What are ratiometric dyes?

Ratiometric dyes are a subcategory of fluorescent dyes that are widely used to quantitatively measure intracellular calcium concentrations. They are unique in that they are dual-wavelength dyes that exhibit two peak excitation wavelengths when either bound to or free of Ca2+. Researchers measure the shifts in either the optimum absorption or emission wavelength intensities of the ratiometric dye used to accurately measure intracellular Ca2+ concentrations.

Ratiometric dyes are preferred over single-wavelength dyes because they minimize the effects of uneven dye loading, poor dye retention, photobleaching, and variations in cell thickness.

Ratiometric calcium indicators have been successfully used to monitor calcium mobilization, image the spatial dynamics of calcium signaling, and in HTS cell-based pharmacological screening of agonist-stimulated and antagonist-inhibited signaling through GPCRs. Among ratiometric calcium indicators, Fura-2 and Indo-1 are the most widely used.