On Developing Field-Effect-Tunable Nanofluidic Ion Diodes with Bipolar, Induced-Charge Electrokinetics

Abstract

We introduce herein the induced-charge electrokinetic phenomenon to nanometer fluidic systems; the design of the nanofluidic ion diode for field-effect ionic current control of the nanometer dimension is developed by enhancing internal ion concentration polarization through electrochemical transport of inhomogeneous inducing-counterions resulting from double gate terminals mounted on top of a thin dielectric layer, which covers the nanochannel connected to microfluidic reservoirs on both sides. A mathematical model based on the fully-coupled Poisson-Nernst-Plank-Navier-Stokes equations is developed to study the feasibility of this structural configuration causing effective ionic current rectification. The effect of various physiochemical and geometrical parameters, such as the native surface charge density on the nanochannel sidewalls, the number of gate electrodes (GE), the gate voltage magnitude, and the solution conductivity, permittivity, and thickness of the dielectric coating, as well as the size and position of the GE pair of opposite gate polarity, on the resulted rectification performance of the presented nanoscale ionic device is numerically analyzed by using a commercial software package, COMSOL Multiphysics (version 5.2). Three types of electrohydrodynamic flow, including electroosmosis of 1st kind, induced-charge electroosmosis, and electroosmosis of 2nd kind that were originated by the Coulomb force within three distinct charge layers coexist in the micro/nanofluidic hybrid network and are shown to simultaneously influence the output current flux in a complex manner. The rectification factor of a contrast between the ‘on’ and ‘off’ working states can even exceed one thousand-fold in the case of choosing a suitable combination of several key parameters. Our demonstration of field-effect-tunable nanofluidic ion diodes of double external gate electrodes proves invaluable for the construction of a flexible electrokinetic platform for ionic current control and may help transform the field of smart, on-chip, integrated circuits.

Multifrequency Induced-Charge Electroosmosis

“…Counterion screening inside the liquid phase enters into consideration, so to account for the Coulomb force within the IDL. Accordingly, the Ohm current from the bulk has to relay the displacement current flowing across the thin boundary layer, in terms of a current continuity on the surface of those metal strips [69,70,71,72] σbold-italicn⋅∇trueϕ˜1=jω1CD1+δ(trueϕ˜1−trueϕ˜1i) for the ith terminal in the TW field σbold-italicn⋅∇trueϕ˜2=jω2CD1+δ(trueϕ˜2−trueϕ˜2i) for the ith terminal in the SW field where σ is the liquid conductivity, trueϕ˜1/…”

Micro/Nano-Chip Electrokinetics, Volume III

“…Aiming to generate a gas-actuated microvalve, the authors have used an unfocused CO 2 laser beam to fabricate semi-circular fluid channels. Likewise, in another recent study [70], the whole-thermoplastic microfluidic functional elements, including a pneumatic (gas-actuated) normally closed microvalve, a micro-check valve, and a pneumatic dual-phase micropump have been fabricated for lab-on-a-chip applications [70]. Analytical microfluidics in the fields of protein, DNA, bacteria and virus and cells uses electrokinetics to sort, separate, concentrate and fix them for their analysis [71].…”

A Simulation Analysis of Nanofluidic Ion Current Rectification Using a Metal-Dielectric Janus Nanopore Driven by Induced-Charge Electrokinetic Phenomena

“…In the meantime, the Maxwell stress exerted on any electrical phase interface is not incorporated in the multiphysics numerical model, in that all the solid entities in the nanopore ion device are physically fastened on an insulating substrate. Since the electroosmotic pump flow rate along the ion-selective nanochannel is usually much larger than traditional electroosmosis in microchannels dictated by bulk conductivity, it is reasonable for us to disregard Debye screening on insulating charged walls of microchambers on both sides [75,76]. In spite of this, the extended space charge layer (ESCL) induced in IDZ can be still captured by our numerical simulation, since the physical origin is in regard to non-uniform surface conduction of excessive counterionic charges within the nanopore, rather than charging of microchannel walls, as has been explicitly considered in the mathematical treatment.…”