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. Author manuscript; available in PMC: 2010 Apr 14.
Published in final edited form as: Chem Soc Rev. 2006 Oct 23;36(2):348–357. doi: 10.1039/b512651g

Fig. 1.

Fig. 1

The use of fluorescent dyes to detect anion transport. (a) Pyranine/HPTS: Transport of X− out of the vesicle is accompanied by cotransport of H+ or exchange of OH−. Deprotonation of pyranine (pKa = 7.2) causes an increase in fluorescence when excitation and detection wavelengths are suitably adjusted. (b) Lucigenin: Fluorescence of Lucigenin is quenched by halides (X−), but not by oxoanions such as nitrate, sulfate or phosphate (Y−). The experiment can detect the cotransport of M+X− or exchange of X− and Y−. (c) Safranin O: Fluorescence of the lipophilic, cationic dye increases when it associates with a membrane. Anion transport into the vesicle generates a membrane potential difference (i.e. an electric field) that drives the dye into the membrane, thus increasing fluorescence.