Micromachines

Research

Jump to: Review

19 pages, 4925 KiB

Open AccessArticle

A Focus on Two Electrokinetics Issues

by Cheng Dai and Ping Sheng

Micromachines 2020, 11(12), 1028; https://doi.org/10.3390/mi11121028 - 24 Nov 2020

Viewed by 1621

Abstract

This review article intends to communicate the new understanding and viewpoints on two fundamental electrokinetics topics that have only become available recently. The first is on the holistic approach to the Poisson–Boltzmann equation that can account for the effects arising from the interaction [...] Read more.

This review article intends to communicate the new understanding and viewpoints on two fundamental electrokinetics topics that have only become available recently. The first is on the holistic approach to the Poisson–Boltzmann equation that can account for the effects arising from the interaction between the mobile ions in the Debye layer and the surface charge. The second is on the physical picture of the inner electro-hydrodynamic flow field of an electrophoretic particle and its drag coefficient. For the first issue, the traditional Poisson–Boltzmann equation focuses only on the mobile ions in the Debye layer; effects such as charge regulation and the isoelectronic point arising from the interaction between the mobile ions in the Debye layer and the surface charge are left to supplemental measures. However, a holistic treatment is entirely possible in which the whole electrical double layer—the Debye layer and the surface charge—is treated consistently from the beginning. While the derived form of the Poisson–Boltzmann equation remains unchanged, the zeta potential boundary condition becomes a calculated quantity that can reflect the various effects due to the interaction between the surface charges and the mobile ions in the liquid. The second issue, regarding the drag coefficient of a spherical electrophoretic particle, has existed ever since the breakthrough by Smoluchowski a century ago that linked the zeta potential of the particle to its mobility. Due to the highly nonlinear mathematics involved in the electro-hydrodynamics inside the Debye layer, there has been a lack of an exact solution for the electrophoretic flow field. Recent numerical simulation results show that the flow field comprises an inner region and an outer region, separated by a rather sharp interface. As the inner flow field is carried along by the particle, the measured drag is that at the inner/outer interface rather than at the solid/liquid interface. This identification and its associated physical picture of the inner flow field resolves a long-standing puzzle regarding the electrophoretic drag coefficient. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Graphical abstract

11 pages, 1487 KiB

Open AccessArticle

Characterization and Optimization of Isotachophoresis Parameters for Pacific Blue Succinimidyl Ester Dye on a PDMS Microfluidic Chip

by Himali Somaweera, Zachary Estlack, Jasmine Pramila Devadhasan, Jungtae Kim and Jungkyu Kim

Micromachines 2020, 11(11), 951; https://doi.org/10.3390/mi11110951 - 22 Oct 2020

Cited by 4 | Viewed by 2514

Abstract

Isotachophoresis (ITP) for Pacific Blue (PB) dye using a polydimethylsiloxane (PDMS) microfluidic chip is developed and characterized by determining the types and concentrations of electrolytes, the ITP duration, and the electric field density. Among candidate buffers for the trailing electrolyte (TE) and leading [...] Read more.

Isotachophoresis (ITP) for Pacific Blue (PB) dye using a polydimethylsiloxane (PDMS) microfluidic chip is developed and characterized by determining the types and concentrations of electrolytes, the ITP duration, and the electric field density. Among candidate buffers for the trailing electrolyte (TE) and leading electrolyte (LE), 40 mM borate buffer (pH 9) and 200 mM trisaminomethane hydrochloride (Tris-HCl) (pH 8) were selected to obtain the maximum preconcentration and resolution of the PB bands, respectively. With the selected TE and LE buffers, further optimization was performed to determine the electric field (EF) density and the ITP duration. These ITP parameters showed a 20–170,000 preconcentration ratio from initial PB concentrations of 10 nM–100 fM. Further demonstration was implemented to preconcentrate PB-conjugated lactate dehydrogenase (LDH) using the PDMS microfluidic chip. By utilizing the quenching nature of PB-LDH conjugation, we were able to identify concentrations of LDH as low as 10 ng/mL. This simple PDMS microfluidic chip-based ITP for PB preconcentration enables highly sensitive biological and chemical analyses by coupling with various downstream detection systems. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

15 pages, 6038 KiB

Open AccessArticle

Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

by Keyi Nan, Zhongyan Hu, Wei Zhao, Kaige Wang, Jintao Bai and Guiren Wang

Micromachines 2020, 11(9), 813; https://doi.org/10.3390/mi11090813 - 28 Aug 2020

Cited by 8 | Viewed by 1824

Abstract

In the present work, we studied the three-dimensional (3D) mean flow field in a micro electrokinetic (μEK) turbulence based micromixer by micro particle imaging velocimetry (μPIV) with stereoscopic method. A large-scale solenoid-type 3D mean flow field has been observed. The extraordinarily fast mixing [...] Read more.

