Calcein-AM is a fluorescent dye commonly used in biological research to assess cell viability and function. It is a non-fluorescent compound that can easily penetrate live cells. Once inside, cellular esterases convert it into the fluorescent form, calcein, which emits green fluorescence when excited by light. This property makes calcein-AM a valuable tool for studying living cells in various applications, including cell culture, drug testing, and toxicology. Researchers can visualize and quantify live cells using fluorescence microscopy or flow cytometry, providing insights into cellular health and behavior.