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Editorial for the Special Issue on Micromachines for Dielectrophoresis, Volume II

by Rodrigo Martinez-Duarte

Micromachines 2023, 14(4), 769; https://doi.org/10.3390/mi14040769 - 30 Mar 2023

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Abstract

Dielectrophoresis (DEP) remains an effective technique for the label-free identification and manipulation of targeted particles ranging from sizes from nano to micrometers and from inert particles to biomolecules and cells [...] Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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18 pages, 12715 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Dielectrophoresis from the System’s Point of View: A Tale of Inhomogeneous Object Polarization, Mirror Charges, High Repelling and Snap-to-Surface Forces and Complex Trajectories Featuring Bifurcation Points and Watersheds

by Jan Gimsa and Michal M. Radai

Micromachines 2022, 13(7), 1002; https://doi.org/10.3390/mi13071002 - 26 Jun 2022

Cited by 3 | Viewed by 2048

Abstract

Microscopic objects change the apparent permittivity and conductivity of aqueous systems and thus their overall polarizability. In inhomogeneous fields, dielectrophoresis (DEP) increases the overall polarizability of the system by moving more highly polarizable objects or media to locations with a higher field. The [...] Read more.

Microscopic objects change the apparent permittivity and conductivity of aqueous systems and thus their overall polarizability. In inhomogeneous fields, dielectrophoresis (DEP) increases the overall polarizability of the system by moving more highly polarizable objects or media to locations with a higher field. The DEP force is usually calculated from the object’s point of view using the interaction of the object’s induced dipole or multipole moments with the inducing field. Recently, we were able to derive the DEP force from the work required to charge suspension volumes with a single object moving in an inhomogeneous field. The capacitance of the volumes was described using Maxwell–Wagner’s mixing equation. Here, we generalize this system’s-point-of-view approach describing the overall polarizability of the whole DEP system as a function of the position of the object with a numerical “conductance field”. As an example, we consider high- and low conductive 200 µm 2D spheres in a square 1 × 1 mm chamber with plain-versus-pointed electrode configuration. For given starting points, the trajectories of the sphere and the corresponding DEP forces were calculated from the conductance gradients. The model describes watersheds; saddle points; attractive and repulsive forces in front of the pointed electrode, increased by factors >600 compared to forces in the chamber volume where the classical dipole approach remains applicable; and DEP motions with and against the field gradient under “positive DEP” conditions. We believe that our approach can explain experimental findings such as the accumulation of viruses and proteins, where the dipole approach cannot account for sufficiently high holding forces to defeat Brownian motion. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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14 pages, 4611 KiB

Open AccessArticle

Sub–100 nm Nanoparticle Upconcentration in Flow by Dielectrophoretic Forces

by Maria Dimaki, Mark Holm Olsen, Noemi Rozlosnik and Winnie E. Svendsen

Micromachines 2022, 13(6), 866; https://doi.org/10.3390/mi13060866 - 30 May 2022

Cited by 6 | Viewed by 1863

Abstract

This paper presents a novel microfluidic chip for upconcentration of sub–100 nm nanoparticles in a flow using electrical forces generated by a DC or AC field. Two electrode designs were optimized using COMSOL Multiphysics and tested using particles with sizes as low as [...] Read more.

This paper presents a novel microfluidic chip for upconcentration of sub–100 nm nanoparticles in a flow using electrical forces generated by a DC or AC field. Two electrode designs were optimized using COMSOL Multiphysics and tested using particles with sizes as low as 47 nm. We show how inclined electrodes with a zig-zag three-tooth configuration in a channel of 20 µm width are the ones generating the highest gradient and therefore the largest force. The design, based on AC dielectrophoresis, was shown to upconcentrate sub–100 nm particles by a factor of 11 using a flow rate of 2–25 µL/h. We present theoretical and experimental results and discuss how the chip design can easily be massively parallelized in order to increase throughput by a factor of at least 1250. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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10 pages, 2508 KiB

Open AccessArticle

Particle-Induced Electrostatic Repulsion within an Electric Curtain Operating below the Paschen Limit

by Stuart J. Williams, Joseph D. Schneider, Benjamin C. King and Nicolas G. Green

Micromachines 2022, 13(2), 288; https://doi.org/10.3390/mi13020288 - 11 Feb 2022

Cited by 4 | Viewed by 2793

Abstract

The electric curtain is a platform developed to lift and transport charged particles in air. Its premise is the manipulation of charged particles; however, fewer investigations isolate dielectric forces that are observed at lower voltages (i.e., less than the Paschen limit). This work [...] Read more.

