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1.
Electrophoresis ; 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31943244

RESUMO

We study herein numerically the use of induced-charge electrokinetic phenomena to enable a flexible control of ion transport of dilute electrolyte in a straight ion concentration polarization system. The effect of three convection modes of induced-charge electrokinetic phenomena, including induced-charge electroosmosis, flow-field effect transistor, and alternating-current electroosmosis (ACEO), on convective arrestment of diffusive wave-front propagation is investigated by developing a cross-scale and fully coupled transient numerical simulation model, wherein multiple frequency electrochemical polarization and nonlinear diffuse charge dynamics in spatiotemporally varying solution conductivity are taken into account. We demonstrate by detailed comparative simulation studies that ACEO vortex flow field above a metal strip array arranged along the anodic chamber's bottom surface serves as the most efficient way for adjusting the salt density distribution at micrometer and even millimeter dimension, due to its high flexibility in controlling the stirring flow state with the introduction of two extra electrical parameters. The specific operating status is determined by whether the electrode array is floating in potential (induced-charge electroosmosis) or biased to ground (flow-field effect transistor) or forced to oscillate at another Fourier mode (ACEO). These results prove useful for on-chip electric current control with electroconvective stirring.

2.
Anal Chem ; 92(3): 2778-2786, 2020 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-31909587

RESUMO

We present a novel approach that utilizes thermal buoyancy convection to achieve flexible particle focusing and switching in continuous flow of a microfluidic system. In this platform, three strip microheaters, A, B, and C, are symmetrically distributed at the bottom of microchannel, and they are isolated from the particle suspension by a thin glass slide. Continual transverse convection flow forms when the microheaters are energized by dc signals. The flow patterns are readily tuned by changing the energization strategies of the microheater array, leading to the modulation of the position of flow stagnation region. Accordingly, microparticles dispersed in fluids are rapidly focused to the flow stagnation region by the Stokes drag and thus form a continuous particle beam. The particle beam can also be switched to different lateral positions by adjusting the control voltages. This particle manipulation method is first demonstrated by respectively energizing these three microheaters and subsequently switching silica particles into different outlets. The lateral position of the particle beam then is flexibly controlled by simultaneously energizing microheaters A and B (or B and C) and adjusting the voltage applied on microheater A (or C). Furthermore, the versatility of this approach is proved by focusing and switching of microsized droplets, that is, oil-in-water and water-in-oil-in-water emulsion droplets. Finally, we use poly(ethylene glycol) diacrylate microgels, excellent reactant carriers, as an experimental sample and flexibly manipulate them in this microdevice, demonstrating this strategy's applicability for the cargo delivery. Therefore, this technique can be attractive for many particle preprocessing applications.

3.
Anal Chim Acta ; 1096: 108-119, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31883577

RESUMO

Efficient granular sample manipulation is crucial for various microfluidic-based applications such as material synthesis and drug delivery. Herein we present a novel method to efficiently manipulate microbeads and droplets using the combined thermal buoyancy convection and temperature-enhanced rotating induced-charge electroosmotic flow. Within the granular fluid, a pair of counter-rotating microvortices is formed above the floating electrode, leading to the formation of a flow stagnation region at the bottom center. Granular samples then can be effectively transported to this region by the Stokes drag, and the concentration performance can be flexibly manipulated by adjusting the energization strategies of the chip. The contributions of fluid convection, dielectrophoresis, thermophoresis, and gravity force to particle migration are first studied and compared, proving that the convection flow and gravity force are mainly responsible for particle migration and deposition respectively. Then the systematic enriching experiments of 4-µm silica particles demonstrate that the particle migration velocity can be highly improved by the combined thermal-electrical field. Finally, the effective concentration of nanocopper particles and the assembly of oil-in-water/water-in-oil-in-water droplets indicate that this approach is capable of manipulating diverse granular samples. Therefore, this strategy can be attractive for lots of microfluidic-based applications because of its high efficiency and simplicity.