In the present work, we studied the three-dimensional (3D) mean flow field in a micro electrokinetic (μEK) turbulence based micromixer by micro particle imaging velocimetry (μPIV) with stereoscopic method. A large-scale solenoid-type 3D mean flow field has been observed. The extraordinarily fast mixing process of the μEK turbulent mixer can be primarily attributed to two steps. First, under the strong velocity fluctuations generated by μEK mechanism, the two fluids with different conductivity are highly mixed near the entrance, primarily at the low electric conductivity sides and bias to the bottom wall. Then, the well-mixed fluid in the local region convects to the rest regions of the micromixer by the large-scale solenoid-type 3D mean flow. The mechanism of the large-scale 3D mean flow could be attributed to the unbalanced electroosmotic flows (EOFs) due to the high and low electric conductivity on both the bottom and top surface. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

18 pages, 1621 KiB

Open AccessArticle

Start-Up Electroosmotic Flow of Multi-Layer Immiscible Maxwell Fluids in a Slit Microchannel

by Juan Escandón, David Torres, Clara Hernández and René Vargas

Micromachines 2020, 11(8), 757; https://doi.org/10.3390/mi11080757 - 05 Aug 2020

Cited by 7 | Viewed by 2562

Abstract

In this investigation, the transient electroosmotic flow of multi-layer immiscible viscoelastic fluids in a slit microchannel is studied. Through an appropriate combination of the momentum equation with the rheological model for Maxwell fluids, an hyperbolic partial differential equation is obtained and semi-analytically solved [...] Read more.

In this investigation, the transient electroosmotic flow of multi-layer immiscible viscoelastic fluids in a slit microchannel is studied. Through an appropriate combination of the momentum equation with the rheological model for Maxwell fluids, an hyperbolic partial differential equation is obtained and semi-analytically solved by using the Laplace transform method to describe the velocity field. In the solution process, different electrostatic conditions and electro-viscous stresses have to be considered in the liquid-liquid interfaces due to the transported fluids content buffer solutions based on symmetrical electrolytes. By adopting a dimensionless mathematical model for the governing and constitutive equations, certain dimensionless parameters that control the start-up of electroosmotic flow appear, as the viscosity ratios, dielectric permittivity ratios, the density ratios, the relaxation times, the electrokinetic parameters and the potential differences. In the results, it is shown that the velocity exhibits an oscillatory behavior in the transient regime as a consequence of the competition between the viscous and elastic forces; also, the flow field is affected by the electrostatic conditions at the liquid-liquid interfaces, producing steep velocity gradients, and finally, the time to reach the steady-state is strongly dependent on the relaxation times, viscosity ratios and the number of fluid layers. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

20 pages, 5101 KiB

Open AccessArticle

A Numerical Investigation of Enhancing Microfluidic Heterogeneous Immunoassay on Bipolar Electrodes Driven by Induced-Charge Electroosmosis in Rotating Electric Fields

by Zhenyou Ge, Hui Yan, Weiyu Liu, Chunlei Song, Rui Xue and Yukun Ren

Micromachines 2020, 11(8), 739; https://doi.org/10.3390/mi11080739 - 30 Jul 2020

Cited by 5 | Viewed by 2903

Abstract

A unique approach is proposed to boost on-chip immuno-sensors, for instance, immunoassays, wherein an antibody immobilized on the walls of a microfluidic channel binds specifically to an antigen suspended freely within a working fluid. The performance of these sensors can be limited in [...] Read more.

