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

Abstract

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 individual valinomycin (val) ionophores.Step fluctuations in current measured across a 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) bilayer suspended over a ∼400 nm radius glass nanopore result from dynamic partitioning of val between the bilayer and torus region, effectively increasing or decreasing the total number of val present in the membrane. In our studies, approximately 30 val are present in the membrane on average with a val entering or leaving the bilayer approximately every 50 s, allowing measurement of changes in electrical current associated with individual val. The single-molecule val(K + ) transport current at 0.1 V applied potential is (1.3 ± 0.6) × 10 −15 A, consistent with estimates of the transport kinetics based on large val ensembles. This methodology for analyzing single ionophore transport is general and can be applied to other carrier-type ionophores.

Simultaneous Multipass Resistive-Pulse Sensing and Fluorescence Imaging of Liposomes

“…The radii of the liposome and PS were calculated using the resistive pulses associated with the particle entering the nanopipet. Use of eq assumes that the liposomes are spherical and that their lipid membrane presents an infinite resistance to ion fluxes . As shown in Figure S11, 90 nm radius PS nanoparticles produced an average blockage current of 1.52 ± 0.02% for a 111 ± 8 nm radius nanopipet orifice.…”

“…Use of eq 2 assumes that the liposomes are spherical and that their lipid membrane presents an infinite resistance to ion fluxes. 51 As shown in Figure S11, 90 nm radius PS nanoparticles produced an average blockage current of 1.52 ± 0.02% for a 111 ± 8 nm radius nanopipet orifice.…”

Large-Scale Wearable Textile-Based Sweat Sensor with High Sensitivity, Rapid Response, and Stable Electrochemical Performance

“…The ability of the TPFV/CPP yarn to analyze potassium ions as a K + -selective sensing yarn is attributed to the inclusion of valinomycin within the cortical fibers, which acts as a specialized carrier for K + . 55 Valinomycin is able to form a 1:1 complex with metal K + because the cavity size can accommodate only K + , enabling the TPFV/CPP yarn to capture and fix K + (Figure S11). Besides, the SC layer is an ion-electron converter that enhances the electron transfer capability.…”

Nanoelectrochemistry at liquid/liquid interfaces for analytical, biological, and material applications

“…150 This limitation was discussed in the recent study of K + transport by single valinomycin molecules through the bilayer lipid membrane. 151…”