Calcein 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 fluorescent dye. Apoptotic and dead cells with compromised cell membranes do not retain Calcein. Calcein is optimally excited at 495 nm and has a peak emission of 515 nm. For fluorescent microscopy, Calcein can be detected using the appropriate filter sets. For flow cytometric analysis, it can be excited off the blue laser line (488 nm) and detected using filters for FITC/Alexa Fluor® 488 (530/30). For multicolor flow cytometry, concentrations in the range of 5 – 20 nM are recommended to ensure that compensation can be performed successfully. Co-staining with Annexin V or 7-AAD is recommended to allow the greatest resolution between live and dead/apoptotic cells. If single-color analysis is desired, improved resolution between live and dead/apoptotic cells may be obtained by using either Calcein Blue AM (cat. 65-0855) or Calcein Violet 450 AM (cat. 65-0854). Molecular weight: 994.86 Peak excitation: 495 nm Peak emission: 515 nm Calcein 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.