How does Fura red work?

Fura Red is a visible light-excitable analog of Fura-2 that can be used to ratiometrically measure Ca²⁺ in single cells. It's visible-light excitation (∼488 nm) and long-wavelength emission maxima (∼639 nm) minimizes background interference and enables multicolor analysis with green fluorescent probes. Chelation of Ca²⁺ by Fura Red results in a decrease of the fluorescence emission when excited at 488 nm. The fluorescent behavior of Fura red dyes is strongly dependent on certain environmental factors such as ionic strength, pH, pressure, and temperature. Fura Red is available as a membrane-permeant AM ester or a membrane-impermeant salt derivative.