Recent advances in dielectrophoresis‐based cell viability assessment

Dielectrophoretic separation and purification: From colloid and biological particles to droplets

It is indispensable to realize the high level of purification and separation, so that objective particles, such as malignant cells, harmful bacteria, and special proteins or biological molecules, could satisfy the high precise measurement in the pharmaceutical analysis, clinical diagnosis, targeted therapy, and food defense. In addition, this could reveal the intrinsic nature and evolution mechanisms of individual biological variations. Consequently, many techniques related to optical tweezers, microfluidics, acoustophoresis, and electrokinetics can be broadly used to achieve micro- and nano-scale particle separations. Dielectrophoresis (DEP) has been used for various manipulation, concentration, transport, and separation processes of biological particles owing to its early development, mature theory, low cost, and high throughput. Although numerous reviews have discussed the biological applications of DEP techniques, comprehensive descriptions of micro- and nano-scale particle separations feature less frequently in the literature. Therefore, this review summarizes the current state of particle separation attention to relevant technological developments and innovation, including theoretical simulation, microchannel structure, electrode material, pattern and its layout. Moreover, a brief overview of separation applications using DEP in combination with other technologies is also provided. Finally, conclusions, future guidelines, and suggestions for potential promotion are highlighted.

A correlation of conductivity medium and bioparticle viability on dielectrophoresis-based biomedical applications

Dielectrophoresis (DEP) bioparticle research has progressed from micro to nano levels. It has proven to be a promising and powerful cell manipulation method with an accurate, quick, inexpensive, and label-free technique for therapeutic purposes. DEP, an electrokinetic phenomenon, induces particle movement as a result of polarization effects in a nonuniform electrical field. This review focuses on current research in the biomedical field that demonstrates a practical approach to DEP in terms of cell separation, trapping, discrimination, and enrichment under the influence of the conductive medium in correlation with bioparticle viability. The current review aims to provide readers with an in-depth knowledge of the fundamental theory and principles of the DEP technique, which is influenced by conductive medium and to identify and demonstrate the biomedical application areas. The high conductivity of physiological fluids presents obstacles and opportunities, followed by bioparticle viability in an electric field elaborated in detail. Finally, the drawbacks of DEP-based systems and the outlook for the future are addressed. This article will aid in advancing technology by bridging the gap between bioscience and engineering. We hope the insights presented in this review will improve cell suspension medium and promote DEP-viable bioparticle manipulation for health-care diagnostics and therapeutics.

Computer-Vision-Based Dielectrophoresis Mobility Tracking for Characterization of Single-Cell Biophysical Properties

Fast and precise measurements of live single-cell biophysical properties is significant in disease diagnosis, cytopathologic analysis, etc. Existing methods still suffer from unsatisfied measurement accuracy and low efficiency. We propose a computer vision method to track cell dielectrophoretic movements on a microchip, enabling efficient and accurate measurement of biophysical parameters of live single cells, including cell radius, cytoplasm conductivity, and cell-specific membrane capacitance, and in situ extraction of cell texture features. We propose a prediction-iteration method to optimize the cell parameter measurement, achieving high accuracy (less than 0.79% error) and high efficiency (less than 30 s). We further propose a hierarchical classifier based on a support vector machine and implement cell classification using acquired cell physical parameters and texture features, achieving high classification accuracies for identifying cell lines from different tissues, tumor and normal cells, different tumor cells, different leukemia cells, and tumor cells with different malignancies. The method is label-free and biocompatible, allowing further live cell studies on a chip, e.g., cell therapy, cell differentiation, etc.

Analysis of Temperature Field in the Dielectrophoresis-Based Microfluidic Cell Separation Device

Cell separation techniques based on dielectrophoresis are of high interest as an effective method of performing cell separation non-invasively on cells. However, dielectrophoresis devices have the problem that cells in the device are exposed to a high-temperature environment due to the generation of Joule heat caused by high-voltage application and dielectric-loss heat when the applied voltage is AC voltage. There is concern that the heat generated in the device may affect cell viability, cell cycle and apoptosis induction. In this study, the temperature field inside the dielectrophoretic cell separation device was experimentally and numerically investigated. The temperature rise at the bottom of the flow channel in the device was measured using the LIF method, and the thermofluidal behavior of the device was numerically simulated by adopting a heat generation model that takes the Joule and dielectric-loss heating into account in the energy equation. The temperature rise in the device was evaluated and the effect of the heat generation on cells in the device is discussed.

