AC Electrokinetics Research Articles

Clarification of Colloidal Particles in Lake and River Water Using AC Electrokinetic

Scenery of clear water of a lake or river is always a fascinating view. The clarity of a water is subjected to the water free from colloidal particles. Lake or river usually have foreign colloidal particles such as sand, mud, foreign particle, etc. which make the water cloudy. Usually the cloudy water become clear because of natural sedimentation process. However it is not easy to clarify cloudy water of a lake or river and make it clear especially if the sediment of colloidal particle is influence or disturb by water current. The approach by AC Electrokinetic phenomenon able to manipulate colloidal particles in a suspension. It can separate, trap or sort colloidal particle which made the phenomenon as possible reliable option for clarifying lake or river water from colloidal particles hence make it clear water. This work will simulate the process of clarification of colloidal suspension using AC Electrokinetic phenomenon in a lab. Electrodes were fabricated on Indium Tin Oxide (ITO) coated glass slide using laser etching technique. The electrode which poses unique geometry will be able to demonstrate electric field gradient as soon as it is introduced with electrical signal. Base on the surface potential of the colloids and the surface potential of the electrode, the colloids will be manipulated. This phenomenon is known as AC Electrokinetics. This can be regarded as guided sedimentation process. The trapped colloidal particle can be now easily extracted or remove from the water thus transform the water from cloudy to clear hence complete water clarification process.

Trajectory Control of Self-Propelled Micromotors Using AC Electrokinetics.

3D control of the motion of self-powered micromotors is demonstrated using AC electrokinetics by applying an AC electric field on indium tin oxide transparent electrodes.

交流動電現象のマイクロチップバイオ分析への応用

交流動電現象のマイクロチップバイオ分析への応用

AC Electrokinetics of Physiological Fluids for Biomedical Applications.

Alternating current (AC) electrokinetics is a collection of processes for manipulating bulk fluid mass and embedded objects with AC electric fields. The ability of AC electrokinetics to implement the major microfluidic operations, such as pumping, mixing, concentration, and separation, makes it possible to develop integrated systems for clinical diagnostics in nontraditional health care settings. The high conductivity of physiological fluids presents new challenges and opportunities for AC electrokinetics-based diagnostic systems. In this review, AC electrokinetic phenomena in conductive physiological fluids are described followed by a review of the basic microfluidic operations and the recent biomedical applications of AC electrokinetics. The future prospects of AC electrokinetics for clinical diagnostics are presented.

Alternating current electrokinetics enhanced in situ capacitive immunoassay.

A rapid in situ capacitive immunoassay is presented herein. Conventional immunoassay typically relies on diffusion for transport of analytes in many cases causing long detection time and lack of sensitivity. By integrating alternating current electrokinetics (ACEK) and impedance sensing, this work provides a rapid in situ capacitive affinity biosensing. ACEK induces both fluid flow and particle motion, conveying target molecules toward electrodes immobilized with probes, resulting in rapid enrichment of target molecules and a capacitance change at the ''electrode-fluid'' interface. The benefit of ACEK enhanced immunoassay was demonstrated using the antigen and antibody from Johne's disease (JD) as an example. To clarify the importance of DEP and ACET effects for binding reaction, two different electrode pattern designs for capacitive immunoassay are studied. The asymmetric array and symmetric electrodes exhibit very similar response at lower electric field due to DEP effects, while asymmetric array has remarkable higher response at high-electric field because the convection becomes more important at high field. The disease positive and negative serum samples are distinguished in few minutes.

Comprehensive analysis of human cells motion under an irrotational AC electric field in an electro-microfluidic chip.

AC electrokinetics is a versatile tool for contact-less manipulation or characterization of cells and has been widely used for separation based on genotype translation to electrical phenotypes. Cells responses to an AC electric field result in a complex combination of electrokinetic phenomena, mainly dielectrophoresis and electrohydrodynamic forces. Human cells behaviors to AC electrokinetics remain unclear over a large frequency spectrum as illustrated by the self-rotation effect observed recently. We here report and analyze human cells behaviors in different conditions of medium conductivity, electric field frequency and magnitude. We also observe the self-rotation of human cells, in the absence of a rotational electric field. Based on an analytical competitive model of electrokinetic forces, we propose an explanation of the cell self-rotation. These experimental results, coupled with our model, lead to the exploitation of the cell behaviors to measure the intrinsic dielectric properties of JURKAT, HEK and PC3 human cell lines.

