Electric Field Modulation of the Membrane Potential in Solid-State Ion Channels Weihua Guan † and Mark A. Reed* ,†,‡ † Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520, United States ‡ Department of Applied Physics, Yale University, New Haven, Connecticut 06520, United States *S Supporting Information ABSTRACT: Biological ion channels are molecular devices that allow a rapid flow of ions across the cell membrane. Normal physiological functions, such as generating action potentials for cell-to-cell communication, are highly dependent on ion channels that can open and close in response to external stimuli for regulating ion permeation. Mimicking these biological functions using synthetic structures is a rapidly progressing yet challenging area. Here we report the electric field modulation of the membrane potential phenomena in mechanically and chemically robust solid-state ion channels, an abiotic analogue to the voltage-gated ion channels in living systems. To understand the complex physicochemical processes in the electric field regulated membrane potential behavior, both quasi-static and transient characteristics of converting transmembrane ion gradients into electric potential are investigated. It is found that the transmembrane potential can be adequately tuned by an external electrical stimulation, thanks to the unique properties of the voltage-regulated selective ion transport through a nanoscale channel. KEYWORDS: Nanochannel, membrane potential, electrofluidic gating, ion transport, salinity gradient power C onstruction of protocells (artificial cells with a minimum set of components to reproduce one or several cell functions) provides a novel platform to understand the complex biological-physical-chemical processes in a living biological cell. The most indispensable components in constructing protocells are the cell membranes in which ion channels are embedded to facilitate chemical and electrical communication with the extracellular environment. Most of the work so far has used soft materials such as phospholipids and polymersomes to implement the ion channel elements. 1,2 Although these soft materials are native relatives to living cell membranes and have proved to be very useful for a range of interesting experiments, 1 they exhibit a number of disadvan- tages such as limited stability under various pH, salt concentration, temperature, and mechanical stress conditions. Fabrication of the membranes from solid-state materials presents obvious advantages over their soft matter counterparts, such as very high stability, adjustable surface properties, and the potential for integration into devices and networks. Indeed, development of mechanically and chemically robust solid-state nanopores 2 and nanochannels 3 has already been a rapidly growing area of research due to various practical applications, such as single molecule sensors, 4 energy conversion, 5 and desalination. 6 One of the most important characteristics in biological ion channels is its selectivity, which allows only specific kind of ions to pass through. The mechanism by which many biological channels achieve selectivity is on the molecular level. For example, in voltage-gated ion channels, 7 a conformational change will be initiated when the proteins bearing charged amino acids inside the ion channel relocates upon changes in the transmembrane electric field. Direct implementing physical conformational variation in solid-state platforms is a daunting task. 8 Instead, the electrostatic interactions, described by Poisson-Nernst-Planck equations, 9-11 are widely used to achieve the charge selectivity in solid-state structures. 12,13 Inspired by the action potential generation behavior in voltage-gated ion channels, we here propose and demonstrate a solid-state protocell built from top-down fabricated artificial solid-state ion channels (ASIC), whose membrane potential can be modulated by an orthogonal electric field. Previous experimental studies in solid-state nanochannels have consid- ered almost exclusively the voltage-driven phenomena, that is, the passage of ions through the nanochannels upon a potential gradient (i.e., the current-voltage relationship 1,2,12,14 ). The membrane potential phenomenon, essentially an open circuit and concentration-driven process, has been barely investigated in artificial ion channel systems. 5,15,16 This study adds another dimension to the unique properties of the regulated selective ion transport through a nanoscale channel. Device Structures. The protocell we envision to reproduce the membrane potential phenomena in biological cells (Figure 1a) is schematically shown in Figure 1b. It is a three-terminal device that is similar to a nanofluidic field effect transistor Received: October 15, 2012 Revised: November 8, 2012 Published: November 19, 2012 Letter pubs.acs.org/NanoLett © 2012 American Chemical Society 6441 dx.doi.org/10.1021/nl303820a | Nano Lett. 2012, 12, 6441-6447