diacetate, acetoxymethyl ester (CFDA, AM) is a cell-permeant esterase substrate that can serve as a viability probe that measures both enzymatic activity, which is required to activate its fluorescence, and cell-membrane integrity, which is required for intracellular retention of their fluorescent product. Upon hydrolysis by intracellular esterases, CFDA, AM yields the 5-carboxyfluorescein product that gives bright green fluorescence when excited with a blue light or the common 488 nm Argon laser. It is often used to monitor cell viability or label live cells for cell analysis.