Dielectrophoresis applications in biomedical field and future perspectives in biomedical technology

Dielectrophoresis (DEP) is a technique to manipulate trajectories of polarisable particles in nonuniform electric fields by utilizing unique dielectric properties. The manipulation of a cell using DEP has been demonstrated in various modes, thereby indicating potential applications in the biomedical field. In this review, recent DEP applications in the biomedical field are discussed. This review is intended to highlight research work that shows significant approach related to DEP application in biomedical field reported between 2016 and 2020. First, single-shell model and multiple-shell model of cells are introduced. Current device structures and recently introduced electrode patterns for DEP applications are discussed. Second, the biomedical uses of DEP in liquid biopsies, stem cell-based therapies, and diagnosis of infectious diseases due to bacteria and viruses are presented. Finally, the challenges in DEP research are discussed, and the reported solutions are explained. DEP's potential research directions are mentioned.     

基于介电电泳的微流控细胞分离芯片的研究进展

细胞分离技术是细胞分选和细胞种群纯化的重要手段,在生物、医学、农业、环境等许多领域都有重要的应用,是当前生化分析领域的国际研究热点。本文介绍了基于介电电泳的微流控细胞分离芯片的研究现状,阐述了介电电泳的工作原理,并依据细胞尺寸、电极形状、外加信号方式等影响细胞介电电泳的关键因素对不同类型的微流控细胞分离芯片进行了详细介绍,并对该技术的未来发展趋势做了展望。     

Review: Dielectrophoresis in cell characterization

Many cellular functions are affected by and thus can be characterized by a cell's electrophysiology. This has also been found to correspond to other biophysical parameters such as cell morphology and mechanical properties. Dielectrophoresis (DEP) is an electrostatic technique which can be used to examine cellular biophysical parameters through the measuring of single or multiple cell response to electric field induced forces. This label-free method offers many advantages in characterizing a cell population over conventional electrophysiology methods such as patch clamping; however, it has yet to see mainstream pharmacological application. Challenges such as the transdisciplinary nature of the field bridging engineering and the biological sciences, throughput, specificity as well as standardization are being addressed in current literature. This review focuses on the developments of DEP-based cell electrophysiological characterization where determining cellular properties such as membrane conductance and capacitance, and cytoplasmic conductivity are the primary motivation. A brief theoretical review, techniques for obtaining these cell parameters, as well as the resulting cell parameters and their applications are included in this review. This review aims to further support the development of DEP-based cell characterization as an important part of the future of DEP and electrophysiology research.     

介电电泳芯片及其在细胞分析中的应用

简要阐述了在交流和直流电压电场中,介电电泳(DEP)芯片进行细胞分离富集的机理.按照驱动电场的差异对DEP芯片进行了分类,分析和比较了DEP芯片微电极的叉指电极、抛物线电极、堡式电极、三维电极等典型结构.特别对近年来DEP芯片在单细胞分析、细胞分离与富集以及临床细胞分析中的应用进展进行了综述,并对其应用前景和发展方向进行了展望.     

Dielectrophoresis: a model to transport drugs directly into teeth

The article describes an innovative delivery system based on the principles of dielectrophoresis to transport drugs directly into site-specific intraoral targets. The hypothesis that a drug can be driven into tooth enamel during the application of an applied electrical potential difference was tested by the authors in in vitro studies comparing dielectrophoresis to diffusion to transport carbamide peroxide and fluoride. The studies showed that these agents can be transported directly into teeth using an alternating current (AC) electric field more effectively than diffusion. It was found that a 20-min bleaching treatment on human teeth with dielectrophoresis increased carbamide peroxide absorption by 104% and, on average, improved the change in shade guide unit 14 times from 0.6 SGU to 9 SGU. After applying a 1.23% acidulated phosphate fluoride gel to bovine incisors for 20 min by dielectrophoresis or diffusion, analysis with wavelength dispersive spectrometry determined that dielectrophoresis doubled fluoride uptake in the superficial layers compared to diffusion, and drove the fluoride significantly deeper into enamel with an uptake 600% higher than diffusion at 50 μm depth. Finally, dielectrophoresis promises to be a viable model that can potentially be used clinically to deliver other targeted drugs of variable molecular weight and structure.     

