Most useful and inexpensive lasers operate in the green part of the visible spectrum and that has made green-emitting fluorescent calcium indicators very useful for confocal microscopy, flow cytometry, and screening. The popular green-emitting fluorescent calcium indicators for screening are Fluo-2, Fluo-3, Fluo-4, and Fluo-8. They are all derived from the original Fluo compound invented by Minta and Tsien (1989).

Fluo-3 has been used to image the spatial dynamics of Ca2+ signaling, in flow cytometry experiments involving photoactivation of caged chelators, second messengers, and neurotransmitters, and for cell-based pharmacological screening. Fluo-4 is an analog of Fluo-3 with the two chlorine substituents replaced by fluorines, which results in increased fluorescence excitation at 488 nm and consequently higher fluorescence signal levels. Cells may be loaded with the AM ester forms of these calcium indicators by adding the dissolved indicator directly to dishes containing cultured cells.

The patent for Fluo-2, Fluo-3, and Fluo-4 have expired so Ion Indicators offers these at reasonable prices.

Dye Characteristic Comparison

Reagents for viability and Toxicity Assays