A dielectrophoresis-based microfluidic system having double-sided optimized 3D electrodes for label-free cancer cell separation with preserving cell viability

Early detection of circulating tumor cells (CTCs) in a patient's blood is essential to accurate prognosis and effective cancer treatment monitoring. The methods used to detect and separate CTCs should have a high recovery rate and ensure cells viability for post-processing operations, such as cell culture and genetic analysis. In this paper, a novel dielectrophoresis (DEP)-based microfluidic system is presented for separating MDA-MB-231 cancer cells from various subtypes of WBCs with the practical cell viability approach. Three configurations for the sidewall electrodes are investigated to evaluate the separation performance. The simulation results based on the finite-element method show that semi-circular electrodes have the best performance with a recovery rate of nearly 95% under the same operational and geometric conditions. In this configuration, the maximum applied electric field (1.11 × 10⁵ V/m) to separate MDA-MB-231 is lower than the threshold value for cell electroporation. Also, the Joule heating study in this configuration shows that the cells are not damaged in the fluid temperature gradient (equal to 1 K). We hope that such a complete and step-by-step design is suitable to achieve DEP-based applicable cell separation biochips.

Purification of pluripotent embryonic stem cells using dielectrophoresis and a flow control system

Pluripotent stem cells (PSCs) such as embryonic stem cells and induced PSCs can differentiate into all somatic cell types such as cardiomyocytes, nerve cells, and chondrocytes. However, PSCs can easily lose their pluripotency if the culture process is disturbed. Therefore, cell sorting methods for purifying PSCs with pluripotency are important for the establishment and expansion of PSCs. In this study, we focused on dielectrophoresis (DEP) to separate cells without fluorescent dyes or magnetic antibodies. The goal of this study was to establish a cell sorting method for the purification of PSCs based on their pluripotency using DEP and a flow control system. The dielectrophoretic properties of mouse embryonic stem cells (mESCs) with and without pluripotency were evaluated in detail, and mESCs exhibited varying frequency dependencies in the DEP response. Based on the variance in DEP properties, mixed cell suspensions of mESCs can be separated according to their pluripotency with an efficacy of approximately 90%.

Conductivity-difference-enhanced DC dielectrophoretic particle separation in a microfluidic chip

Conductivity-difference-enhanced DC dielectrophoretic particle separation in a microfluidic chip. Two immiscible electrolyte solutions with different conductivities in microchannels.

Surveilling cellular vital signs: toward label-free biosensors and real-time viability assays for bioprocessing

Cell viability is an essential facet of mammalian and microbial bioprocessing. While robust methods of monitoring cellular health remain critically important to biomanufacturing and biofabrication, the complexity of advanced cell culture platforms often poses challenges for conventional viability assays. This review surveys novel approaches to discern the metabolic, morphological, and mechanistic hallmarks of living systems - spanning subcellular and multicellular scales. While fluorescent probes coupled with 3D image analysis generate rapid results with spatiotemporal detail, molecular techniques like viability PCR can distinguish live cells with genetic specificity. Notably, label-free biosensors can detect nuanced attributes of cellular vital signs with single-cell resolution via optical, acoustic, and electrical signals. Ultimately, efforts to integrate these modalities with automation, machine learning, and high-throughput workflows will lead to exciting new vistas across the cell viability landscape.

Dielectrophoresis applications in biomedical field and future perspectives in biomedical technology

Dielectrophoresis (DEP) is a technique to manipulate trajectories of polarisable particles in non-uniform electric fields by utilising 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 dielectrophoresis application in biomedical field reported between 2016 and 2020. Firstly, single-shell model and multiple-shell model of cells are introduced. Current device structures and recently introduced electrode patterns for DEP applications are discussed. Secondly, the biomedical uses of DEP in liquid biopsies, stem cell 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. This article is protected by copyright. All rights reserved.

Label-Free Single Cell Viability Assay Using Laser Interference Microscopy

Laser interference microscopy (LIM) is a promising label-free method for single-cell research applicable to cell viability assessment in the studies of mammalian cells. This paper describes the development of a sensitive and reproducible method for assessing cell viability using LIM. The method, based on associated signal processing techniques, has been developed as a result of real-time investigation in phase thickness fluctuations of viable and non-viable MCF-7 cells, reflecting the presence and absence of their metabolic activity. As evinced by the values of the variable vc, this variable determines the viability of a cell only in the attached state (vc exceeds 20 nm2 for viable attached cells). The critical value of the power spectrum slope βc of the phase thickness fluctuations equals 1.00 for attached MCF-7 cells and 0.71 for suspended cells. The slope of the phase fluctuations' power spectrum for MCF-7 cells was determined to exceed the threshold value of βc for a living cell, otherwise the cell is dead. The results evince the power spectrum slope as the most appropriate indicator of cell viability, while the integrated evaluation criterion (vc and βc values) can be used to assay the viability of attached cells.