4.
Lab Chip ; 19(17): 2936-2946, 2019 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-31380864

RESUMO

It is becoming more difficult to use bulk mixing and bi-fluid micromixing in multi-step continuous-flow reactions, multicomponent reactions, and nanoparticle synthesis because they typically involve multiple reactants. To date, most micromixing studies, both passive and active, have focused on how to efficiently mix two fluids, while micromixing of three or more fluids together (multi-fluid mixing) has been rarely explored. This study is the first on tri-fluid mixing in microchannels. We investigated tri-fluid mixing in three microchannel models: a straight channel, a classical staggered herringbone mixing (SHM) channel, and a three-dimensional (3D) X-crossing microchannel. Numerical simulations and experiments were jointly conducted. A two-step experimental process was performed to determine the tri-fluid mixing efficiencies of these microchannels. We found that the SHM cannot significantly enhance mixing of three streams especially for a Reynolds number (Re) higher than 10. However, the 3D X-crossing channel based on splitting-and-recombination (SAR) showed effective tri-mixing performance over a wide Re range up to 275 (with a corresponding flow rate of 1972.5 µL min-1), thereby enabling high microchannel throughput. Furthermore, this tri-fluid micromixing process was used to synthesize a kind of Si-based nanoparticle. This achieved a narrower particle size distribution than traditional bulk mixing. Therefore, SAR-based tri-fluid mixing is an alternative for chemical and biochemical reactions where three reactants need to be mixed.

5.
Small ; 15(42): e1903098, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31464378

RESUMO

The separate co-encapsulation and selective controlled release of multiple encapsulants in a predetermined sequence has potentially important applications for drug delivery and tissue engineering. However, the selective controlled release of distinct contents upon one triggering event for most existing microcarriers still remains challenging. Here, novel microfluidic fabrication of compound-droplet-pairs-filled hydrogel microfibers (C-Fibers) is presented for two-step selective controlled release under AC electric field. The parallel arranged compound droplets enable the separate co-encapsulation of distinct contents in a single microfiber, and the release sequence is guaranteed by the discrepancy of the shell thickness or core conductivity of the encapsulated droplets. This is demonstrated by using a high-frequency electric field to trigger the first burst release of droplets with higher conductivity or thinner shell, followed by the second release of the other droplets under low-frequency electric field. The reported C-Fibers provide novel multidelivery system for a wide range of applications that require controlled release of multiple ingredients in a prescribed sequence.

6.
Micromachines (Basel) ; 10(7)2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31277290

RESUMO

We present herein a unique concept of multifrequency induced-charge electroosmosis (MICEO) actuated directly on driving electrode arrays, for highly-efficient simultaneous transport and convective mixing of fluidic samples in microscale ducts. MICEO delicately combines transversal AC electroosmotic vortex flow, and axial traveling-wave electroosmotic pump motion under external dual-Fourier-mode AC electric fields. The synthetic flow field associated with MICEO is mathematically analyzed under thin layer limit, and the particle tracing experiment with a special powering technique validates the effectiveness of this physical phenomenon. Meanwhile, the simulation results with a full-scale 3D computation model demonstrate its robust dual-functionality in inducing fully-automated analyte transport and chaotic stirring in a straight fluidic channel embedding double-sided quarter-phase discrete electrode arrays. Our physical demonstration with multifrequency signal control on nonlinear electroosmosis provides invaluable references for innovative designs of multifunctional on-chip analytical platforms in modern microfluidic systems.

7.
Analyst ; 144(17): 5150-5163, 2019 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-31342972

RESUMO

Five arc-shaped gaps were designed on the bipolar electrode to actuate alternately opposite-direction asymmetrical induced-charge electro-osmosis (AICEO) vortices, and we developed a microfluidic device using such asymmetrical vortices to realize particle separation. When the buoyancy force dominates in the vertical direction, particles stay at the channel bottom, experiencing a left deflection under the vortices in the convex arc areas. In contrast, when the levitation force induced by AICEO vortices overcomes the buoyancy force, particles are elevated to a high level and captured by right vortices, undergoing a right deflection under the vortices in the concave arc areas. Moreover, when particles pass through the concave or convex arc areas every time, their right or left deflections are enlarged gradually and the separation becomes more complete. Remarkably, as the light/small particles at low voltage, heavy/large particles can be elevated to a new high level and undergo right deflection by increasing the voltage. We first explicitly proved the separation principle and analyzed numerically its capability in density- and size-based separation. Depending on the study of the voltage-dependent AICEO characterization of 4 µm silica and 4 µm PMMA particles, we experimentally verified the feasibility of our device in density-based separation. According to the investigation of sensitivity to particle size, we separated multi-sized yeast cells to confirm the capability of our device in size-based separation. Finally, we extracted yeast cells from impeding particles, obtaining 96% purity. Additionally, we designed a 500 µm distance between the focusing and separation region to circumvent the problems caused by electric-field interaction. Our AICEO-based separation method holds potential to serve as a useful tool in transesterification of microalgal lipids to biodiesel and solar cell processing because of its outstanding advantages, such as gentle conditions, contact-free separation, high-sensitivity and high-efficiency separation capability.

