Know your Fluo Indicators
Three of the most popular long wavelength fluorescent calcium indicators; Fluo-2, Fluo-3, and Fluo-4; were invented by TEF Labs’ creator Akwasi Minta and by Nobel Laureate Roger Tsien at University of California Berkeley (US Patent 5049673, 1991).
Initially Fluo-3 was commercialized because of its low pKa. Fluo-4 became increasingly popular because of its greater "brightness" when excited at the 488 nm argon laser line. (Both Fluo-3 and Fluo-4 are approximately the same "brightness" when excited at their longer wavelength excitation maxima)
At 488 nm, Fluo-2 is the brightest of all, up to twice as bright as Fluo-4,most likely because its AM ester loads more readily into the cell. For their own reasons, other companies have renamed Fluo-2, for example as Fluo-8. In seeking transparency with our customers, we prefer to follow the original nomenclature: Fluo-2.
An experimental comparison of Fluo-2,3,4,and 8 can be found here.
Benefits of Fluo-2 MA:
- A direct substitute for Fluo-3 and Fluo-4
- The same molecule as Fluo-8
- Up to twice as bright as Fluo-4
- Up to four times as bright as Fluo-3
- AM ester loads well at room temperature, faster than Fluo-3 and Fluo-4
- Excitation at 490 nm, emission at 515 nm, and 390 nM Kd
- Greater than two hundred-fold increase from zero to saturated calcium