AC Electrokinetics in Microfluidic Devices, Volume II

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "C:Chemistry".

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 7783

Special Issue Editors


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Guest Editor
Departamento de Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla, 41012 Seville, Spain
Interests: electrokinetics; dielectrophoresis; microfluidics; electrohydrodynamics
Special Issues, Collections and Topics in MDPI journals

E-Mail Website1 Website2
Guest Editor
Departamento de Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla, 41012 Seville, Spain
Interests: electrokinetics; microfluidics; dielectrophoresis; electrowetting
Special Issues, Collections and Topics in MDPI journals

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Guest Editor Assistant
School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK
Interests: microfluidics; electrokinetics; dielectrophoresis

Special Issue Information

Dear Colleagues,

Electric fields are commonly used for manipulating and characterizing liquids and small particles in suspension. Several applications in microsystems have appeared over the last few decades in diverse research fields, such as colloidal science, microelectronics, and biotechnology. For example, dielectrophoretic (DEP) forces can be used for manipulation and separation of a great variety of particles, such as biological cells, semiconductor nanowires or tiny metal colloids. DEP combined with electrokinetic-induced fluid flows can be leveraged for particle concentration in microfluidic devices. Additionally, particle–particle interactions (electric and/or hydrodynamic) arise upon application of electric fields, leading to self-assembly patterns, a common bottom-up approach for the fabrication of engineered microstructures. Several electric field-induced fluid flows occur in microelectrode structures; these flows can be used for standard liquid manipulation, such as pumping and mixing. In addition, the electrowetting effect allows for fine tuning of contact angle and droplet manipulation within microsystems. AC electrokinetics has also been used to characterize the dielectric properties of particles through DEP, as well as to assist other measurement techniques such as fluorescent spectroscopy or electrical impedance spectroscopy by pre-concentrating the particles.

This Special Issue seeks to showcase research papers, communications, and review articles that focus on all aspects of the application of AC electrokinetic methods in microfluidics and lab-on-a-chip technologies.

Prof. Dr. Antonio Ramos
Dr. Pablo García-Sánchez
Raúl Fernández-Mateo
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • dielectrophoresis
  • electrorotation
  • electrophoresis
  • electroosmosis
  • non-linear electrokinetics
  • electrowetting

Related Special Issue

Published Papers (7 papers)

