Calcein

Calcein (also known as fluorexon) is a fluorescent derivative of fluorescein. Calcein AM (acetoxymethyl calcein), a non-fluorescent derivative, functions as a cell-permeant substrate of active cellular esterases. Only living cells are able to hydrolyze the acetoxymethyl group from calcein AM to produce fluorescent calcein, which emits green fluorescence. Calcein AM is useful for cell viability studies, and is suitable in flow cytometry and imaging applications. The dye has an excitation wavelength around 495 nm and an emission wavelength around 515 nm.