A unique approach is proposed to boost on-chip immuno-sensors, for instance, immunoassays, wherein an antibody immobilized on the walls of a microfluidic channel binds specifically to an antigen suspended freely within a working fluid. The performance of these sensors can be limited in both susceptibility and response speed by the slow diffusive mass transfer of the analyte to the binding surface. Under appropriate conditions, the binding reaction of these heterogeneous immuno-assays may be enhanced by electroconvective stirring driven by external AC electric fields to accelerate the translating motion of antigens towards immobilized antibodies. To be specific, the phenomenon of induced-charge electroosmosis in a rotating electric field (ROT-ICEO) is fully utilized to stir analyte in the vicinity of the functionalized surface of an ideally polarizable floating electrode in all directions inside a tri-dimensional space. ROT-ICEO appears as a consequence of the action of a circularly-polarized traveling wave signal on its own induced rotary Debye screening charge within a bipolar induced double layer formed on the central floating electrode, and thereby the pertinent electrokinetic streamlines exhibit a radially converging pattern that greatly facilitates the convective transport of receptor towards the ligand. Numerical simulations indicate that ROT-ICEO can enhance the antigen–antibody binding reaction more effectively than convectional nonlinear electroosmosis driven by standing wave AC signals. The effectiveness of ROT-ICEO micro-stirring is strongly dependent on the Damkohler number as well as the Peclet number if the antigens are carried by a continuous base flow. Our results provide a promising way for achieving a highly efficient heterogeneous immunoassay in modern micro-total-analytical systems. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

13 pages, 2608 KiB

Open AccessArticle

The Influence of Electric Field Intensity and Particle Length on the Electrokinetic Transport of Cylindrical Particles Passing through Nanopore

by Liuyong Shi, Xiaohan He, Jian Ge, Teng Zhou, Ting Li and Sang Woo Joo

Micromachines 2020, 11(8), 722; https://doi.org/10.3390/mi11080722 - 25 Jul 2020

Cited by 4 | Viewed by 2079

Abstract

The electric transport of nanoparticles passing through nanopores leads to a change in the ion current, which is essential for the detection technology of DNA sequencing and protein determination. In order to further illustrate the electrokinetic transport mechanism of particles passing through nanopores, [...] Read more.

The electric transport of nanoparticles passing through nanopores leads to a change in the ion current, which is essential for the detection technology of DNA sequencing and protein determination. In order to further illustrate the electrokinetic transport mechanism of particles passing through nanopores, a fully coupled continuum model is constructed by using the arbitrary Lagrangian–Eulerian (ALE) method. The model consists of the electric field described by the Poisson equation, the concentration field described by Nernst–Planck equation, and the flow field described by the Navier–Stokes equation. Based on this model, the influence of imposed electric field and particle length on the electrokinetic transport of cylindrical particles is investigated. It is found firstly the translation velocities for the longer particles remain constant when they locate inside the nanopore. Both the ion current blockade effect and the ion current enhancement effect occur when cylindrical particles enter and exit the nanopore, respectively, for the experimental parameters employed in this research. Moreover, the particle translation velocity and current fluctuation amplitude are dominated by the electric field intensity, which can be used to adjust the particle transmission efficiency and the ion current detectability. In addition, the increase in particle length changes the particle position corresponding to the peak value of the ion current, which contributes to distinguishing particles with different lengths as well. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

15 pages, 3924 KiB

Open AccessArticle

Dielectrophoretic Separation of Particles Using Microfluidic Chip with Composite Three-Dimensional Electrode

by Li Chen, Xing Liu, Xiaolin Zheng, Xiaoling Zhang, Jun Yang, Tian Tian and Yanjian Liao

Micromachines 2020, 11(7), 700; https://doi.org/10.3390/mi11070700 - 20 Jul 2020

Cited by 19 | Viewed by 2984

Abstract

Integrating three-dimensional (3D) microelectrodes on microfluidic chips based on polydimethylsiloxane (PDMS) has been a challenge. This paper introduces a composite 3D electrode composed of Ag powder (particle size of 10 nm) and PDMS. Ethyl acetate is added as an auxiliary dispersant during the [...] Read more.

