What is a ratiometric indicator?

A ratiometric indicator is a type of dual-wavelength fluorescent dye that allows researchers to accurately measure intracellular calcium concentrations. Ratiometric indicators offer several advantages over single-wavelength indicators because of their unique spectral properties that deliver more robust and reproducible results. A ratiometric readout reduces the problems associated with dye leakage, photobleaching, uneven dye loading and measuring Ca2+ in cells of varying thicknesses.

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.