Janus particle microshuttle: 1D directional self-propulsion modulated by AC electrical field

A catalytic Janus particle is capable of gaining energy from the surrounding fuel solution to drive itself to move continuously, which has an important impact in different fields, especially the field of micro-systems. However, the randomness of self-propulsion at the microscale restricts its use in practice. Achieving a directed self-propelled movement would greatly promote the application of the Janus particle. We proved experimentally that an AC electric field was an effective way to suppress Brownian motion and control the direction of self-propelled movement. The self-propulsion and dielectrophoretic response of a 2μm Janus particle were observed and the related basic data were collected. Interdigital electrodes, 20 μm in width, were energized in pulsed style to modulate the self-propulsion, which resulted in a shuttle-style motion in which a single Janus particle moved to and fro inside the strip electrode. The change of direction depends on its unique position: the catalyst side is always pointed outward and the orientation angle relative to the electrode is about 60°. Numerical simulation also proved that this position is reasonable. The present study could be beneficial with regard to self-propulsion and AC electrokinetics of the Janus particle.

AC electrokinetics-enhanced capacitive immunosensor for point-of-care serodiagnosis of infectious diseases

The current serological diagnostic method can be time consuming and labor intensive, which is not practical for on-site diagnosis and screening of infectious diseases. Capacitive bioaffinity detection using microelectrodes is considered as a promising label-free method for point-of-care diagnosis, though with challenges in sensitivity and the time “from sample to result.” With recent development in AC electrokinetics (ACEK), especially in dielectrophoresis (DEP), we are able to develop an ACEK enhanced capacitive bioaffinity sensing method to realize simple, fast and sensitive diagnosis from serum samples. The capacitive immunosensor presented here employs elevated AC potentials at a fixed frequency for impedimetric interrogation of the microelectrodes. According to prior work, such an AC signal is capable of inducing dielectrophoresis and other ACEK effects, so as to realize in-situ enrichment of macromolecules at microelectrodes and hence accelerated detection. Experimental study of the ACEK-enhanced capacitive sensing method was conducted, and the results corroborate our hypothesis. The capacitive sensing responses showed clear frequency dependence and voltage-level dependency, which supports the hypothesis that ACEK aids the antigen–antibody binding, and these dependencies were used to optimize our detection protocol. Our capacitive sensing method was shown to work with bovine sera to differentiate disease-positive samples from negative samples within 2min, while conventional immunoassay would require multiple processing steps and take hours to complete. The results showed high accuracy and sensitivity. The detection limit is found to reach 10ng/ml in 2min. The ACEK-enhanced capacitive immunosensor is a platform technology, and can be employed to detect any combination of probe (e.g. antigen) and analyte (e.g. serum antibody) in a small volume of bodily fluids.

Comprehensive analysis of alternating current electrokinetics induced motion of colloidal particles in a three-dimensional microfluidic chip

AC electrokinetics is becoming a strategic tool for lab-on-a-chip systems due to its versatility and its high level of integration. The ability to foreseen the behaviour of fluids and particles under non-uniform AC electric fields is important to allow new generations of devices. Though most of studies predicted motion of particles in co-planar electrodes configurations, we explore a pure 3-D AC electrokinetic effect that can open the way to enhance contact-less handling throughout the microchannel. By fabricating 3D microfluidic chips with a bi-layer electrodes configuration where electrodes are patterned on both sides of the microfluidic channel, we present a detailed study of the AC electrokinetic regimes that govern particles motion suspended in different host media subjected to a non-uniform AC electric field that spreads through the cross-section of the microchannel. We simulate and observe the motion of 1, 5, and 10 μm polystyrene particles relative to the electrodes and provide an insight on the competition between electro-hydrodynamical forces and dielectrophoresis. We demonstrate that using relevant electrode designs combined with the appropriate applied AC potential, particles can be handled in 3-D in the micro-channel at a single or a collective level in several medium conductivities. Both numerical simulations and experimental results provide a useful basis for future biological applications.

Investigation of various ac electrokinetics in a microniche system for cell separation

We investigate various AC electrokinetic (dielectrophoresis, electro-thermal and electro-osmosis) phenomena in a micro-niche system for negative-dielectrophoresis (n-dep) based cell separation. For that purpose, an experimental system is constructed. The system is comprised of a slit-type electrode array to apply voltage, a micro cam-scope to monitor cell movement, micro stages to adjust the focal length of the cam-scope properly, a function generator to apply voltage with various frequencies, and an illumination system. After the conductivity of the medium and the magnitude and frequency of the voltage are selected as experiment variables, cell movement is investigated. The ranges of each variable studied are 0.001 ∼ 0.2 S/m, 1 ∼ 7 Vpp, and 100 Hz ∼ 1 MHz respectively. For the target cells, k562 cells of a leukemia cell line were employed. In the experimental study, n-dep is most dominant over other electrokinetic phenomena with 5 Vpp of input voltage and in the range of 100 ∼ 500 kHz although the theoretical equation indicates that the higher voltage (7 Vpp) generates a higher n-dep force. This is because the higher voltage causes not only a higher n-dep force but also higher electro-thermal and electro-osmosis. Based on the obtained experimental results, we expect to establish a reliable n-dep force based cell sorting system in the near future.