The electric curtain is a platform developed to lift and transport charged particles in air. Its premise is the manipulation of charged particles; however, fewer investigations isolate dielectric forces that are observed at lower voltages (i.e., less than the Paschen limit). This work focuses on observations of simultaneous dielectrophoretic and electrostatic forces. The electric curtain was a printed circuit board with interdigitated electrodes (0.020 inch width and spacing) coated with a layer of polypropylene, where a standing wave or travelling wave AC signal was applied (50 Hz) to produce an electric field below the Paschen limit. Soda lime glass beads (180–212 µm) demonstrated oscillatory rolling via dielectrophoretic forces. In addition, several particles simultaneously experienced rapid projectile repulsion, a behavior consistent with electrostatic phenomena. This second result is discussed as a particle-induced local increase in the electric field, with simulations demonstrating that a particle in close proximity to the curtain’s surface produces a local field enhancement of over 2.5 times. The significance of this is that individual particles themselves can trigger electrostatic repulsion in an otherwise dielectric system. These results could be used for advanced applications where particles themselves provided triggered responses, perhaps for selective sorting of micrometer particles in air. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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32 pages, 3763 KiB

Open AccessArticle

Protein Dielectrophoresis: A Tale of Two Clausius-Mossottis—Or Something Else?

by Ronald Pethig

Micromachines 2022, 13(2), 261; https://doi.org/10.3390/mi13020261 - 6 Feb 2022

Cited by 15 | Viewed by 2811

Abstract

Standard DEP theory, based on the Clausius–Mossotti (CM) factor derived from solving the boundary-value problem of macroscopic electrostatics, fails to describe the dielectrophoresis (DEP) data obtained for 22 different globular proteins over the past three decades. The calculated DEP force appears far too [...] Read more.

Standard DEP theory, based on the Clausius–Mossotti (CM) factor derived from solving the boundary-value problem of macroscopic electrostatics, fails to describe the dielectrophoresis (DEP) data obtained for 22 different globular proteins over the past three decades. The calculated DEP force appears far too small to overcome the dispersive forces associated with Brownian motion. An empirical theory, employing the equivalent of a molecular version of the macroscopic CM-factor, predicts a protein’s DEP response from the magnitude of the dielectric β-dispersion produced by its relaxing permanent dipole moment. A new theory, supported by molecular dynamics simulations, replaces the macroscopic boundary-value problem with calculation of the cross-correlation between the protein and water dipoles of its hydration shell. The empirical and formal theory predicts a positive DEP response for protein molecules up to MHz frequencies, a result consistently reported by electrode-based (eDEP) experiments. However, insulator-based (iDEP) experiments have reported negative DEP responses. This could result from crystallization or aggregation of the proteins (for which standard DEP theory predicts negative DEP) or the dominating influences of electrothermal and other electrokinetic (some non-linear) forces now being considered in iDEP theory. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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14 pages, 5126 KiB

Open AccessArticle

Modeling Brownian Microparticle Trajectories in Lab-on-a-Chip Devices with Time Varying Dielectrophoretic or Optical Forces

by Mohammad Asif Zaman, Mo Wu, Punnag Padhy, Michael A. Jensen, Lambertus Hesselink and Ronald W. Davis

Micromachines 2021, 12(10), 1265; https://doi.org/10.3390/mi12101265 - 18 Oct 2021

Cited by 11 | Viewed by 2860

Abstract

Lab-on-a-chip (LOC) devices capable of manipulating micro/nano-sized samples have spurred advances in biotechnology and chemistry. Designing and analyzing new and more advanced LOCs require accurate modeling and simulation of sample/particle dynamics inside such devices. In this work, we present a generalized computational physics [...] Read more.

Lab-on-a-chip (LOC) devices capable of manipulating micro/nano-sized samples have spurred advances in biotechnology and chemistry. Designing and analyzing new and more advanced LOCs require accurate modeling and simulation of sample/particle dynamics inside such devices. In this work, we present a generalized computational physics model to simulate particle/sample trajectories under the influence of dielectrophoretic or optical forces inside LOC devices. The model takes into account time varying applied forces, Brownian motion, fluid flow, collision mechanics, and hindered diffusion caused by hydrodynamic interactions. We develop a numerical solver incorporating the aforementioned physics and use it to simulate two example cases: first, an optical trapping experiment, and second, a dielectrophoretic cell sorter device. In both cases, the numerical results are found to be consistent with experimental observations, thus proving the generality of the model. The numerical solver can simulate time evolution of the positions and velocities of an arbitrarily large number of particles simultaneously. This allows us to characterize and optimize a wide range of LOCs. The developed numerical solver is made freely available through a GitHub repository so that researchers can use it to develop and simulate new designs. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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15 pages, 13762 KiB

