Calcein AM is widely used in cell biology for assessing cell viability. It is a membrane-permeable dye that, upon entering live cells, is hydrolyzed by intracellular esterases to produce calcein, a green fluorescent compound. This fluorescence indicates cell viability, as only living cells with active esterases can convert Calcein AM into its fluorescent form. It is commonly employed in flow cytometry, fluorescence microscopy, and high-throughput screening assays to monitor cell health, proliferation, and cytotoxicity. Additionally, Calcein AM is used in co-staining experiments with other dyes, such as propidium iodide, to distinguish between live and dead cells. Its non-toxic nature and ease of use make it a valuable tool in biomedical research and drug discovery.