Fluo-3 is essentially nonfluorescent unless bound to Ca2+ and exhibits a quantum yield at saturating Ca2+ of 0.14 and a Kd for Ca2+ of 390 nM.

Fluo-3 (ammonium salt) is a fluorescent calcium indicator commonly used in flow cytometry and cell-based experiments to detect changes in intracellular calcium levels. Its absorption maximum at 506 nm makes it compatible with excitation at 488 nm by argon-ion laser sources. Fluo-3 provides intense fluorescence upon...