Single Cell Antimicrobial Susceptibility Testing by Confined Microchannels and Electrokinetic Loading

Multidrug-resistant pathogens are an emerging global health problem. In addition to the need of developing new antibiotics in the pipeline, the ability to rapidly determine the antibiotic resistance profiles of bacteria represents one of the most crucial steps toward the management of infectious diseases and the prevention of multidrug-resistant pathogens. Here, we report a single cell antimicrobial susceptibility testing (AST) approach for rapid determination of the antibiotic resistance of bacterial pathogens. By confining individual bacteria in gas permeable microchannels with dimensions comparable to a single bacterium, the antibiotic resistance of the bacteria can be monitored in real-time at the single cell level. To facilitate the dynamic loading of the bacteria into the confined microchannels for observation, AC electrokinetics is demonstrated for capturing bacteria to defined locations in high-conductivity AST buffer. The electrokinetic technique achieves a loading efficiency of about 75% with a negligible effect on the bacterial growth rate. To optimize the protocol for single cell AST, the bacterial growth rate of individual bacteria under different antibiotic conditions has been determined systematically. The applicability of single cell AST is demonstrated by the rapid determination of the antimicrobial resistant profiles of uropathogenic clinical isolates in Mueller-Hinton media and in urine. The antibiotic resistance profiles of bacteria can be determined in less than 1 h compared to days in standard culture-based AST techniques.

Electrokinetic confinement of axonal growth for dynamically configurable neural networks

Axons in the developing nervous system are directed via guidance cues, whose expression varies both spatially and temporally, to create functional neural circuits. Existing methods to create patterns of neural connectivity in vitro use only static geometries, and are unable to dynamically alter the guidance cues imparted on the cells. We introduce the use of AC electrokinetics to dynamically control axonal growth in cultured rat hippocampal neurons. We find that the application of modest voltages at frequencies on the order of 10(5) Hz can cause developing axons to be stopped adjacent to the electrodes while axons away from the electric fields exhibit uninhibited growth. By switching electrodes on or off, we can reversibly inhibit or permit axon passage across the electrodes. Our models suggest that dielectrophoresis is the causative AC electrokinetic effect. We make use of our dynamic control over axon elongation to create an axon-diode via an axon-lock system that consists of a pair of electrode 'gates' that either permit or prevent axons from passing through. Finally, we developed a neural circuit consisting of three populations of neurons, separated by three axon-locks to demonstrate the assembly of a functional, engineered neural network. Action potential recordings demonstrate that the AC electrokinetic effect does not harm axons, and Ca(2+) imaging demonstrated the unidirectional nature of the synaptic connections. AC electrokinetic confinement of axonal growth has potential for creating configurable, directional neural networks.

Rapid generation and manipulation of microfluidic vortex flows induced by AC electrokinetics with optical illumination

We demonstrate a rapid generation of twin opposing microvortices (TOMVs) induced by non-uniform alternating current (AC) electric fields together with a laser beam on a patterned pair of indium tin oxide (ITO) electrodes. A fast and strong jet flow region between twin microvortices is also generated. Its pattern and direction, such as whether it is symmetric or asymmetric, are controlled mainly by the location of a single laser spot relative to the ITO electrodes. With two laser beams, two separate flows are superposed to give a new one. In situ generation and control of the TOMV flow are tested in suspensions of fluorescent polystyrene particles, as well as in milk emulsions. This technique has great potential for dynamically manipulating micro-fluid flows, functioning as a micro-pump or mixer.

A rapid electrochemical biosensor based on an AC electrokinetics enhanced immuno-reaction

Fluorescent labelling and chromogenic reactions that are commonly used in conventional immunoassays typically utilize diffusion dominated transport of analytes, which is limited by slow reaction rates and long detection times. By integrating alternating current (AC) electrokinetics and electrochemical impedance spectroscopy (EIS), we construct an immunochip for rapid, sensitive, and label-free detection. AC electroosmosis (ACEO) and positive dielectrophoresis (DEP), induced by a biased AC electric field, can rapidly convect and trap the analyte onto an EIS working electrode within a few minutes. This allows the change of electron-transfer resistance (ΔRet) caused by the antibody-antigen (IgG-protein A) binding to be measured and quantified in real time. The measured impedance change achieves a plateau after electrokinetic concentration for only 90 s, and the detection limit is able to reach 200 pg ml⁻¹. Compared to the conventional incubation method, the electrokinetics-enhanced method is approximately 100 times faster in its reaction time, and the detection limit is reduced by 30 times. The ΔRet of the positive response is two orders of magnitude higher than the negative control, demonstrating excellent specificity for practical applications.