8.
Talanta ; 200: 177-185, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31036171

RESUMO

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (µPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DµPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions.


Assuntos
Automação , Papel , Troponina I/análise , Colorimetria/economia , Colorimetria/instrumentação , Técnicas Eletroquímicas/economia , Técnicas Eletroquímicas/instrumentação , Técnicas Analíticas Microfluídicas/economia , Técnicas Analíticas Microfluídicas/instrumentação
9.
Anal Chem ; 91(9): 5729-5738, 2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-30938976

RESUMO

We propose a simplified multifunctional traffic control approach that effectively combines dielectrophoresis (DEP) and alternating current electrothermal (ACET) flow to realize continuous particle trapping, switching, and sorting. In the designed microsystem, the combined DEP and ACET effects, which are symmetrically generated above a bipolar electrode surface, contribute to focus the incoming colloidal particles into a thin beam. Once the bipolar electrode is energized with an electric gate signal completely in phase with the driving alternating current (AC) signal, the spatial symmetry of the electric field can be artificially reordered by adjusting the gate voltage through field-effect traffic control. This results in a reshapable field stagnant region for precise switching of particles into the region of interest. Moreover, the integrated particle switching prior to the scaled particle trapping experiment is successfully conducted to demonstrate the feasibility of the combined strategy. Furthermore, a mixture of two types of particle sorting (i.e., density, size) with quick response performance is achieved by increasing the driving voltage with a maximum gate voltage offset, thus, extending the versatility of the designed device. Finally, droplet switching and filtration of the satellite droplets from the parent droplets is performed to successfully permit control of the droplet traffic. The proposed traffic control approach provides a promising technique for flexible manipulation of particulate samples and can be conveniently integrated with other micro/nanofluidic components into a complete functional on-chip platform owing to its simple geometric structure, easy operation, and multifunctionality.

10.
Electrophoresis ; 40(20): 2683-2698, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-30883820

RESUMO

The phenomenon of electrothermal (ET) convection has recently captured great attention for transporting fluidic samples in microchannels embedding simple electrode structures. In the classical model of ET-induced flow, a conductivity gradient of buffer medium is supposed to arise from temperature-dependent electrophoretic mobility of ionic species under uniform salt concentrations, so it may not work well in the presence of evident concentration perturbation within the background electrolyte. To solve this problem, we develop herein a microscopic physical description of ET streaming by fully coupling a set of Poisson-Nernst-Planck-Navier-Stokes equations and temperature-dependent fluid physicochemical properties. A comparative study on a standard electrokinetic micropump exploiting asymmetric electrode arrays indicates that, our microscopic model always predicts a lower ET pump flow rate than the classical macroscopic model even with trivial temperature elevation in the liquid. Considering a continuity of total current density in liquids of inhomogeneous polarizability, a moderate degree of fluctuation in ion concentrations on top of the electrode array is enough to exert a significant influence on the induction of free ionic charges, rendering the enhanced numerical treatment much closer to realistic experimental measurement. Then, by placing a pair of thin-film resistive heaters on the bottom of an anodic channel interfacing a cation-exchange medium, we further provide a vivid demonstration of the enhanced model's feasibility in accurately resolving the combined Coulomb force due to the coexistence of an extended space charge layer and smeared interfacial polarizations in an externally-imposed temperature gradient, while this is impossible with conventional linear approximation. This leads to a reliable method to achieve a flexible regulation on spatial-temporal evolution of ion-depletion layer by electroconvective mixing. These results provide useful insights into ET-based flexible control of micro/nanoscale solid entities in modern micro-total-analytical systems.

11.
Nanoscale ; 11(13): 6410-6421, 2019 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-30888357

RESUMO

Vortex-based separation is a promising method in particle-particle separation and has only been demonstrated theoretically some years ago. To date, a continuous-flow separation device based on vortices has not been conceived because many known vortices were either unstable or controlling them lacked precision. Electro-convection from induced charge electro-osmosis (ICEO) has advantages, such as adjustable flow profiles, long-range actuation, and long-lived vortices, and offers an alternative means of particle separation. We found though a different ICEO focusing behaviour of particles whereby particles were trapped and concentrated in two vortex cores. Encouraged by these features of ICEO vortices, we proposed a direct method for particle separation in continuous flow. In various experiments, we first characterized the ICEO-induced focusing performances of various kinds of particle samples in a straight channel embedded with an individual central bipolar electrode, presenting a justifiable explanation. Second, the combined dependences of ICEO particle separation on the sample size and mass density were investigated. Third, an application to cell purification was performed in which we obtained a purity surpassing 98%. Finally, we investigated the ICEO characteristics of nanoparticles, exploiting our method in isolating nanoscale objects by separating 500 nm and 5 µm polystyrene beads, gaining clear separation. Certain features of this method, such as having ease of operation, simple structure, and continuous flow, and being prefocusing free and physical property-based, indicate its good potential in tackling environmental monitoring, cell sorting, chemical analysis, isolation of uniform-sized graphene and transesterification of micro-algal lipids to biodiesel.

