What is "calcein"

n. A fluorescent dye related to fluorescein and having the chemical formula C₃₀H₂₆N₂O₁₃; used in some contexts as a calcium indicator

Calcein, also known as fluorexon, fluorescein complex, is a fluorescent dye with excitation and emission wavelengths of 495/515 nm, respectively, and has the appearance of orange crystals. Calcein self- quenches at concentrations above 70mM and is commonly used as an indicator of lipid vesicle leakage. It is also used traditionally as a complexometric indicator for titration of calcium ions with EDTA, and for fluorometric determination of calcium.