Di-8-ANEPPS is a potentiometric fluorescent dye that can be used to noninvasively measure transmembrane voltage. It is not fluorescent in water, but when bound to the lipid bilayer, becomes strongly fluorescent (ex/em max = ~467/631 nm). The fluorescence intensity of di-8-ANEPPS varies proportionally to changes in transmembrane voltage. This dye is most suitable for measuring larger changes in membrane voltage, such as the onset of induced membrane voltage in nonexcitable cells exposed to external electric fields or action potentials in excitable cells. Since di-8-ANEPPS stains the membrane, it can also be used simply as a cell membrane marker.
