Simultaneous Multipass Resistive-Pulse Sensing and Fluorescence Imaging of Liposomes.

Simultaneous multipass resistive-pulse sensing and fluorescence imaging have been used to correlate the size and fluorescence intensity of individual lipid liposomes composed of polar lipid extracts labeled with membrane-bound 3,3-dioctadecyloxacarbocyanine (DiO) fluorescent molecules. Here, a nanopipet serves as a waveguide to direct excitation light to the resistive-pulse sensing zone at the end of the nanopipet tip. Individual DiO-labeled liposomes (>50 nm radius) were multipassed back and forth through the orifices of glass nanopipets' 110-150 nm radius via potential switching to obtain subnanometer sizing precision, while recording the fluorescence intensity of the membrane-bound DiO molecules.

Single-Molecule Electrical Currents Associated with Valinomycin Transport of K.

A quantitative description of ionophore-mediated ion transport is important in understanding ionophore activity in biological systems and developing ionophore applications. Herein, we describe the direct measurement of the electrical current resulting from K transport mediated by valinomycin () ionophores. Step fluctuations in current measured across a 1,2-diphytanoyl--glycero-3-phosphocholine (DPhPC) bilayer suspended over a ∼400 nm radius glass nanopore result from dynamic partitioning of between the bilayer and torus region, effectively increasing or decreasing the total number of present in the membrane.