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Research

22 pages, 7732 KiB  
Article
Trajectories and Forces in Four-Electrode Chambers Operated in Object-Shift, Dielectrophoresis and Field-Cage Modes—Considerations from the System’s Point of View
by Jan Gimsa and Michal M. Radai
Micromachines 2023, 14(11), 2042; https://doi.org/10.3390/mi14112042 - 31 Oct 2023
Viewed by 645
Abstract
In two previous papers, we calculated the dielectrophoresis (DEP) force and corresponding trajectories of high- and low-conductance 200-µm 2D spheres in a square 1 × 1-mm chamber with plane-versus-pointed, plane-versus-plane and pointed-versus-pointed electrode configurations by applying the law of maximum entropy production (LMEP) [...] Read more.
In two previous papers, we calculated the dielectrophoresis (DEP) force and corresponding trajectories of high- and low-conductance 200-µm 2D spheres in a square 1 × 1-mm chamber with plane-versus-pointed, plane-versus-plane and pointed-versus-pointed electrode configurations by applying the law of maximum entropy production (LMEP) to the system. Here, we complete these considerations for configurations with four-pointed electrodes centered on the chamber edges. The four electrodes were operated in either object-shift mode (two adjacent electrodes opposite the other two adjacent electrodes), DEP mode (one electrode versus the other three electrodes), or field-cage mode (two electrodes on opposite edges versus the two electrodes on the other two opposite edges). As in previous work, we have assumed DC properties for the object and the external media for simplicity. Nevertheless, every possible polarization ratio of the two media can be modeled this way. The trajectories of the spherical centers and the corresponding DEP forces were calculated from the gradients of the system’s total energy dissipation, described by numerically-derived conductance fields. In each of the three drive modes, very high attractive and repulsive forces were found in front of pointed electrodes for the high and low-conductance spheres, respectively. The conductance fields predict bifurcation points, watersheds, and trajectories with multiple endpoints. The high and low-conductance spheres usually follow similar trajectories, albeit with reversed orientations. In DEP drive mode, the four-point electrode chamber provides a similar area for DEP measurements as the classical plane-versus-pointed electrode chamber. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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16 pages, 3486 KiB  
Article
pH Gradients in Spatially Non-Uniform AC Electric Fields around the Charging Frequency; A Study of Two Different Geometries and Electrode Passivation
by Azade Tahmasebi, Sanaz Habibi, Jeana L. Collins, Ran An, Esmaeil Dehdashti and Adrienne Robyn Minerick
Micromachines 2023, 14(9), 1655; https://doi.org/10.3390/mi14091655 - 23 Aug 2023
Viewed by 904
Abstract
Dielectrophoresis (DEP), a precision nonlinear electrokinetic tool utilized within microfluidic devices, can induce bioparticle polarization that manifests as motion in the electric field; this phenomenon has been leveraged for phenotypic cellular and biomolecular detection, making DEP invaluable for diagnostic applications. As device operation [...] Read more.
Dielectrophoresis (DEP), a precision nonlinear electrokinetic tool utilized within microfluidic devices, can induce bioparticle polarization that manifests as motion in the electric field; this phenomenon has been leveraged for phenotypic cellular and biomolecular detection, making DEP invaluable for diagnostic applications. As device operation times lengthen, reproducibility and precision decrease, which has been postulated to be caused by ion gradients within the supporting electrolyte medium. This research focuses on characterizing pH gradients above, at, and below the electrode charging frequency (0.2–1.4 times charging frequency) in an aqueous electrolyte solution in order to extend the parameter space for which microdevice-imposed artifacts on cells in clinical diagnostic devices have been characterized. The nonlinear alternating current (AC) electric fields (0.07 Vpp/μm) required for DEP were generated via planar T-shaped and star-shaped microelectrodes overlaid by a 70 μm high microfluidic chamber. The experiments were designed to quantify pH changes temporally and spatially in the two microelectrode geometries. In parallel, a 50 nm hafnium oxide (HfO2) thin film on the microelectrodes was tested to provide insights into the role of Faradaic surface reactions on the pH. Electric field simulations were conducted to provide insights into the gradient shape within the microelectrode geometries. Frequency dependence was also examined to ascertain ion electromigration effects above, at, and below the electrode charging frequency. The results revealed Faradaic reactions above, at, and below the electrode charging frequency. Comparison experiments further demonstrated that pH changes caused by Faradaic reactions increased inversely with frequency and were more pronounced in the star-shaped geometry. Finally, HfO2 films demonstrated frequency-dependent properties, impeding Faradaic reactions. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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12 pages, 3539 KiB  
Article
Multiphase Actuation of AC Electrothermal Micropump
by Stirling Cenaiko, Thomas Lijnse and Colin Dalton
Micromachines 2023, 14(4), 758; https://doi.org/10.3390/mi14040758 - 29 Mar 2023
Cited by 1 | Viewed by 871
Abstract
Electrothermal micropumps apply an AC electric field to a conductive fluid within the range of 10 kHz–1 MHz to generate fluid flow. In this frequency range, coulombic forces dominate fluid interactions over opposing dielectric forces, resulting in high flow rates (~50–100 μm/s). To [...] Read more.
Electrothermal micropumps apply an AC electric field to a conductive fluid within the range of 10 kHz–1 MHz to generate fluid flow. In this frequency range, coulombic forces dominate fluid interactions over opposing dielectric forces, resulting in high flow rates (~50–100 μm/s). To date, the electrothermal effect—using asymmetrical electrodes—has been tested only with single-phase and 2-phase actuation, while dielectrophoretic micropumps have shown improved flow rates with 3- and 4-phase actuation. Simulating muti-phase signals in COMSOL Multiphysics requires additional modules and a more involved implementation to accurately represent the electrothermal effect in a micropump. Here, we report detailed simulations of the electrothermal effect under multi-phase conditions, including single-phase, 2-phase, 3-phase and 4-phase actuation patterns. These computational models indicate that 2-phase actuation leads to the highest flow rate, with 3-phase resulting in a 5% reduced flow rate and 4-phase resulting in an 11% reduced flow rate compared to 2-phase. With these modifications to the simulation, various actuation patterns can later be tested in COMSOL for a range of electrokinetic techniques. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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17 pages, 1806 KiB  
Article
Impedance-Frequency Response of Closed Electrolytic Cells
by José Juan López-García, José Horno and Constantino Grosse
Micromachines 2023, 14(2), 368; https://doi.org/10.3390/mi14020368 - 31 Jan 2023
Cited by 1 | Viewed by 843
Abstract
