Chloride (Cl-) ion fluxes play an important role in cellular regulatory, absorptive, and secretory processes. The known Cl- indicators work by collisional quenching of fluorescence, an entirely different mechanism than that for the cation indicators. Quenching is not accompanied by spectral shift, so ratio measurements are not possible. Current Cl- indicators are based on the 6-methoxyquinoline fluorophore.
TEFLabs offers two Cl- indicators, SPQ (Figure 7.6) and MQAE (Figure 7.7).
Figure 7.6 SPQ
Figure 7.7 MQAE