Open AccessArticle

Dielectrophoretic Micro-Organization of Chondrocytes to Regenerate Mechanically Anisotropic Cartilaginous Tissue

by Yoshitaka Takeuchi and Shogo Miyata

Micromachines 2021, 12(9), 1098; https://doi.org/10.3390/mi12091098 - 11 Sep 2021

Cited by 4 | Viewed by 2377

Abstract

Recently, many studies have focused on the repair and regeneration of damaged articular cartilage using tissue engineering. In tissue engineering therapy, cells are cultured in vitro to create a three-dimensional (3-D) tissue designed to replace the damaged cartilage. Although tissue engineering is a [...] Read more.

Recently, many studies have focused on the repair and regeneration of damaged articular cartilage using tissue engineering. In tissue engineering therapy, cells are cultured in vitro to create a three-dimensional (3-D) tissue designed to replace the damaged cartilage. Although tissue engineering is a useful approach to regenerating cartilage, mechanical anisotropy has not been reconstructed from a cellular organization level. This study aims to create mechanically anisotropic cartilaginous tissue using dielectrophoretic cell patterning and gel-sheet lamination. Bovine chondrocytes were patterned in a hydrogel to form line-array cell clusters via negative dielectrophoresis (DEP). The results indicate that the embedded chondrocytes remained viable and reconstructed cartilaginous tissue along the patterned cell array. Moreover, the agarose gel, in which chondrocytes were patterned, demonstrated mechanical anisotropy. In summary, our DEP cell patterning and gel-sheet lamination techniques would be useful for reconstructing mechanically anisotropic cartilage tissues. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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18 pages, 1952 KiB

Open AccessArticle

Active, Reactive, and Apparent Power in Dielectrophoresis: Force Corrections from the Capacitive Charging Work on Suspensions Described by Maxwell-Wagner’s Mixing Equation

by Jan Gimsa

Micromachines 2021, 12(7), 738; https://doi.org/10.3390/mi12070738 - 23 Jun 2021

Cited by 7 | Viewed by 2324

Abstract

A new expression for the dielectrophoresis (DEP) force is derived from the electrical work in a charge-cycle model that allows the field-free transition of a single object between the centers of two adjacent cubic volumes in an inhomogeneous field. The charging work for [...] Read more.

A new expression for the dielectrophoresis (DEP) force is derived from the electrical work in a charge-cycle model that allows the field-free transition of a single object between the centers of two adjacent cubic volumes in an inhomogeneous field. The charging work for the capacities of the volumes is calculated in the absence and in the presence of the object using the external permittivity and Maxwell-Wagner’s mixing equation, respectively. The model provides additional terms for the Clausius-Mossotti factor, which vanish for the mathematical boundary transition toward zero volume fraction, but which can be interesting for narrow microfluidic systems. The comparison with the classical solution provides a new perspective on the notorious problem of electrostatic modeling of AC electrokinetic effects in lossy media and gives insight into the relationships between active, reactive, and apparent power in DEP force generation. DEP moves more highly polarizable media to locations with a higher field, making a DEP-related increase in the overall polarizability of suspensions intuitive. Calculations of the passage of single objects through a chain of cubic volumes show increased overall effective polarizability in the system for both positive and negative DEP. Therefore, it is proposed that DEP be considered a conditioned polarization mechanism, even if it is slow with respect to the field oscillation. The DEP-induced changes in permittivity and conductivity describe the increase in the overall energy dissipation in the DEP systems consistent with the law of maximum entropy production. Thermodynamics can help explain DEP accumulation of small objects below the limits of Brownian motion. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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12 pages, 2725 KiB

Open AccessArticle

A Study of Dielectrophoresis-Based Liquid Metal Droplet Control Microfluidic Device

by Lu Tian, Zi Ye and Lin Gui

Micromachines 2021, 12(3), 340; https://doi.org/10.3390/mi12030340 - 23 Mar 2021

Cited by 7 | Viewed by 2723

Abstract

This study presents a dielectrophoresis-based liquid metal (LM) droplet control microfluidic device. Six square liquid metal electrodes are fabricated beneath an LM droplet manipulation pool. By applying different voltages on the different electrodes, a non-uniform electric field is formed around the LM droplet, [...] Read more.

