• Fluorescent Ca2+ indicator allows accurate measurement of intracellular calcium concentrations
  • Ratiometric readout minimizes the effects of photobleaching, leakage, uneven loading, and varying cell thicknesses in mixed populations, delivering more robust and reproducible results
  • Particularly well-suited for ratio-imaging microscopy
  • Well-established in literature, with many citations in numerous cell lines

Fura-2 is a ratiometric and sensitive indicator dye for measuring intracellular calcium. Since its introduction in 1985, fura-2 has been cited in thousands of papers that describe its applications in a wide variety of cells. These important Ca2+ indicators, developed by Roger Tsien and collaborators, have made a major contribution to advances in the understanding of the role of calcium in cellular regulation. The ability to make ratio measurements with fura-2  is an important property of this probe.

At low concentrations of the indicator, 340/380 nm excitation ratio for fura-2 allows accurate measurements of the intracellular Ca2+ concentration (Figure 1). Measuring by ratio considerably reduces the effects of uneven dye loading, leakage of dye, and photobleaching, as well as problems associated with measuring Ca2+ in cells of unequal thickness.  Measurements of fura-2 fluorescence can usually be made over a period of an hour without significant loss of fluorescence resulting from either leakage or bleaching.  In addition, fura-2 is bright enough to permit measurements at intracellular concentrations of dye unlikely to cause significant Ca2+ buffering or damping of Ca2+ transients.

Figure 1: Fluorescence excitation spectra of fura-2 (F1200F6799) in solutions containing 0–39.8 µM free Ca2+.