On the design, functions, and biomedical applications of high-throughput dielectrophoretic micro-/nanoplatforms: a review

As an efficient, rapid and label-free micro-/nanoparticle separation technique, dielectrophoresis (DEP) has attracted widespread attention in recent years, especially in the field of biomedicine, which exhibits huge potential in biomedically relevant applications such as disease diagnosis, cancer cell screening, biosensing, and others. DEP technology has been greatly developed recently from the low-flux laboratory level to high-throughput practical applications. In this review, we summarize the recent progress of DEP technology in biomedical applications, including firstly the design of various types and materials of DEP electrode and flow channel, design of input signals, and other improved designs. Then, functional tailoring of DEP systems with endowed specific functions including separation, purification, capture, enrichment and connection of biosamples, as well as the integration of multifunctions, are demonstrated. After that, representative DEP biomedical application examples in aspects of disease detection, drug synthesis and screening, biosensing and cell positioning are presented. Finally, limitations of existing DEP platforms on biomedical application are discussed, in which emphasis is given to the impact of other electrodynamic effects such as electrophoresis (EP), electroosmosis (EO) and electrothermal (ET) effects on DEP efficiency. This article aims to provide new ideas for the design of novel DEP micro-/nanoplatforms with desirable high throughput toward application in the biomedical community.

Dielectrophoresis as a tool for electrophysiological characterization of stem cells

Dielectrophoresis (DEP), a nonlinear electrokinetic technique caused by Maxwell-Wagner interfacial polarization of neutral particles in an electrolyte solution, is a powerful cell manipulation method used widely for various applications such as enrichment, trapping, and sorting of heterogeneous cell populations. While conventional cell characterization and sorting methods require tagging or labeling of cells, DEP has the potential to manipulate cells in a label-free way. Due to its unique ability to characterize and sort cells without the need of labeling, there is renewed interest in using DEP for stem cell research and regenerative medicine. Stem cells have the potential to differentiate into various lineages, but achieving homogeneous cell phenotypes from an initially heterogeneous cell population is a challenge. Using DEP to efficiently and affordably identify, sort, and enrich either undifferentiated or differentiated stem cell populations in a label-free way would advance their potential uses for applications in tissue engineering and regenerative medicine. This review summarizes recent, significant research findings regarding the electrophysiological characterization of stem cells, with a focus on cellular dielectric properties, i.e., permittivity and conductivity, and on studies that have obtained these measurements using techniques that preserve cell viability, such as crossover frequency. Potential applications for DEP in regenerative medicine are also discussed. Overall, DEP is a promising technique and, when used to characterize, sort, and enrich stem cells, will advance stem cell-based regenerative therapies.

Insulator Based Dielectrophoresis: Micro, Nano, and Molecular Scale Biological Applications

Insulator based dielectrophoresis (iDEP) is becoming increasingly important in emerging biomolecular applications, including particle purification, fractionation, and separation. Compared to conventional electrode-based dielectrophoresis (eDEP) techniques, iDEP has been demonstrated to have a higher degree of selectivity of biological samples while also being less biologically intrusive. Over the past two decades, substantial technological advances have been made, enabling iDEP to be applied from micro, to nano and molecular scales. Soft particles, including cell organelles, viruses, proteins, and nucleic acids, have been manipulated using iDEP, enabling the exploration of subnanometer biological interactions. Recent investigations using this technique have demonstrated a wide range of applications, including biomarker screening, protein folding analysis, and molecular sensing. Here, we review current state-of-art research on iDEP systems and highlight potential future work.

High-Sensitivity in Dielectrophoresis Separations

The applications of dielectrophoretic (DEP) techniques for the manipulation of cells in a label-free fashion within microfluidic systems continue to grow. However, a limited number of methods exist for making highly sensitive separations that can isolate subtle phenotypic differences within a population of cells. This paper explores efforts to leverage that most compelling aspect of DEP—an actuation force that depends on particle electrical properties—in the background of phenotypic variations in cell size. Several promising approaches, centering around the application of multiple electric fields with spatially mapped magnitude and/or frequencies, are expanding the capability of DEP cell separation.