An AC electrokinetics facilitated biosensor cassette for rapid pathogen identification

To develop a portable point-of-care system based on biosensors for common infectious diseases such as urinary tract infection, the sensing process needs to be implemented within an enclosed fluidic system. On chip sample preparation of clinical samples remains a significant obstacle to achieving robust sensor performance. Herein AC electrokinetics is applied in an electrochemical biosensor cassette to enhance molecular convection and hybridization efficiency through electrokinetics induced fluid motion and Joule heating induced temperature elevation. Using E. coli as an exemplary pathogen, we determined the optimal electrokinetic parameters for detecting bacterial 16S rRNA in the biosensor cassette based on the current output, signal-to-noise ratio, and limit of detection. In addition, a panel of six probe sets targeting common uropathogenic bacteria was demonstrated. The optimized parameters were also validated using patient-derived clinical urine samples. The effectiveness of electrokinetics for on chip sample preparation will facilitate the implementation of point-of-care diagnosis of urinary tract infection in the future.

Advancing practical usage of microtechnology: a study of the functional consequences of dielectrophoresis on neural stem cells

The integration of microscale engineering, microfluidics, and AC electrokinetics such as dielectrophoresis has generated novel microsystems that enable quantitative analysis of cellular phenotype, function, and physiology. These systems are increasingly being used to assess diverse cell types, such as stem cells, so it becomes critical to thoroughly evaluate whether the systems themselves impact cell function. For example, engineered microsystems have been utilized to investigate neural stem/progenitor cells (NSPCs), which are of interest due to their potential to treat CNS disease and injury. Analysis by dielectrophoresis (DEP) microsystems determined that unlabeled NSPCs with distinct fate potential have previously unrecognized distinguishing electrophysiological characteristics, suggesting that NSPCs could be isolated by DEP microsystems without the use of cell type specific labels. To gauge the potential impact of DEP sorting on NSPCs, we investigated whether electric field exposure of varying times affected survival, proliferation, or fate potential of NSPCs in suspension. We found short-term DEP exposure (1 min or less) had no effect on NSPC survival, proliferation, or fate potential revealed by differentiation. Moreover, NSPC proliferation (measured by DNA synthesis and cell cycle kinetics) and fate potential were not altered by any length of DEP exposure (up to 30 min). However, lengthy exposure (>5 min) to frequencies near the crossover frequency (50-100 kHz) led to decreased survival of NSPCs (maximum ∼30% cell loss after 30 min). Based on experimental observations and mathematical simulations of cells in suspension, we find that frequencies near the crossover frequency generate an induced transmembrane potential that results in cell swelling and rupture. This is in contrast to the case for adherent cells since negative DEP frequencies lower than the crossover frequency generate the highest induced transmembrane potential and damage for these cells. We clarify contrasting effects of DEP on adherent and suspended cells, which are related to the cell position within the electric field and the strength of the electric field at specific distances from the electrodes. Modeling of electrode configurations predicts optimal designs to induce cell movement by DEP while limiting the induced transmembrane potential. We find DEP electric fields are not harmful to stem cells in suspension at short exposure times, thus providing a basis for developing DEP-based applications for stem cells.

Abstract 1704: AC electrokinetic isolation of cell free high molecular weight DNA (CF-HMW DNA) from serum

