Simply stated, NO calcein AM is NOT FIXABLE. Regardless of the fixation method used - aldehyde or methanol fixation - cells stained with calcein AM will lose their staining pattern. Furthermore, calcein AM cannot be used on fixed cells because they lack the necessary esterases to convert calcein AM to calcein and the membrane integrity needed to retain the dye. Calcein AM is a fluorogenic esterase substrate and should only be used on live cells to determine cell viability.