12.
Anal Chem ; 91(7): 4457-4465, 2019 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-30817882

RESUMO

Thermal-based microparticle focusing has recently received increasing attention due to its noninvasive nature and simple manipulation mechanism. However, its further application is limited by current complicated fluid heating systems and low particle focusing velocity. Using simple indium tin oxide-made microheaters, herein we propose a flexible and novel approach for efficient particle focusing based on direct current-induced thermal buoyancy convection. Importantly, for avoiding possible electrochemical reactions on the electrode, the microheaters are isolated from the granular fluids of interest by a thin glass slide. The concentration performance of the designed chip was first demonstrated by statically focusing 4-µm silica particles, yeast cells, silica particles in insulating buffer, and 100-nm copper microspheres. Also the trapping of a mixture of 5-µm and 2-µm polystyrene microbeads indicated that the chip can either simultaneously concentrate two kinds of particles or selectively focus the heavier ones by adjusting the voltages. Then the different concentration patterns of microbeads exhibited that the microspheres can be flexibly manipulated by changing the configurations of microheaters. Furthermore, for the first time, we achieved thermal-based continuous particle focusing in both conducting and insulating solutions using buoyancy convection, demonstrating that this method can be utilized to achieve both static and continuous particle manipulations in multiple liquid media. Finally, the feasibility of this device in effective wear measurement of machines was demonstrated by conducting systematic experiments of focusing nanocopper particles in the hydraulic oil. Therefore, this presented approach would be promising for a broad range of on-chip applications.

13.
Electrophoresis ; 40(6): 979-992, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30256428

RESUMO

Induced-charge electroosmosis (ICEO) has attracted tremendous popularity for driving fluid motion from the microfluidic community since the last decade, while less attention has been paid to ICEO-based nanoparticle manipulation. We propose herein a unique concept of hybrid electroosmotic kinetics (HEK) in terms of bi-phase ICEO (BICEO) actuated in a four-terminal spiral electrode array, for effective electrokinetic enrichment of fluorescent polystyrene nanoparticles on ideally polarizable metal strips. First, by alternating the applied AC voltage waves between consecutive discrete terminals, the flow stagnation lines where the sample nanoparticles aggregate can be switched in time between two different distribution modes. Second, we innovatively introduce the idea of AC field-effect flow control on BICEO; by altering the combination of gating voltage sequence, not only the number of circulative particle trapping lines is doubled, but the collecting locations can be flexibly reconfigured as well. Third, hydrodynamic streaming of DC-biased BICEO is tested in our device design, wherein the global linear electroosmosis dominates BICEO contributed from both AC and DC components, resulting in a reduction of particle enrichment area, while with a sharp increase in sample transport speed inside the bulk phase. The flow field associated with HEK is predicted using a linear asymptotic analysis under Debye-Huckel limit, with the simulation results in qualitative agreement with in-lab observations of nanoparticle trapping by exploiting a series of improved ICEO techniques. This work provides an affordable and field-deployable platform for real-time nanoparticle trapping in the context of dilute electrolyte.


Assuntos
Eletro-Osmose/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Nanopartículas/química , Eletricidade , Eletro-Osmose/métodos , Desenho de Equipamento , Cinética , Microeletrodos
14.
Micromachines (Basel) ; 9(3)2018 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-30424036

