Calcein Blue, AM is a cell-permeant esterase substrate that can serve as a viability probe that measures both enzymatic activity and cell-membrane integrity, which is required for intracellular retention of their fluorescent product. Calcein blue AM is only weakly fluorescent (excitation/emission maxima ∼322/435 nm). Upon cleavage of the AM esters by intracellular esterases, this tracer becomes relatively polar and is retained by cells for several hours. In addition, its fluorescence intensity increases and its fluorescence spectra shift to longer wavelengths, with excitation/emission maxima of ∼360/449 nm.

To make a concentrated stock solution from 1–10 mM, dissolve calcein blue, AM in anhydrous high quality DMSO. Calcein blue AM is susceptible to hydrolysis when exposed to moisture. Once prepared, use the DMSO stock solutions within a short time period. Aqueous working solutions containing Calcein AM should be prepared immediately prior to use.