Dielectrophoretic characterization and separation of monocytes and macrophages using 3D carbon‐electrodes

Monocyte heterogeneity and its prevalence are revealed as indicator of several human diseases ranking from cardiovascular diseases to rheumatoid arthritis, chronic kidney diseases, autoimmune multiple sclerosis, and stroke injuries. When monocytes and macrophages are characterized and isolated with preserved genetic, phenotypic and functional properties, they can be used as label‐free biomarkers for precise diagnostics and treatment of various diseases. Here, the dielectrophoretic responses of the monocytes and macrophages were examined. We present 3D carbon‐electrode dielectrophoresis (carbon‐DEP) as a separation tool for U937 monocytes and U937 monocyte‐differentiated macrophages. The carbon‐electrodes advanced the usability and throughput of DEP separation, presented wider electrochemical stability. Using the 3D carbon‐DEP chip, we first identified the selective positive and negative DEP responses and specific crossover frequencies of monocytes and macrophages as their signatures for separation. The crossover frequency of monocytes and macrophages was 17 and 30 kHz, respectively. Next, we separated monocyte and macrophage subpopulations using their specific dielectrophoretic responses. Afterward, we used a fluorescence‐activated cell sorter to confirm our results. Finally, we enriched 70% of monocyte cells from the mixed cell population, in other words, concentration of monocyte cells to macrophage cells was five times increased, using the 30‐kHz, 10‐Vpp electric field and 1 μL/min flow rate.     

Dielectrophoresis with 3D microelectrodes fabricated by surface tension assisted lithography

This paper demonstrates the utilization of 3D semispherical shaped microelectrodes for dielectrophoretic manipulation of yeast cells. The semispherical microelectrodes are capable of producing strong electric field gradients, and in turn dielectrophoretic forces across a large area of channel cross‐section. The semispherical shape of microelectrodes avoids the formation of undesired sharp electric fields along the structure and also minimizes the disturbance of the streamlines of nearby passing fluid. The advantage of semispherical microelectrodes over the planar microelectrodes is demonstrated in a series of numerical simulations and proof‐of‐concept experiments aimed toward immobilization of viable yeast cells.     

Dielectrophoretic trapping of multilayer DNA origami nanostructures and DNA origami‐induced local destruction of silicon dioxide

DNA origami is a widely used method for fabrication of custom‐shaped nanostructures. However, to utilize such structures, one needs to controllably position them on nanoscale. Here we demonstrate how different types of 3D scaffolded multilayer origamis can be accurately anchored to lithographically fabricated nanoelectrodes on a silicon dioxide substrate by DEP. Straight brick‐like origami structures, constructed both in square (SQL) and honeycomb lattices, as well as curved “C”‐shaped and angular “L”‐shaped origamis were trapped with nanoscale precision and single‐structure accuracy. We show that the positioning and immobilization of all these structures can be realized with or without thiol‐linkers. In general, structural deformations of the origami during the DEP trapping are highly dependent on the shape and the construction of the structure. The SQL brick turned out to be the most robust structure under the high DEP forces, and accordingly, its single‐structure trapping yield was also highest. In addition, the electrical conductivity of single immobilized plain brick‐like structures was characterized. The electrical measurements revealed that the conductivity is negligible (insulating behavior). However, we observed that the trapping process of the SQL brick equipped with thiol‐linkers tended to induce an etched “nanocanyon” in the silicon dioxide substrate. The nanocanyon was formed exactly between the electrodes, that is, at the location of the DEP‐trapped origami. The results show that the demonstrated DEP‐trapping technique can be readily exploited in assembling and arranging complex multilayered origami geometries. In addition, DNA origamis could be utilized in DEP‐assisted deformation of the substrates onto which they are attached.     

