Are there any red calcium flux dyes?

Yes, there are several red calcium flux dyes. One example is BioTracker NIR Ca2+ dyes, including SCT021, SCT022, and SCT023. These are fluorescent calcium indicators that emit light in the far-red spectrum. These dyes exhibit a substantial change in fluorescence intensity (up to a 1000-fold increase) upon binding to calcium ions within viable cells. The red calcium dye, ION Calcium Red-1 (ICR-1), is a fluorescent indicator which emits light in the red spectrum (Ex/Em: 580/660 nm) in response to changes in intracellular calcium levels. Its unique spectral properties enable the simultaneous use of another indicator of a different color or the observation of cells expressing GFP tags. Another example is Fura Red, which is a fluorescent dye that is sensitive to changes in calcium concentration. Its fluorescence decreases as the concentration of calcium ions increases. When Fura Red binds to calcium, it becomes a fluorescent compound that can be excited at 435 nm, emitting light at a peak wavelength of 639 nm.