Integrating three-dimensional (3D) microelectrodes on microfluidic chips based on polydimethylsiloxane (PDMS) has been a challenge. This paper introduces a composite 3D electrode composed of Ag powder (particle size of 10 nm) and PDMS. Ethyl acetate is added as an auxiliary dispersant during the compounding process. A micromachining technique for processing 3D microelectrodes of any shape and size was developed to allow the electrodes to be firmly bonded to the PDMS chip. Through theoretical calculations, numerical simulations, and experimental verification, the role of the composite 3D microelectrodes in separating polystyrene particles of three different sizes via dielectrophoresis was systematically studied. This microfluidic device separated 20-, 10-, and 5-μm polystyrene particles nondestructively, efficiently, and accurately. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

13 pages, 2588 KiB

Open AccessArticle

Investigation on the Stability of Random Vortices in an Ion Concentration Polarization Layer with Imposed Normal Fluid Flow

by Jihye Choi, Ali Mani, Hyomin Lee and Sung Jae Kim

Micromachines 2020, 11(5), 529; https://doi.org/10.3390/mi11050529 - 22 May 2020

Cited by 7 | Viewed by 2482

Abstract

While nanoscale electrokinetic studies based on ion concentration polarization has been actively researched recently, random vortices naturally occur, leading to significantly destabilize in laboratory experiments or practical applications. These random vortices agitate the fluid inside microchannels and let the sample molecules seriously leak [...] Read more.

While nanoscale electrokinetic studies based on ion concentration polarization has been actively researched recently, random vortices naturally occur, leading to significantly destabilize in laboratory experiments or practical applications. These random vortices agitate the fluid inside microchannels and let the sample molecules seriously leak out preventing them from being controlled. Therefore, several trials have been reported to regulate those uninvited fluctuations by fluid flow tangential to a nanoporous membrane. Indeed, the influence of normal flow should be studied since the mass transport happens in the normal direction to the membrane. Thus, in this work, the nonlinear influence of normal flow to the instability near ion-selective surface was investigated by fully-coupled direct numerical simulation using COMSOL Multiphysics. The investigation on the effect of normal flow revealed that a space charge layer plays a significant role in the onset and growth of instability. The normal flow from the reservoir into the ion-selective surface pushed the space charge layer and decreased the size of vortices. However, there existed a maximum point for the growth of instability. The squeeze of the space charge layer increased the gradient of ion concentration in the layer, which resulted in escalating the velocity of vortices. On the other hand, the normal flow from the ion-selective surface into the reservoir suppressed the instability by spreading ions in the expanding space charge layer, leading to the reduction of ion concentration delayed the onset of instability. These two different mechanisms rendered asymmetric transition of stability as a function of the Peclet number and applied voltage. Therefore, this investigation would help understand the growth of instability and control the inevitable random vortices for the inhibition of fluid-agitation and leakage. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

14 pages, 4341 KiB

Open AccessArticle

Breakup Dynamics of Semi-dilute Polymer Solutions in a Microfluidic Flow-focusing Device

by Chun-Dong Xue, Xiao-Dong Chen, Yong-Jiang Li, Guo-Qing Hu, Tun Cao and Kai-Rong Qin

Micromachines 2020, 11(4), 406; https://doi.org/10.3390/mi11040406 - 14 Apr 2020

Cited by 7 | Viewed by 2660

Abstract

Droplet microfluidics involving non-Newtonian fluids is of great importance in both fundamental mechanisms and practical applications. In the present study, breakup dynamics in droplet generation of semi-dilute polymer solutions in a microfluidic flow-focusing device were experimentally investigated. We found that the filament thinning [...] Read more.

Droplet microfluidics involving non-Newtonian fluids is of great importance in both fundamental mechanisms and practical applications. In the present study, breakup dynamics in droplet generation of semi-dilute polymer solutions in a microfluidic flow-focusing device were experimentally investigated. We found that the filament thinning experiences a transition from a flow-driven to a capillary-driven regime, analogous to that of purely elastic fluids, while the highly elevated viscosity and complex network structures in the semi-dilute polymer solutions induce the breakup stages with a smaller power-law exponent and extensional relaxation time. It is elucidated that the elevated viscosity of the semi-dilute solution decelerates filament thinning in the flow-driven regime and the incomplete stretch of polymer molecules results in the smaller extensional relaxation time in the capillary-driven regime. These results extend the understanding of breakup dynamics in droplet generation of non-Newtonian fluids and provide guidance for microfluidic synthesis applications involving dense polymeric fluids. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

15 pages, 3964 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Controllable pH Manipulations in Micro/Nanofluidic Device Using Nanoscale Electrokinetics

by Jae Suk Park, Jeewhan Oh and Sung Jae Kim

Micromachines 2020, 11(4), 400; https://doi.org/10.3390/mi11040400 - 10 Apr 2020

Cited by 6 | Viewed by 2838

Abstract

Recently introduced nanoscale electrokinetic phenomenon called ion concentration polarization (ICP) has been suffered from serious pH changes to the sample fluid. A number of studies have focused on the origin of pH changes and strategies for regulating it. Instead of avoiding pH changes, [...] Read more.