Image‐based sorting and negative dielectrophoresis for high purity cell and particle separation

Microelectrode arrays are used to sort single fluorescently labeled cells and particles as they flow through a microfluidic channel using dielectrophoresis. Negative dielectrophoresis is used to create a “Dielectrophoretic virtual channel” that runs along the center of the microfluidic channel. By switching the polarity of the electrodes, the virtual channel can be dynamically reconfigured to direct particles along a different path. This is demonstrated by sorting particles into two microfluidic outlets, controlled by an automated system that interprets video data from a color camera and makes complex sorting decisions based on color, intensity, size, and shape. This enables the rejection of particle aggregates and other impurities, and the system is optimized to isolate high purity populations from a heterogeneous sample. Green beads are isolated from an excess of red beads with 100% purity at a rate of up to 0.9 particles per second, in addition application to the sorting of osteosarcoma and human bone marrow cells is evidenced. The extension of Dielectrophoretic Virtual Channels to an arbitrary number of sorting outputs is examined, with design, simulation, and experimental verification of two alternate geometries presented and compared.     

Particle trapping in electrically driven insulator-based microfluidics: Dielectrophoresis and induced-charge electrokinetics

Electrokinetically driven insulator-based microfluidic devices represent an attractive option to manipulate particle suspensions. These devices can filtrate, concentrate, separate, or characterize micro and nanoparticles of interest. Two decades ago, inspired by electrode-based dielectrophoresis, the concept of insulator-based dielectrophoresis (iDEP) was born. In these microfluidic devices, insulating structures (i.e., posts, membranes, obstacles, or constrictions) built within the channel are used to deform the spatial distribution of an externally generated electric field. As a result, particles suspended in solution experience dielectrophoresis (DEP). Since then, it has been assumed that DEP is responsible for particle trapping in these devices, regardless of the type of voltage being applied to generate the electric field—direct current (DC) or alternating current. Recent findings challenge this assumption by demonstrating particle trapping and even particle flow reversal in devices that prevent DEP from occurring (i.e., unobstructed long straight channels stimulated with a DC voltage and featuring a uniform electric field). The theory introduced to explain those unexpected observations was then applied to conventional “DC-iDEP” devices, demonstrating better prediction accuracy than that achieved with the conventional DEP-centered theory. This contribution summarizes contributions made during the last two decades, comparing both theories to explain particle trapping and highlighting challenges to address in the near future.     

Separation of malignant human breast cancer epithelial cells from healthy epithelial cells using an advanced dielectrophoresis-activated cell sorter (DACS)

In this paper, we successfully separated malignant human breast cancer epithelial cells (MCF 7) from healthy breast cells (MCF 10A) and analyzed the main parameters that influence the separation efficiency with an advanced dielectrophoresis (DEP)-activated cell sorter (DACS). Using the efficient DACS, the malignant cancer cells (MCF 7) were isolated successfully by noninvasive methods from normal cells with similar cell size distributions (MCF 10A), depending on differences between their material properties such as conductivity and permittivity, because our system was able to discern the subtle differences in the properties by generating continuously changed electrical field gradients. In order to evaluate the separation performance without considering size variations, the cells collected from each outlet were divided into size-dependent groups and counted statistically. Following that, the quantitative relative ratio of numbers between MCF 7 and MCF 10A cells in each size-dependent group separated by the DEP were compared according to applied frequencies in the range 48, 51, and 53 MHz with an applied amplitude of 8 V_pp. Finally, under the applied voltage of 48 MHz–8 V_pp and a flow rate of 290 μm/s, MCF 7 and MCF 10A cells were separated with a maximum efficiency of 86.67% and 98.73% respectively. Therefore, our suggested system shows it can be used for detection and separation of cancerous epithelial cells from noncancerous cells in clinical applications.     

基于芯片介电电泳的细胞特性分析及种类判断

基于微流控芯片介电电泳( Dielectrophoresis,DEP)原理和技术,在自行设计制作的抛物线电极结构的微流控介电电泳芯片上,采用芯片介电泳临界频率测定法,选择缓冲液电导率为200～1000 μS/cm,激发电压为5V,分别对红细胞(RBC)、白细胞(WBC)和死活HepG2肝癌细胞的临界频率进行了测试,检测...     

