Rhod-2, with fluorescence excitation maxima at 552 nm and emission maxima at 581 nm, was first introduced in 1989. Rhod-2 is essentially non-fluorescent before Ca2+ binding, becoming more fluorescent with increasing Ca2+ concentration. The longer excitations and emissions of Rhod-2 make the indicator useful for experiments in cells and tissues that have high levels of autofluorescence and for multiplexing with other fluorescent dyes of shorter wavelengths. The AM ester forms of these rhodamine-based indicators are cationic, which can result in potential-driven uptake into mitochondria.
Rhod-2 is also available in a Low Affinity version (Rhod-2 LowAFF).
For a longerwavelength calcium indicator with a truly red emission try TEFLabs new Asante Calcium Red
Excitation: 550 nm
Emission: 578 nm
kd: 570 nM
Solubility: H20 (salt form) DMSO (AM form)
Molecular Weight: 869 g/mol (salt form) 1124 g/mol (AM form)
Asante Calcium Red(ACR)
Asante Calcium Green(ACG)