What is a dual excitation dye?

A dual excitation dye is one in which the wavelength at which it is excited changes. Fura-2 is the most popular dual excitation dye.

Dual excitation dyes are also known as ratiometric dyes. The biggest advantage they offer over single excitation dyes is their ability to extract accurate quantitative data about intracellular ion concentrations. This is because dual excitation dyes have unique spectral properties that help minimize the problems caused by photobleaching, poor dye retention, variations in cell thicknesses, and uneven dye loading. Among ratiometric calcium indicators, Fura-2 and Indo-1 are the most widely used.