Calcein Blue AM is a membrane-permeable live-cell labeling dye. Upon entering the cell, intracellular esterases cleave the acetoxymethyl (AM) ester group, yielding the membrane-impermeable Calcein Blue fluorescent dye. Apoptotic and dead cells with compromised cell membranes do not retain Calcein Blue. Calcein Blue is optimally excited by the UV laser line (360 nm), but can also be excited by the violet laser line (405 nm) and has a peak emission of 445 nm that can be detected using filters for Pacific Blue®/eFluor® 450 (450/50). For fluorescent microscopy, it can be detected using the appropriate filter sets. Calcein Blue AM is itself weakly fluorescent, and an additional wash step may be necessary to reduce background fluorescence. Co-staining with Annexin V or 7-AAD is recommended to allow the greatest resolution between live and dead/apoptotic cells. Molecular weight: 465.41 Peak excitation: 360 nm Peak emission: 445 nm Calcein Blue AM should be reconstituted in high-quality, freshly opened DMSO. Once reconstituted, it should be stored at -20°C with dessicant and used within a short period of time. Avoid freeze-thawing.