This study presents a dielectrophoresis-based liquid metal (LM) droplet control microfluidic device. Six square liquid metal electrodes are fabricated beneath an LM droplet manipulation pool. By applying different voltages on the different electrodes, a non-uniform electric field is formed around the LM droplet, and charges are induced on the surface of the droplet accordingly, so that the droplet could be driven inside the electric field. With a voltage of ±1000 V applied on the electrodes, the LM droplets are driven with a velocity of 0.5 mm/s for the 2.0 mm diameter ones and 1.0 mm/s for the 1.0 mm diameter ones. The whole chip is made of PDMS, and microchannels are fabricated by laser ablation. In this device, the electrodes are not in direct contact with the working droplets; a thin PDMS film stays between the electrodes and the driven droplets, preventing Joule heat or bubble formation during the experiments. To enhance the flexibility of the chip design, a gallium-based alloy with melting point of 10.6 °C is used as electrode material in this device. This dielectrophoresis (DEP) device was able to successfully drive liquid metal droplets and is expected to be a flexible approach for liquid metal droplet control. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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19 pages, 5499 KiB

Open AccessArticle

Characterization and Separation of Live and Dead Yeast Cells Using CMOS-Based DEP Microfluidics

by Honeyeh Matbaechi Ettehad and Christian Wenger

Micromachines 2021, 12(3), 270; https://doi.org/10.3390/mi12030270 - 6 Mar 2021

Cited by 17 | Viewed by 3723

Abstract

This study aims at developing a miniaturized CMOS integrated silicon-based microfluidic system, compatible with a standard CMOS process, to enable the characterization, and separation of live and dead yeast cells (as model bio-particle organisms) in a cell mixture using the DEP technique. DEP [...] Read more.

This study aims at developing a miniaturized CMOS integrated silicon-based microfluidic system, compatible with a standard CMOS process, to enable the characterization, and separation of live and dead yeast cells (as model bio-particle organisms) in a cell mixture using the DEP technique. DEP offers excellent benefits in terms of cost, operational power, and especially easy electrode integration with the CMOS architecture, and requiring label-free sample preparation. This can increase the likeliness of using DEP in practical settings. In this work the DEP force was generated using an interdigitated electrode arrays (IDEs) placed on the bottom of a CMOS-based silicon microfluidic channel. This system was primarily used for the immobilization of yeast cells using DEP. This study validated the system for cell separation applications based on the distinct responses of live and dead cells and their surrounding media. The findings confirmed the device’s capability for efficient, rapid and selective cell separation. The viability of this CMOS embedded microfluidic for dielectrophoretic cell manipulation applications and compatibility of the dielectrophoretic structure with CMOS production line and electronics, enabling its future commercially mass production. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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10 pages, 3062 KiB

Open AccessArticle

Design of Driving Waveform Based on a Damping Oscillation for Optimizing Red Saturation in Three-Color Electrophoretic Displays

by Zichuan Yi, Weibo Zeng, Simin Ma, Haoqiang Feng, Wenjun Zeng, Shitao Shen, Lingling Shui, Guofu Zhou and Chongfu Zhang

Micromachines 2021, 12(2), 162; https://doi.org/10.3390/mi12020162 - 7 Feb 2021

Cited by 24 | Viewed by 3102

Abstract

At present, three-color electrophoretic displays (EPDs) have problems of dim brightness and insufficient color saturation. In this paper, a driving waveform based on a damping oscillation was proposed to optimize the red saturation in three-color EPDs. The optimized driving waveform was composed of [...] Read more.

At present, three-color electrophoretic displays (EPDs) have problems of dim brightness and insufficient color saturation. In this paper, a driving waveform based on a damping oscillation was proposed to optimize the red saturation in three-color EPDs. The optimized driving waveform was composed of an erasing stage, a particles activation stage, a red electrophoretic particles purification stage, and a red display stage. The driving duration was set to 360 ms, 880 ms, 400 ms, and 2400 ms, respectively. The erasing stage was used to erase the current pixel state and refresh to a black state. The particles’ activation stage was set as two cycles, and then refreshed to the black state. The red electrophoretic particles’ purification stage was a damping oscillation driving waveform. The red and black electrophoretic particles were separated by changing the magnitude and polarity of applied electric filed, so that the red electrophoretic particles were purified. The red display stage was a low positive voltage, and red electrophoretic particles were driven to the common electrode to display a red state. The experimental results showed that the maximum red saturation could reach 0.583, which was increased by 27.57% compared with the traditional driving waveform. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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13 pages, 5302 KiB

Open AccessArticle

One-Dimensional Flow of Bacteria on an Electrode Rail by Dielectrophoresis: Toward Single-Cell-Based Analysis

by Yukihiro Yamaguchi and Takatoki Yamamoto

Micromachines 2021, 12(2), 123; https://doi.org/10.3390/mi12020123 - 24 Jan 2021

Cited by 4 | Viewed by 2877

Abstract

Many applications in biotechnology and medicine, among other disciplines, require the rapid enumeration of bacteria, preferably using miniaturized portable devices. Microfluidic technology is expected to solve this miniaturization issue. In the enumeration of bacteria in microfluidic devices, the technique of aligning bacteria in [...] Read more.

