Abstract
Abstract A report is given on the use of potential-sensitive dyes (PSDs) for monitoring the potential created at the membrane-sample interface due to the transport of ions from the (aqueous) sample into the lipid membrane by a neutral ion carrier. In a typical experiment, valinomycin carries potassium ion into the interior of a plasticized PVC membrane, and the PSD (a lipophilic cationic polymethine dye) detects the potential by undergoing a change in fluorescence emission intensity. Unlike in previous sensors based on the use of PSDs, the dye is used as an ion pair with a lipophilic anion. Several mechanisms are discussed that are likely to contribute to the observed change in fluorescence. These include electronic redistribution within the dye, spatial redistribution or voltage-dependent partitioning. In related experiments, changes in fluorescnce polarization have also been observed. Unlike many other kinds of ion optodes, the work function is virtually independent of pH. We finally discuss the microstructures of the membrane, the function of the PSD and the effects of additives.
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