Anionic Conjugated Polyelectrolytes for FRET-based Imaging of Cellular Membrane Potential

Abstract

We report a Forster resonance energy transfer (FRET)-based imaging ensemble for the visualization of membrane potential in living cells. A water-soluble poly(fluorene-cophenylene) conjugated polyelectrolyte (FsPFc10) serves as a FRET donor to a voltage-sensitive dye acceptor (FluoVolt((TM))). We observe FRET between FsPFc10 and FluoVolt((TM)), where the enhancement in FRET-sensitized emission from FluoVolt((TM)) is measured at various donor/acceptor ratios. At a donor/acceptor ratio of 1, the excitation of FluoVolt((TM)) in a FRET configuration results in a three-fold enhancement in its fluorescence emission (compared to when it is excited directly). FsPFc10 efficiently labels the plasma membrane of HEK 293T/17 cells and remains resident with minimal cellular internalization for 1.5 h. The successful plasma membrane-associated colabeling of the cells with the FsPFc10-FluoVolt((TM)) donor-acceptor pair is confirmed by dual-channel confocal imaging. Importantly, cells labeled with FsPFc10 show excellent cellular viability with no adverse effect on cell membrane depolarization. During depolarization of membrane potential, HEK 293T/17 cells labeled with the donor-acceptor FRET pair exhibit a greater fluorescence response in FluoVolt((TM)) emission relative to when FluoVolt((TM)) is used as the sole imaging probe. These results demonstrate the conjugated polyelectrolyte to be a new class of membrane labeling fluorophore for use in voltage sensing schemes.