碳纳米管介电电泳精确及可控组装技术

碳纳米管(CNTs)具有优良的电学、热学、光学、力学性能和大的长径比,使得碳纳米管在能源存储、生物医药学、催化剂载体、水气过滤、复合材料等领域存在极大的应用价值。碳纳米管在金属电极之间的精确可控组装是实现其诸多应用的前提,介电电泳法是目前最常用且最具前景的组装方法之一。文中介绍了介电电泳法组装碳纳米管的原理,分析了介电电泳组装碳纳米管的影响因素,分别从碳纳米管的精确定位组装和数量可控组装两个方面进行了综述。     

Dielectrophoresis assisted immuno-capture and detection of foodborne pathogenic bacteria in biochips

This study integrated dielectrophoresis (DEP) with non-flow through biochips to enhance the immuno-capture and detection of foodborne pathogenic bacteria. It demonstrated two major functions provided by DEP to improve the chip performance: (i) concentrating bacterial cells from the suspension to different locations on the chip surface by positive and negative DEP; (ii) making the cells in close contact with the immobilized antibodies on the chip surface so that immuno-capture efficiency can be dramatically enhanced.The microchip achieved the immuno-capture efficiencies of ∼56.0% and ∼64.0% to Salmonella cells with 15 and 30 min DEP, respectively, which were considerably higher than those of ∼10.4% and ∼17.6% for 15 and 30 min immuno-capture without DEP. The immuno-captured bacterial cells were detected by the sandwich format ELISA on the chips. The final absorbance signals were enhanced by DEP assisted immuno-capture by 64.7-105.2% for the samples containing 10³-10⁶ cells/20 μl. The integration of DEP with the biochips has the potential to advance the chip-based immunoassay methods for microbial detection.     

A Review of Multifunctions of Dielectrophoresis in Biosensors and Biochips for Bacteria Detection

This paper reviews the functions of dielectrophoresis (DEP) that have been applied to biosensor and biochip platforms for bacteria detection, including concentration of bacterial cells from continuous flows, separation of target bacterial cells from non-target cells, as well as the enhancement of antibody capture efficiency on biosensor and biochip surfaces. DEP could provide effective concentration and separation simultaneously in well-designed microfluidic biosensor and biochip systems. The integration of DEP with a detection system allows the integration of sample preparation and enrichment steps with detection, which has the potential to eliminate the traditionally used time-consuming culture-based enrichment steps and other multiple off-chip sample preparation steps. DEP is also useful in biosensor and biochips platforms for enhancing antibody capture efficiency in both flow-through and non-flow-through microdevices. The enhanced antibody capture efficiency could allow the sensor capture more cells and to be detected by the sensor, particularly in dealing with low number of cells. The integration of multifunctions of DEP into biosensor and biochip platform has the potential to improve the detection of bacterial cells.     

A novel ultralow conductivity electromanipulation buffer improves cell viability and enhances dielectrophoretic consistency

Cell separation has become a critical diagnostic, research, and treatment tool for personalized medicine. Despite significant advances in cell separation, most widely used applications require the use of multiple, expensive antibodies to known markers in order to identify subpopulations of cells for separation. Dielectrophoresis (DEP) provides a biophysical separation technique that can target cell subpopulations based on phenotype without labels and return native cells for downstream analysis. One challenge in employing any DEP device is the sample being separated must be transferred into an ultralow conductivity medium, which can be detrimental in retaining cells’ native phenotypes for separation. Here, we measured properties of traditional DEP reagents and determined that after just 1–2 h of exposure and subsequent culture, cells’ viability was significantly reduced below 50%. We developed and tested a novel buffer (Cyto Buffer) that achieved 6 weeks of stable shelf-life and demonstrated significantly improved viability and physiological properties. We then determined the impact of Cyto Buffer on cells’ dielectric properties and morphology and found that cells retained properties more similar to that of their native media. Finally, we vetted Cyto Buffer's usability on a cell separation platform (Cyto R1) to determine combined efficacy for cell separations. Here, more than 80% of cells from different cell lines were recovered and were determined to be >70% viable following exposure to Cyto Buffer, flow stimulation, electromanipulation, and downstream collection and growth. The developed buffer demonstrated improved opportunities for electrical cell manipulation, enrichment, and recovery for next generation cell separations.     