Recently introduced nanoscale electrokinetic phenomenon called ion concentration polarization (ICP) has been suffered from serious pH changes to the sample fluid. A number of studies have focused on the origin of pH changes and strategies for regulating it. Instead of avoiding pH changes, in this work, we tried to demonstrate new ways to utilize this inevitable pH change. First, one can obtain a well-defined pH gradient in proton-received microchannel by applying a fixed electric current through a proton exchange membrane. Furthermore, one can tune the pH gradient on demand by adjusting the proton mass transportation (i.e., adjusting electric current). Secondly, we demonstrated that the occurrence of ICP can be examined by sensing a surrounding pH of electrolyte solution. When pH > threshold pH, patterned pH-responsive hydrogel inside a straight microchannel acted as a nanojunction to block the microchannel, while it did as a microjunction when pH < threshold pH. In case of forming a nanojunction, electrical current significantly dropped compared to the case of a microjunction. The strategies that presented in this work would be a basis for useful engineering applications such as a localized pH stimulation to biomolecules using tunable pH gradient generation and portable pH sensor with pH-sensitive hydrogel. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

11 pages, 1830 KiB

Open AccessArticle

Continuous Microfluidic Purification of DNA Using Magnetophoresis

by Ying Xu, Zhen Zhang, Zhen Su, Xiaoxiang Zhou, Xiaoming Han and Quanjun Liu

Micromachines 2020, 11(2), 187; https://doi.org/10.3390/mi11020187 - 11 Feb 2020

Cited by 18 | Viewed by 4201

Abstract

Automatic microfluidic purification of nucleic acid is predictable to reduce the input of original samples and improve the throughput of library preparation for sequencing. Here, we propose a novel microfluidic system using an external NdFeB magnet to isolate DNA from the polymerase chain [...] Read more.

Automatic microfluidic purification of nucleic acid is predictable to reduce the input of original samples and improve the throughput of library preparation for sequencing. Here, we propose a novel microfluidic system using an external NdFeB magnet to isolate DNA from the polymerase chain reaction (PCR) mixture. The DNA was purified and isolated when the DNA-carrying beads transported to the interface of multi-laminar flow under the influence of magnetic field. Prior to the DNA recovery experiments, COMSOL simulations were carried out to study the relationship between trajectory of beads and magnet positions as well as fluid velocities. Afterwards, the experiments to study the influence of varying velocities and input of samples on the DNA recovery were conducted. Compared to experimental results, the relative error of the final position of beads is less than 10%. The recovery efficiency decreases with increase of input or fluid velocity, and the maximum DNA recovery efficiency is 98.4% with input of l00 ng DNA at fluid velocity of 1.373 mm/s. The results show that simulations significantly reduce the time for parameter adjustment in experiments. In addition, this platform uses a basic two-layer chip to realize automatic DNA isolation without any other liquid switch value or magnet controller. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

8 pages, 2429 KiB

Open AccessArticle

Generation and Transport of Dielectric Droplets along Microchannels by Corona Discharge

by Qiang Tang, Shangru Zhou, Ruiheng Hu, Huai Zheng, Junheng Pan and Jau Tang

Micromachines 2020, 11(2), 181; https://doi.org/10.3390/mi11020181 - 10 Feb 2020

Cited by 4 | Viewed by 2179

Abstract

In this paper, a phenomenon of generation and transport of droplets is proposed, which is based on the dielectric liquid electroconvection induced by corona discharge. We placed the dielectric fluid on a conductive/nonconductive substrate, and then it broke apart to become many small [...] Read more.

