In contrast to single-wavelength indicators such as Fluo-4, the absorption (or fluorescence excitation) maximum of Fura indicators shifts from 380 nm (Fura-2), 415 nm (Fura-8™ and Fura-10™) for the Ca2+-free chelator to about 340 nm (Fura-2), 355 nm (Fura-8™ and Fura-10™) for the Ca2+-bound .