Combined use of two membrane-potential-sensitive dyes for determination of the Galvani potential difference across a biomimetic oil/water interface

The fluorescence behavior of anionic membrane-potential-sensitive dyes, bis -(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC 4 (3)) and bis -(1,3-diethylthiobarbituric acid)trimethine oxonol (DiSBAC 2 (3)), at a biomimetic 1,2-dichloroethane (DCE)/water (W) interface was studied by the mean of potential-modulated fluorescence (PMF) spectroscopy. The respective dyes gave a well-defined PMF signal due to the adsorption/desorption at the DCE/W interface. It was also found that the potentials where the two dyes gave the PMF signals were different by about 100 mV. We then attempted a combined use of the two dyes for determination of the Galvani potential difference across the DCE/W interface. When 40 μM DiBAC 4 (3) and 15 μM DiSBAC 2 (3) were initially added to the W phase, distinctly different spectra were obtained for different interfacial potentials. The ratio of the PMF signal intensities at 530 and 575 nm (the fluorescence maximum wavelengths for the respective dyes) showed a clear dependence on the interfacial potential. These results suggested the potential utility of the combined use of two dyes for the determination of membrane potentials in vivo. Figure Combined use of two membrane-potential-sensitive dyes that show different colors of fluorescence emission at their specific adsorption potentials.