In this paper, a phenomenon of generation and transport of droplets is proposed, which is based on the dielectric liquid electroconvection induced by corona discharge. We placed the dielectric fluid on a conductive/nonconductive substrate, and then it broke apart to become many small droplets that move along the conductive microchannel. The behaviors of dielectric droplets were experimentally observed on different conductive microchannels in details. Spreading speeds and sizes of dielectric droplets were analyzed at different driving voltages and conductive microchannels. This work highlights a simple approach to produce and manipulate dielectric droplets along microchannels. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

13 pages, 2494 KiB

Open AccessArticle

Driving Waveform Design with Rising Gradient and Sawtooth Wave of Electrowetting Displays for Ultra-Low Power Consumption

by Wei Li, Li Wang, Taiyuan Zhang, Shufa Lai, Linwei Liu, Wenyao He, Guofu Zhou and Zichuan Yi

Micromachines 2020, 11(2), 145; https://doi.org/10.3390/mi11020145 - 28 Jan 2020

Cited by 29 | Viewed by 2714

Abstract

As a kind of paper-like display technology, power consumption is a very important index for electrowetting displays (EWDs). In this paper, the influence of driving waveforms on power consumption of the EWDs is analyzed, and a driving waveform with rising gradient and sawtooth [...] Read more.

As a kind of paper-like display technology, power consumption is a very important index for electrowetting displays (EWDs). In this paper, the influence of driving waveforms on power consumption of the EWDs is analyzed, and a driving waveform with rising gradient and sawtooth wave is designed to reduce the power consumption. There are three stages in the proposed driving waveform. In the initial stage, the driving voltage is raised linearly from the threshold to the maximum value to reduce the invalid power consumption. At the same time, the oil breakup can be prohibited. And then, a section of sawtooth wave is added for suppressing oil backflow. Finally, there is a section of resetting wave to eliminate the influence of charge leakage. Experimental results show that the power consumption of the ultra-low power driving waveform is 1.85 mW, which is about 38.13% lower than that of the conventional used square wave (2.99 mW), when the aperture ratio is 65%. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

12 pages, 3675 KiB

Open AccessArticle

A Liquid-Metal-Based Dielectrophoretic Microdroplet Generator

by Ronghang Wang, Lunjia Zhang, Meng Gao, Qifu Wang, Zhongshan Deng and Lin Gui

Micromachines 2019, 10(11), 769; https://doi.org/10.3390/mi10110769 - 11 Nov 2019

Cited by 7 | Viewed by 2727

Abstract

This paper proposes a novel microdroplet generator based on the dielectrophoretic (DEP) force. Unlike the conventional continuous microfluidic droplet generator, this droplet generator is more like “invisible electric scissors”. It can cut the droplet off from the fluid matrix and modify droplets’ length [...] Read more.

This paper proposes a novel microdroplet generator based on the dielectrophoretic (DEP) force. Unlike the conventional continuous microfluidic droplet generator, this droplet generator is more like “invisible electric scissors”. It can cut the droplet off from the fluid matrix and modify droplets’ length precisely by controlling the electrodes’ length and position. These electrodes are made of liquid metal by injection. By applying a certain voltage on the liquid-metal electrodes, the electrodes generate an uneven electric field inside the main microfluidic channel. Then, the uneven electric field generates DEP force inside the fluid. The DEP force shears off part from the main matrix, in order to generate droplets. To reveal the mechanism, numerical simulations were performed to analyze the DEP force. A detailed experimental parametric study was also performed. Unlike the traditional droplet generators, the main separating force of this work is DEP force only, which can produce one droplet at a time in a more precise way. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Graphical abstract

15 pages, 4298 KiB

Open AccessArticle

A Driving System for Fast and Precise Gray-Scale Response Based on Amplitude–Frequency Mixed Modulation in TFT Electrowetting Displays

by Zichuan Yi, Linwei Liu, Li Wang, Wei Li, Lingling Shui and Guofu Zhou

Micromachines 2019, 10(11), 732; https://doi.org/10.3390/mi10110732 - 29 Oct 2019

Cited by 32 | Viewed by 2693

Abstract

The gray-scale display which is driven by PWM (pulse width modulation) in TFT (thin film transistor) electrowetting displays (EWDs) has some shortcomings, such as large amplitude of oil oscillation in pixels and slow response speed for displaying gray scale. In this paper, an [...] Read more.