The electric AC response of electrolytic cells with DC bias is analyzed solving numerically the Poisson–Nernst–Planck equations and avoiding the commonly used infinite solution approximation. The results show the presence of an additional low-frequency dispersion process associated with the finite spacing of the [...] Read more.
The electric AC response of electrolytic cells with DC bias is analyzed solving numerically the Poisson–Nernst–Planck equations and avoiding the commonly used infinite solution approximation. The results show the presence of an additional low-frequency dispersion process associated with the finite spacing of the electrodes. Moreover, we find that the condition of fixed ionic content inside the electrolytic cell has a strong bearing on both the steady-state and the frequency response. For example: the characteristic frequency of the high-frequency dispersion decreases when the DC potential increases and/or the electrode spacing decreases in the closed cell case, while it remains essentially insensitive on these changes for open cells. Finally, approximate analytic expressions for the dependences of the main parameters of both dispersion processes are also presented. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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14 pages, 1773 KiB  
Article
Scattering of Metal Colloids by a Circular Post under Electric Fields
by José Eladio Flores-Mena, Pablo García-Sánchez and Antonio Ramos
Micromachines 2023, 14(1), 23; https://doi.org/10.3390/mi14010023 - 22 Dec 2022
Cited by 1 | Viewed by 1034
Abstract
We consider the scattering of metal colloids in aqueous solutions by an insulating circular post under the action of an AC electric field. We analyze the effects on the particle of several forces of electrical origin: the repulsion between the induced dipole of [...] Read more.
We consider the scattering of metal colloids in aqueous solutions by an insulating circular post under the action of an AC electric field. We analyze the effects on the particle of several forces of electrical origin: the repulsion between the induced dipole of the particle and its image dipole in the post, the hydrodynamic interaction with the post due to the induced-charge electroosmotic (ICEO) flow around the particle, and the dielectrophoresis arising from the distortion of the applied electric field around the post. The relative influence of these forces is discussed as a function of frequency of the AC field, particle size and distance to the post. We perform numerical simulations of the scattering of the metal colloid by the insulating circular post flowing in a microchannel and subjected to alternating current electric fields. Our simulation results show that the maximum particle deviation is found for an applied electric field parallel to the flow direction. The deviation is also greater at low electric field frequencies, corresponding to the regime in which the ICEO’s interaction with the post is predominant over other mechanisms. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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8 pages, 3079 KiB  
Article
Oscillatory Motion of Water Droplets Both in Oil and on Superhydrophobic Surface under Corona Discharge
by Qiang Tang, Zongtang Zhang, Jia-Han Zhang, Feiran Tang, Chengjun Wang and Xiaxia Cui
Micromachines 2022, 13(12), 2229; https://doi.org/10.3390/mi13122229 - 15 Dec 2022
Cited by 3 | Viewed by 1229
Abstract
Charged droplets driven by Coulomb force are an important part of a droplet-based micro reactor. In this study, we realized the rapid oscillatory motion of droplets both in oil and on superhydrophobic surface by injecting charges through corona discharge. Distinct from the oscillatory [...] Read more.
Charged droplets driven by Coulomb force are an important part of a droplet-based micro reactor. In this study, we realized the rapid oscillatory motion of droplets both in oil and on superhydrophobic surface by injecting charges through corona discharge. Distinct from the oscillatory motion of water droplets under a DC electric field, charge injection can make the motion of water droplets more flexible. A droplet in the oil layer can move up and down regularly under the action of corona discharge, and the discharge voltage can control the movement period and height of the droplet. In addition, the left–right translation of droplets on a superhydrophobic surface can be achieved by injecting charges into the hydrophobic film surface through corona discharge. Two kinds of droplet motion behaviors are systematically analyzed, and the mechanism of droplet motion is explained. The present results could help establish new approaches to designing efficient machines in microfluidics and micromechanical equipment. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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20 pages, 1045 KiB  
Article
Travelling-Wave Electrophoresis, Electro-Hydrodynamics, Electro-Rotation, and Symmetry-Breaking of a Polarizable Dimer in Non-Uniform Fields
by Touvia Miloh and Eldad J. Avital
Micromachines 2022, 13(8), 1173; https://doi.org/10.3390/mi13081173 - 25 Jul 2022
Cited by 1 | Viewed by 1178
Abstract
A theoretical framework is presented for calculating the polarization, electro-rotation, travelling-wave dielectrophoresis, electro-hydrodynamics and induced-charge electroosmotic flow fields around a freely suspended conducting dimer (two touching spheres) exposed to non-uniform direct current (DC) or alternating current (AC) electric fields. The analysis is based [...] Read more.
A theoretical framework is presented for calculating the polarization, electro-rotation, travelling-wave dielectrophoresis, electro-hydrodynamics and induced-charge electroosmotic flow fields around a freely suspended conducting dimer (two touching spheres) exposed to non-uniform direct current (DC) or alternating current (AC) electric fields. The analysis is based on employing the classical (linearized) Poisson–Nernst–Planck (PNP) formulation under the standard linearized ‘weak-field’ assumption and using the tangent-sphere coordinate system. Explicit expressions are first derived for the axisymmetric AC electric potential governed by the Robin (mixed) boundary condition applied on the dimer surface depending on the resistance–capacitance circuit (RC) forcing frequency. Dimer electro-rotation due to two orthogonal (out-of-phase) uniform AC fields and the corresponding mobility problem of a polarizable dimer exposed to a travelling-wave electric excitation are also analyzed. We present an explicit solution for the non-linear induced-charge electroosmotic (ICEO) flow problem of a free polarized dimer in terms of the corresponding Stokes stream function determined by the Helmholtz–Smoluchowski velocity slip. Next, we demonstrate how the same framework can be used to obtain an exact solution for the electro-hydrodynamic (EHD) problem of a polarizable sphere lying next to a conducting planar electrode. Finally, we present a new solution for the induced-charge mobility of a Janus dimer composed of two fused spherical colloids, one perfectly conducting and one dielectrically coated. So far, most of the available electrokinetic theoretical studies involving polarizable nano/micro shapes dealt with convex configurations (e.g., spheres, spheroids, ellipsoids) and as such the newly obtained electrostatic AC solution for a dimer provides a useful extension for similar concave colloids and engineered particles. Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices, Volume II)
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