Abstract Recent reports of CF-HMW DNA in a variety of diseases has led to interest in its use as a prognostic biomarker, a diagnostic or screening tool for cancer. Apoptotic DNA (<200bp) is present in the circulation of normal healthy individuals. In cancer, unregulated cell growth leads to uncontrolled cell death, or necrosis, which produces HMW DNA (>500bp) that is then trafficked into circulation. Dielectrophoresis, or DEP (movement of particles in a non-uniform AC electric field), based electrokinetic techniques have been used for protein biomarker screening, cell separation, and DNA manipulation. Using specific DEP frequencies, analytes are moved to known locations (high or low field region) based on their inherent dielectric properties. The process allows specific nano-sized particles to be highly concentrated into high field regions, while micron-size cells are held weakly in low field regions. With fluidic washing, cells can be removed while nano-sized particles are held in high field regions. This method can effectively act as a CF-HMW DNA enrichment process for biological fluids. Unfortunately, DEP does not work well in (high conductance) physiological buffers, requiring significant dilution of the sample and, as a result, the target analyte concentration. Here, we describe a novel AC electrokinetic (ACE) technique using a custom microelectrode array and AC parameters to isolate and analyze CF-HMW DNA from high conductance serum. DNA from normal serum samples and the A549 cell line were isolated using Qiagen kits to determine initial DNA quantities. Normal sera were spiked with A549 cell line DNA at concentrations from 0 to 500 ng/ml and subjected to a 20 minute ACE protocol. DNA isolation was visualized in situ using SYBR Green I fluorescence and then eluted for use in secondary analyses. Results showed minimal fluorescence from samples without spike whereas A549 DNA spiked samples showed concentration-dependent fluorescence on the microelectrodes. After elution, levels of DNA were quantitated using ALU-sequence based qPCR and K-ras mutational status was confirmed by ABI CastPCR. Future experiments will compare CF-HMW DNA levels from normal and cancer patients across a variety of solid tumors. The ACE technique enables rapid isolation and detection of CF-HMW DNA directly from biological fluids without prior sample prep and has broad utility for diagnosis and monitoring of cancer and other diseases in which CF-HMW DNA may be used as a marker. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1704. doi:1538-7445.AM2012-1704

Gold nano-particle-based thermal sensors fabricated using microspotting and DEP techniques

We show that pearl chains of gold nano-particles (Au NPs) are formed consistently between microelectrodes by combining microspotting and dielectrophoretic (DEP) techniques. Experimental results on various sized Au particles and DEP parameters, including voltage and frequency, are reported in this paper to explore the critical parameters in controlling the pearl chain formation (PCF) process between microelectrodes. PCF is observed from 10kHz to 5MHz for 100nm diameter Au NPs, and 100kHz to 10MHz for 10nm Au NPs. Variations in formation rate are detected when the applied voltage and particle size varies. At higher voltages, PCF occurs at a higher rate and the formation time decreases. The optimum frequency for Au NPs PCF shifts to a higher frequency region when the particle size decreases. Theoretical analysis is carried out by calculating the DEP force with AC electrokinetics to explain the observations at DEP frequencies ranging from 10Hz to 10MHz. Finally, Au NP chains formed between the microelectrodes are shown to vary in resistance consistent with predictions for a simplified model of an impinging jet system, indicating that these Au particle sensors could potentially be used to precisely measure localized temperatures and other localized thermal phenomena.

Recent Applications of AC Electrokinetics in Biomolecular Analysis on Microfluidic Devices

AC electrokinetics is a generic term that refers to an induced motion of particles and fluids under nonuniform AC electric fields. The AC electric fields are formed by application of AC voltages to microelectrodes, which can be easily integrated into microfluidic devices by standard microfabrication techniques. Moreover, the magnitude of the motion is large enough to control the mass transfer on the devices. These advantages are attractive for biomolecular analysis on the microfluidic devices, in which the characteristics of small space and microfluidics have been mainly employed. In this review, I describe recent applications of AC electrokinetics in biomolecular analysis on microfluidic devices. The applications include fluid pumping and mixing by AC electrokinetic flow, and manipulation of biomolecules such as DNA and proteins by various AC electrokinetic techniques. Future prospects for highly functional biomolecular analysis on microfluidic devices with the aid of AC electrokinetics are also discussed.

Trapping Single Cells: Comparison between Sandwiched Insulation with Back Contact (SIBC) and Planar Biochip

AC electrokinetics is one of many methods used to move particles in microfluidic channels. This paper presents single cell trapping efficacy using dielectrophoresis (DEP) force of two biochip designs; a planar biochip and the new sandwiched-insulation with back contact (SIBC) biochip. The new biochip, is structured on a glass slide, consists of microelectrode arrays patterned on top of Nickel-Chromium (NiCr) and Gold (Au) layers. Prior to the microelectrode patterning, a back contact layer of NiCr and Au was coated with SU-8 2005. Then, the SU-8 2005 or the insulation layer was patterned with arrays of microcavities. In contrast, the planar biochip consists of 2 layers; an SU-8 2005 insulation layer and NiCr and Au metal layers constructed on a Silicon Nitride (Si3N4) substrate. The electric field intensity results simulated using Comsol v3.5a software indicated that DEP force generated from the SIBC biochip are greater than the planar biochip design. Results from experiment with polystyrene microbeads and Ishikawa cancer cells also showed that the SIBC biochip has higher trapping efficiency than the planar biochip. These promising results indicate that the SIBC biochip is capable of trapping single cells and can be used to facilitate studies on intracellular activities using surface the replicating technique known as the Bioimprint technique.