Fura-2

Fura-2 is a ratiometric fluorescent dye which binds to free intracellular calcium. It was the first highly used dye for calcium imaging and remains very popular. Fura-2 is excited at 340 nm and 380 nm of light, and the ratio of the emissions at those wavelengths is directly correlated to the amount of intracellular calcium. The use of the ratio allows freedom from a myriad of confounding factors, such as dye concentration, autofluorescent background, focus drift and ambient light, making Fura-2 one of the most preferred tools to quantify calcium levels. More recently, genetically encoded calcium indicators based on spectral variants of the green fluorescent protein, such as Cameleons, have supplemented the use of Fura-2 and other small molecule dyes for calcium imaging.