Dielectrophoretic field‐flow fractionation of electroporated cells

We describe the development and testing of a setup that allows for DEP field‐flow fractionation (DEP‐FFF) of irreversibly electroporated, reversibly electroporated, and nonelectroporated cells based on their different polarizabilities. We first optimized the channel and electrode dimensions, flow rate, and electric field parameters for efficient DEP‐FFF separation of moderately heat‐treated CHO cells (50°C for 15 min) from untreated ones, with the former used as a uniform and stable model of electroporated cells. We then used CHO cells exposed to electric field pulses with amplitudes from 1200 to 2800 V/cm, yielding six groups containing various fractions of nonporated, reversibly porated, and irreversibly porated cells, testing their fractionation in the chamber. DEP‐FFF at 65 kHz resulted in distinctive flow rates for nonporated and each of the porated cell groups. At lower frequencies, the efficiency of fractionation deteriorated, while at higher frequencies the separation of individual elution profiles was further improved, but at the cost of cell flow rate slowdown in all the cell groups, implying undesired transition from negative into positive DEP, where the cells are pulled toward the electrodes. Our results demonstrate that fractionation of irreversibly electroporated, reversibly electroporated, and nonelectroporated cells is feasible at a properly selected frequency.     

A review: Dielectrophoresis for characterizing and separating similar cell subpopulations based on bioelectric property changes due to disease progression and therapy assessment

This paper reviews the use of dielectrophoresis for high-fidelity separations and characterizations of subpopulations to highlight the recent advances in the electrokinetic field as well as provide insight into its progress toward commercialization. The role of cell subpopulations in heterogeneous clinical samples has been studied to deduce their role in disease progression and therapy resistance for instances such as cancer, tissue regeneration, and bacterial infection. Dielectrophoresis (DEP), a label-free electrokinetic technique, has been used to characterize and separate target subpopulations from mixed samples to determine disease severity, cell stemness, and drug efficacy. Despite its high sensitivity to characterize similar or related cells based on their differing bioelectric signatures, DEP has been slowly adopted both commercially and clinically. This review addresses the use of dielectrophoresis for the identification of target cell subtypes in stem cells, cancer cells, blood cells, and bacterial cells dependent on cell state and therapy exposure and addresses commercialization efforts in light of its sensitivity and future perspectives of the technology, both commercially and academically.     

Microparticles manipulation and enhancement of their separation in pinched flow fractionation by insulator‐based dielectrophoresis

The separation and manipulation of microparticles in lab on a chip devices have importance in point of care diagnostic tools and analytical applications. The separation and sorting of particles from biological and clinical samples can be performed using active and passive techniques. In passive techniques, no external force is applied while in active techniques by applying external force (e.g. electrical), higher separation efficiency is obtained. In this article, passive (pinched flow fractionation) and active (insulator‐based dielectrophoresis) methods were combined to increase the separation efficiency at lower voltages. First by simulation, appropriate values of geometry and applied voltages for better focusing, separation, and lower Joule heating were obtained. Separation of 1.5 and 6 μm polystyrene microparticles was experimentally obtained at optimized geometry and low total applied voltage (25 V). Also, the trajectory of 1.5 μm microparticles was controlled by adjusting the total applied voltage.     

Dielectrophoretic deformation of breast cancer cells for lab on a chip applications

This paper presents the development and experimental analysis of a curved microelectrode platform for the DEP deformation of breast cancer cells (MDA‐MB‐231). The platform is composed of arrays of curved DEP microelectrodes which are patterned onto a glass slide and samples containing MDA‐MB‐231 cells are pipetted onto the platform's surface. Finite element method is utilised to characterise the electric field gradient and DEP field. The performance of the system is assessed with MDA‐MB‐231 cells in a low conductivity 1% DMEM suspending medium. We applied sinusoidal wave AC potential at peak to peak voltages of 2, 5, and 10 V_pp at both 10 kHz and 50 MHz. We observed cell blebbing and cell shrinkage and analyzed the percentage of shrinkage of the cells. The experiments demonstrated higher percentage of cell shrinkage when cells are exposed to higher frequency and peak to peak voltage electric field.