Asymmetric Nafion-Coated Nanopore Electrode Arrays as Redox-Cycling-Based Electrochemical Diodes

Abstract

Inspired by the functioning of cellular ion channels, pore-based structures with nanoscale openings have been fabricated and integrated into ionic circuits, for example, ionic diodes and transistors, for signal processing and detection. In these systems, the nonlinear current responses arise either because asymmetric nanopore geometries break the symmetry of the ion distribution, creating unequal surface charge across the nanopore, or by coupling unidirectional electron transfer within a nanopore electrode. Here we develop a high-performance redox-cycling-based electrochemical diode by coating an asymmetric ion-exchange membrane, that is, Nafion, on the top surface of a nanopore electrode array (Nafion@NEA), in which each pore in the array exhibits one or more annular electrodes. Nafion@NEAs exhibit highly sensitive and charge-selective electroanalytical measurements due to efficient redox-cycling reaction, the permselectivity of Nafion, and the strong confinement of redox species in the nanopore array. In addition, the top electrode of dual-electrode Nafion@NEAs can serve as a voltage-controlled switch to gate ion transport within the nanopore. Thus Nafion@NEAs can be operated as a diode by switching voltages applied to the top and bottom electrodes of the NEA, leading to a large rectification ratio, fast response times, and simplified circuitry without the need for external electrodes. By taking advantage of closely spaced and individually addressable electrodes, the redox-cycling electrochemical diode has the potential for application to large-scale production and electrochemically controlled circuit operations, which go well beyond conventional electronic diodes or transistors.

Electrowetting‐Mediated Transport to Produce Electrochemical Transistor Action in Nanopore Electrode Arrays

“…cation-selective Nafion, on 2E-NEAs, results in electrochemical diode behavior. [26] In addition, encapsulating attoliter-volume NEAs with a polydimethylsiloxane membrane produces strong current rectification and up to 250-fold signal amplification, both of which are attributed to enhanced mass transport by meniscus evolution. [27] The versatile range of electrochemical and transport phenomena unearthed in dual-electrode NEAs suggests that even greater utility could be achieved by integrating a third electrode.…”

“…To fabricate the 3E-NEA, we followed previously developed methods from this laboratory based on a combination of nanosphere lithography (NSL) and reactive-ion etching (RIE). [26][27][28] Briefly, ≈70 nm each of gold, silicon nitride (SiN x ), gold, SiN x , gold, and lastly 200 nm of silicon dioxide (SiO 2 ) were serially deposited on a glass substrate by e-beam evaporation for Au and plasma-enhanced chemical vapor deposition for SiN x and SiO 2 . It should be noted that ≈±10 nm variation in the deposition thickness for nominal 70 nm SiN x dielectric layers was observed with scanning electron microscope (SEM) imaging for the different batch of device fabrication.…”

Enhanced Bipolar Electrochemistry at Solid-State Micropores: Demonstration by Wireless Electrochemiluminescence Imaging

“…Solid-state micropores are very attractive tools for a wide range of analytical applications including purification membranes and characterization of synthetic particles and bioentities such as cells and bacteria. − In contrast to biological micropores, solid-state micropores can withstand a wide variety of experimental conditions in terms of pH, salinity, and temperature . Micropores are used to detect and discriminate efficiently circulating tumor cells from other blood cells. , This discrimination is based on the variations of the electric signals (typically ionic currents) upon passage of cells presenting different physical properties (size, zeta potential, elasticity, viscosity, etc.).…”

Nanopore-Templated Silver Nanoparticle Arrays Photopolymerized in Zero-Mode Waveguides

“…Figure 1A illustrates the fabrication process using standard photolithography, layer-by-layer deposition, and FIB milling to produce nanopore recessed Ag ring electrode arrays. This simple direct-write approach enables direct fabrication of precise nanopore structures exhibiting conical frustum shapes in contrast to the cylindrical nanopores obtained using electron beam (Dawson et al, 2012; Kleijn et al, 2012) or nanosphere lithography (Fu et al, 2018). Cylindrical pore shapes would likely result in minor alterations to the concentration parameters required for optimal pore filling due to changing in polymer wetting behavior, and the extent to which the photocrosslinking radiation can penetrate the pore.…”