RESUMO

Induced-charge electroosmosis has attracted lots of attention from the microfluidic community over the past decade. Most previous researches on this subject focused on induced-charge electroosmosis (ICEO) vortex streaming actuated on ideally polarizable surfaces immersed in electrolyte solutions. Starting from this point, we conduct herein a linear asymptotic analysis on nonlinear electroosmotic flow next to leaky dielectric blocks of arbitrary electrical conductivity and dielectric permittivity in harmonic AC electric fields, and theoretically demonstrate that observable ICEO fluid motion can be generated at high field frequencies in the vicinity of nearly insulating semiconductors, a very low electrical conductivity, of which can evidently increase the double-layer relaxation frequency (inversely proportional to the solid permittivity) to be much higher than the typical reciprocal RC time constant for induced double-layer charging on ideally polarizable surfaces. A computational model is developed to study the feasibility of this high-frequency vortex flow field of ICEO for sample mixing in microfluidics, in which the usage of AC voltage signal at high field frequencies may be beneficial to suppress electrochemical reactions to some extent. The influence of various parameters for developing an efficient mixer is investigated, and an integrated arrangement of semiconductor block array is suggested for achieving a reliable mixing performance at relatively high sample fluxes. Our physical demonstration with high-frequency ICEO next to leaky dielectric blocks using a simple channel structure offers valuable insights into the design of high-throughput micromixers for a variety of lab-on-a-chip applications.

15.
Micromachines (Basel) ; 9(4)2018 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-30424112

RESUMO

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.

16.
Micromachines (Basel) ; 9(9)2018 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-30424365

RESUMO

In this study, we make use of the AC field-effect flow control on induced-charge electroosmosis (ICEO), to develop an electrokinetic micromixer with 3D electrode layouts, greatly enhancing the device performance compared to its 2D counterpart of coplanar metal strips. A biased AC voltage wave applied to the central gate terminal, i.e., AC field-effect control, endows flow field-effect-transistor of ICEO the capability to produce arbitrary symmetry breaking in the transverse electrokinetic vortex flow pattern, which makes it fascinating for microfluidic mixing. Using the Debye-Huckel approximation, a mathematical model is established to test the feasibility of the new device design in stirring nanoparticle samples carried by co-flowing laminar streams. The effect of various experimental parameters on constructing a viable micromixer is investigated, and an integrated microdevice with a series of gate electrode bars disposed along the centerline of the channel bottom surface is proposed for realizing high-flux mixing. Our physical demonstration on field-effect nonlinear electroosmosis control in 3D electrode configurations provides useful guidelines for electroconvective manipulation of nanoscale objects in modern microfluidic systems.

17.
Micromachines (Basel) ; 9(2)2018 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-30393361

RESUMO

We present herein a novel method of bipolar field-effect control on DC electroosmosis (DCEO) from a physical point of view, in the context of an intelligent and robust operation tool for stratified laminar streams in microscale systems. In this unique design of the DC flow field-effect-transistor (DC-FFET), a pair of face-to-face external gate terminals are imposed with opposite gate-voltage polarities. Diffuse-charge dynamics induces heteropolar Debye screening charge within the diffuse double layer adjacent to the face-to-face oppositely-polarized gates, respectively. A background electric field is applied across the source-drain terminal and forces the face-to-face counterionic charge of reversed polarities into induced-charge electroosmotic (ICEO) vortex flow in the lateral direction. The chaotic turbulence of the transverse ICEO whirlpool interacts actively with the conventional plug flow of DCEO, giving rise to twisted streamlines for simultaneous DCEO pumping and ICEO mixing of fluid samples along the channel length direction. A mathematical model in thin-layer approximation and the low-voltage limit is subsequently established to test the feasibility of the bipolar DC-FFET configuration in electrokinetic manipulation of fluids at the micrometer dimension. According to our simulation analysis, an integrated device design with two sets of side-by-side, but upside-down gate electrode pair exhibits outstanding performance in electroconvective pumping and mixing even without any externally-applied pressure difference. Moreover, a paradigm of a microdevice for fully electrokinetics-driven analyte treatment is established with an array of reversed bipolar gate-terminal pairs arranged on top of the dielectric membrane along the channel length direction, from which we can obtain almost a perfect liquid mixture by using a smaller magnitude of gate voltages for causing less detrimental effects at a small Dukhin number. Sustained by theoretical analysis, our physical demonstration on bipolar field-effect flow control for the microfluidic device of dual functionalities in simultaneous electroconvective pumping and mixing holds great potential in the development of fully-automated liquid-phase actuators in modern microfluidic systems.