Many applications in biotechnology and medicine, among other disciplines, require the rapid enumeration of bacteria, preferably using miniaturized portable devices. Microfluidic technology is expected to solve this miniaturization issue. In the enumeration of bacteria in microfluidic devices, the technique of aligning bacteria in a single line prior to counting is the key to an accurate count at single-bacterium resolution. Here, we describe the numerical and experimental evaluation of a device utilizing a dielectrophoretic force to array bacteria in a single line, allowing their facile numeration. The device comprises a channel to flow bacteria, two counter electrodes, and a capture electrode several microns or less in width for arranging bacteria in a single line. When the capture electrode is narrower than the diameter of a bacterium, the entrapment efficiency of the one-dimensional array is 80% or more within 2 s. Furthermore, since some cell-sorting applications require bacteria to move against the liquid flow, we demonstrated that bacteria can move in a single line in the off-axial direction tilted 30° from the flow direction. Our findings provide the basis for designing miniature, portable devices for evaluating bacteria with single-cell accuracy. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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29 pages, 2081 KiB

Open AccessArticle

Travelling-Wave Dipolophoresis: Levitation and Electrorotation of Janus Nanoparticles

by Touvia Miloh and Jacob Nagler

Micromachines 2021, 12(2), 114; https://doi.org/10.3390/mi12020114 - 22 Jan 2021

Cited by 5 | Viewed by 2070

Abstract

We present a theoretical study of the hydrodynamic and electrokinetic response of both metallic spherical polarized colloids as well as metallodielectic Janus particles, which are subjected to an arbitrary non-uniform ambient electric field (DC or AC forcing). The analysis is based on employing [...] Read more.

We present a theoretical study of the hydrodynamic and electrokinetic response of both metallic spherical polarized colloids as well as metallodielectic Janus particles, which are subjected to an arbitrary non-uniform ambient electric field (DC or AC forcing). The analysis is based on employing the linearized ‘standard’ model (Poisson–Nernst–Planck formulation) and on the assumptions of a ‘weak’ field and small Debye scale. In particular, we consider cases of linear and helical time-harmonic travelling-wave excitations and provide explicit expressions for the resulting dielectrophoretic and induced-charge electrophoretic forces and moments, exerted on freely suspended particles. The new analytic expressions thus derived for the linear and angular velocities of the initially uncharged polarizable particle are compared against some available solutions. We also analyze the levitation problem (including stability) of metallic and Janus particles placed in a cylindrical (insulating or conducting) pore near a powered electrode. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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12 pages, 3123 KiB

Open AccessArticle

Dielectrophoresis-Based Positioning of Carbon Nanotubes for Wafer-Scale Fabrication of Carbon Nanotube Devices

by Joevonte Kimbrough, Lauren Williams, Qunying Yuan and Zhigang Xiao

Micromachines 2021, 12(1), 12; https://doi.org/10.3390/mi12010012 - 25 Dec 2020

Cited by 12 | Viewed by 3183

Abstract

In this paper, we report the wafer-scale fabrication of carbon nanotube field-effect transistors (CNTFETs) with the dielectrophoresis (DEP) method. Semiconducting carbon nanotubes (CNTs) were positioned as the active channel material in the fabrication of carbon nanotube field-effect transistors (CNTFETs) with dielectrophoresis (DEP). The [...] Read more.

In this paper, we report the wafer-scale fabrication of carbon nanotube field-effect transistors (CNTFETs) with the dielectrophoresis (DEP) method. Semiconducting carbon nanotubes (CNTs) were positioned as the active channel material in the fabrication of carbon nanotube field-effect transistors (CNTFETs) with dielectrophoresis (DEP). The drain-source current (I_DS) was measured as a function of the drain-source voltage (V_DS) and gate-source voltage (V_GS) from each CNTFET on the fabricated wafer. The I_DS on/off ratio was derived for each CNTFET. It was found that 87% of the fabricated CNTFETs was functional, and that among the functional CNTFETs, 30% of the CNTFETs had an I_DS on/off ratio larger than 20 while 70% of the CNTFETs had an I_DS on/off ratio lower than 20. The highest I_DS on/off ratio was about 490. The DEP-based positioning of carbon nanotubes is simple and effective, and the DEP-based device fabrication steps are compatible with Si technology processes and could lead to the wafer-scale fabrication of CNT electronic devices. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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