The gray-scale display which is driven by PWM (pulse width modulation) in TFT (thin film transistor) electrowetting displays (EWDs) has some shortcomings, such as large amplitude of oil oscillation in pixels and slow response speed for displaying gray scale. In this paper, an amplitude–frequency mixed modulation driving system is proposed to improve the response speed of driving gray scale and enhance the oil stability when the gray scale is displayed. In the initial stage of the driving process, the oil is driven by a high voltage to close to the target luminance, and the driving voltage is then decreased to stabilize the oil. The electrowetting hysteresis curve was used to calculate the relation model between the driving voltage and the luminance of the pixel in the system, and the driving voltage value of the pixel at each driving stage was then set to make the oil precisely and rapidly stabilize at the target luminance value. In the output driving platform, the amplitude–frequency mixed modulation is realized based on the source IC, which was used to realize digital-to-analog conversion. An 8 inch EWD was tested using an Admesy colorimeter, and the experimental results show that the pixel response time is reduced by 70% and the gray-scale oscillation is reduced by 80%. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Graphical abstract

Review

Jump to: Research

30 pages, 5835 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Electro-Hydrodynamics of Emulsion Droplets: Physical Insights to Applications

by Muhammad Salman Abbasi, Ryungeun Song, Seongsu Cho and Jinkee Lee

Micromachines 2020, 11(10), 942; https://doi.org/10.3390/mi11100942 - 18 Oct 2020

Cited by 20 | Viewed by 5226

Abstract

The field of droplet electrohydrodynamics (EHD) emerged with a seminal work of G.I. Taylor in 1966, who presented the so-called leaky dielectric model (LDM) to predict the droplet shapes undergoing distortions under an electric field. Since then, the droplet EHD has evolved in [...] Read more.

The field of droplet electrohydrodynamics (EHD) emerged with a seminal work of G.I. Taylor in 1966, who presented the so-called leaky dielectric model (LDM) to predict the droplet shapes undergoing distortions under an electric field. Since then, the droplet EHD has evolved in many ways over the next 55 years with numerous intriguing phenomena reported, such as tip and equatorial streaming, Quincke rotation, double droplet breakup modes, particle assemblies at the emulsion interface, and many more. These phenomena have a potential of vast applications in different areas of science and technology. This paper presents a review of prominent droplet EHD studies pertaining to the essential physical insight of various EHD phenomena. Here, we discuss the dynamics of a single-phase emulsion droplet under weak and strong electric fields. Moreover, the effect of the presence of particles and surfactants at the emulsion interface is covered in detail. Furthermore, the EHD of multi-phase double emulsion droplet is included. We focus on features such as deformation, instabilities, and breakups under varying electrical and physical properties. At the end of the review, we also discuss the potential applications of droplet EHD and various challenges with their future perspectives. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Graphical abstract

24 pages, 4470 KiB

Open AccessReview

Determination of Dielectric Properties of Cells using AC Electrokinetic-based Microfluidic Platform: A Review of Recent Advances

by Wenfeng Liang, Xieliu Yang, Junhai Wang, Yuechao Wang, Wenguang Yang and Lianqing Liu

Micromachines 2020, 11(5), 513; https://doi.org/10.3390/mi11050513 - 19 May 2020

Cited by 26 | Viewed by 4037

Abstract

Cell dielectric properties, a type of intrinsic property of cells, can be used as electrophysiological biomarkers that offer a label-free way to characterize cell phenotypes and states, purify clinical samples, and identify target cancer cells. Here, we present a review of the determination [...] Read more.

Cell dielectric properties, a type of intrinsic property of cells, can be used as electrophysiological biomarkers that offer a label-free way to characterize cell phenotypes and states, purify clinical samples, and identify target cancer cells. Here, we present a review of the determination of cell dielectric properties using alternating current (AC) electrokinetic-based microfluidic mechanisms, including electro-rotation (ROT) and dielectrophoresis (DEP). The review covers theoretically how ROT and DEP work to extract cell dielectric properties. We also dive into the details of differently structured ROT chips, followed by a discussion on the determination of cell dielectric properties and the use of these properties in bio-related applications. Additionally, the review offers a look at the future challenges facing the AC electrokinetic-based microfluidic platform in terms of acquiring cell dielectric parameters. Our conclusion is that this platform will bring biomedical and bioengineering sciences to the next level and ultimately achieve the shift from lab-oriented research to real-world applications. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Electrokinetics in Micro-/nanofluidic Devices

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Published Papers (17 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI