Calcein is a fluorescent dye commonly used in biological and chemical research. It is known for its ability to stain living cells, allowing scientists to visualize cellular structures and processes under a fluorescence microscope. Calcein emits a bright green fluorescence when excited by specific wavelengths of light, making it useful for various applications, including cell viability assays and tracking cellular activities. In addition to its use in research, calcein can also be employed in environmental studies to assess the health of aquatic ecosystems. It helps in detecting the presence of certain ions and can indicate the viability of organisms in water samples, contributing to the understanding of environmental science and ecotoxicology.