A cell-permeable, non-fluorescent acetoxymethyl ester derivative of Calcein that gets hydrolyzed inside the cell by esterases. The loss of the acetoxymethyl group also enables calcein to readily bind intracellular calcium resulting in a strong yellowish-green fluorescence. It is the best probe for cell viablilty and cell adhesion due to its greater retention in cells as well and its pH insensitivity in physiological range. MW: 994.86. Purity ≥95% by HPLC