18.
ACS Appl Mater Interfaces ; 10(46): 40228-40237, 2018 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-30362341

RESUMO

Microfiber modules with controllable lengths emerged as novel biomimetic platforms and are significant for many tissue engineering applications. However, accurately controlling the length of microfibers on the scale of millimeter or even micrometer still remains challenging. Here, a novel and scalable strategy to generate microfiber modules with precisely tunable lengths ranging from 100 to 3500 µm via an alternating current (AC) electric field is presented. To control the microfiber length, double-emulsion droplets containing a chelating agent (sodium citrate) as a spacing node are first uniformly embedded in the microfibers in a controllable spatial arrangement. This process is precisely tuned by adjusting the flow rates, thus, tailoring the resulting multicompartmental microfiber structure. Next, an AC voltage signal is used to trigger the electric field-induced cutting process, where the time-averaged electrical force acting on the induced bipolar charge from the Maxwell-Wagner structural polarization mechanism breaks the stress balance at the interfaces, rupturing the double-emulsion droplets, and resulting in the burst release of the encapsulated chelating agents into the hydrogel cavity. The outer hydrogel shell is quickly dissolved by a chemical reaction, cutting the long fiber into a series of microfiber units of given length. Furthermore, adding magnetic nanoparticles endows magnetic functionality with these microfiber modules, which are allowed to serve as micromotors and building blocks. This electro-induced cutting method provides a facile strategy for the fabrication of microfibers with desired lengths, showing considerable promise for various chemical and biological applications.

19.
Anal Chem ; 90(19): 11376-11384, 2018 10 02.
Artigo em Inglês | MEDLINE | ID: mdl-30199243

RESUMO

Continuous sample switching is an essential process for developing an integrated platform incorporating multiple functionality with applications typically ranging from chemical to biological assays. Herein we propose a unique method of external-field-reconfigurable symmetry breaking in induced-charge electroosmosis above a simple planar bipolar electrode for continuous particle beam switching. In the proposed system, the spatial symmetry of a nonlinear electroosmotic vortex flow can be artificially reordered to achieve an asymmetric electrically floating-electrode polarization by regulating the configurations of the external ac signals, thus contributing to flexible particle beam switching. This switching system comprises an upstream flow-focusing region where particles are prefocused into a beam on the bipolar electrode by transversal electroconvective mass transfer, and a deflecting region in which the resulting particle beam is deflected to generate a steerable lateral displacement to enter the desired region via the action of an asymmetric polarization-induced reshapable electroosmotic flow stagnation line in a controllable background field gradient. A lateral particle displacement on the order of hundreds of micrometers can be achieved in a deterministic manner by varying the voltage, frequency, and inlet flow rate, thereby enabling multichannel particle switching. Furthermore, the versatility of the switching mechanism is extended by successfully accomplishing fluorescent nanoparticle beam switching, yeast cell switching, five-outlet particle switching, and simultaneous switching of two particle types. The proposed switching approach provides a promising technique for flexible electrokinetic sample preconcentration prior to any subsequent analysis and can be conveniently integrated with other micro/nanofluidic components into a complete functional on-chip platform owing to its simple electrode structure.

20.
Anal Chem ; 90(19): 11461-11469, 2018 10 02.
Artigo em Inglês | MEDLINE | ID: mdl-30192521

RESUMO

Microfluidic systems have been developed widely in scaled-down processes of laboratory techniques, but they are usually limited in achieving stand-alone functionalities. It is highly desirable to exploit an integrated microfluidic device with multiple capabilities such as cell separation, single-cell trapping, and cell manipulation. Herein, we reported a microfluidic platform integrated with actuation electrodes, for separating cells and microbeads, and bipolar electrodes, for trapping, rotating, and propelling single cells and microbeads. The separation of cells and microbeads can be first achieved by deflective dielectrophoresis (DEP) barriers. Trapping experiments with yeast cells and polystyrene (PS) microbeads suspended in aqueous solutions with different conductivities were then conducted, showing that both cells and particles can be trapped at the center of wireless electrodes by negative DEP force. Upon application of a rotating electric field, yeast cells exhibit translational movement along the electrode edges, and self-rotation is seen at an array of bipolar electrodes when electrorotational torque and traveling wave DEP force are applied on the cells. The current approach allows us to switch the propulsion and rotation direction of cells by varying the frequency of the applied electric field. Beyond the achievements of single-cell manipulation, this system permits effective control of several particles or cells simultaneously. The integration of parallel sorting and single trapping stages within a microfluidic chip enables the prospect of high-throughput cell separation, single trapping, and large-scale cell locomotion and rotation in a noninvasive and disposable format, showing great potential in single-cell analysis, targeted drug delivery, and surgery.


Assuntos
Separação Celular/métodos , Saccharomyces cerevisiae/isolamento & purificação , Separação Celular/instrumentação , Condutividade Elétrica , Eletrodos , Eletroforese , Dispositivos Lab-On-A-Chip , Microesferas , Poliestirenos
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