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1. Fine-Tuning Electrokinetic Injections Considering Nonlinear Electrokinetic Effects in Insulator-Based Devices

   https://doi.org/10.3390/mi12060628  

   Miller, Abbi; Hill, Nicole; Hakim, Kel; Lapizco-Encinas, Blanca H. (June 2021, Micromachines)

   null (Ed.)

   The manner of sample injection is critical in microscale electrokinetic (EK) separations, as the resolution of a separation greatly depends on sample quality and how the sample is introduced into the system. There is a significant wealth of knowledge on the development of EK injection methodologies that range from simple and straightforward approaches to sophisticated schemes. The present study focused on the development of optimized EK sample injection schemes for direct current insulator-based EK (DC-iEK) systems. These are microchannels that contain arrays of insulating structures; the presence of these structures creates a nonuniform electric field distribution when a potential is applied, resulting in enhanced nonlinear EK effects. Recently, it was reported that the nonlinear EK effect of electrophoresis of the second kind plays a major role in particle migration in DC-iEK systems. This study presents a methodology for designing EK sample injection schemes that consider the nonlinear EK effects exerted on the particles being injected. Mathematical modeling with COMSOL Multiphysics was employed to identify proper voltages to be used during the EK injection process. Then, a T-microchannel with insulating posts was employed to experimentally perform EK injection and separate a sample containing two types of similar polystyrene particles. The quality of the EK injections was assessed by comparing the resolution (Rs) and number of plates (N) of the experimental particle separations. The findings of this study establish the importance of considering nonlinear EK effects when planning for successful EK injection schemes. 

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2. Dielectrophoresis in Carcinoma Diagnosis: Recent Developments and Applications

   https://doi.org/10.1002/elps.8127  

   Vaghef‐Koodehi, Alaleh; Lapizco‐Encinas, Blanca H (August 2025, ELECTROPHORESIS)

   ABSTRACT Accurate cancer cell analysis is critical across a wide range of medical fields, including clinical diagnostics, personalized medicine, drug development, and cancer research. The ability to rapidly analyze and characterize cancer cells is key to understanding tumor characteristics, developing targeted therapies, and improving patient outcomes. Microscale electrokinetic (EK) techniques have demonstrated their effectiveness and reliability as powerful tools for cell analysis, including cancerous cells. The applications of dielectrophoresis (DEP), an EK technique, in cancer cell analysis are discussed here with a focus on carcinomas, cancer that develops in epithelial tissue. In this review article, the working mechanism of DEP is first introduced, followed by an in‐depth review of recent studies published between 2015 and 2024. The concluding remarks section provides a summary of the key points discussed in this review and offers insights into potential future advancements in DEP‐based systems for analyzing cancerous cells. 

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3. Determination of the Empirical Electrokinetic Equilibrium Condition of Microorganisms in Microfluidic Devices

   https://doi.org/10.3390/bios10100148  

   Coll De Peña, Adriana; Hill, Nicole; Lapizco-Encinas, Blanca H. (October 2020, Biosensors)

   null (Ed.)

   The increased concern regarding emerging pathogens and antibiotic resistance has drawn interest in the development of rapid and robust microfluidic techniques to analyze microorganisms. The novel parameter known as the electrokinetic equilibrium condition (EEEC) was presented in recent studies, providing an approach to analyze microparticles in microchannels employing unique electrokinetic (EK) signatures. While the EEEC shows great promise, current estimation approaches can be time-consuming or heavily user-dependent for accurate values. The present contribution aims to analyze existing approaches for estimating this parameter and modify the process into an accurate yet simple technique for estimating the EK behavior of microorganisms in insulator-based microfluidic devices. The technique presented here yields the parameter called the empirical electrokinetic equilibrium condition (eEEEC) which works well as a value for initial approximations of trapping conditions in insulator-based EK (iEK) microfluidic systems. A total of six types of microorganisms were analyzed in this study (three bacteria and three bacteriophages). The proposed approach estimated eEEEC values employing images of trapped microorganisms, yielding high reproducibility (SD 5.0–8.8%). Furthermore, stable trapping voltages (sTVs) were estimated from eEEEC values for distinct channel designs to test that this parameter is system-independent and good agreement was obtained when comparing estimated sTVs vs. experimental values (SD 0.3–19.6%). The encouraging results from this work were used to generate an EK library of data, available on our laboratory website. The data in this library can be used to design tailored iEK microfluidic devices for the analysis of microorganisms. 

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4. Numerical Simulation Noise and Its Significant Impact on the Dielectrophoretic Motion of Particles Near the Electrode Edges

   https://doi.org/10.1002/elps.8115  

   Bangaru, Aaditya_Venkatesha Babu; Williams, Stuart J (February 2025, ELECTROPHORESIS)

   ABSTRACT Dielectrophoresis (DEP) has been extensively researched over the years for filtration, separation, detection, and collection of micro/nano/bioparticles. Numerical models have historically been employed to predict particle trajectories in three‐dimensional (3D) DEP systems, but a common issue arises due to inherent noise near the edges of electrodes due to electric potential discontinuity, specifically when calculating electric field and gradient of electric field‐squared, . This noise can be reduced to a certain extent with a finer mesh density but results near the electrode edge still have significant error. Realizing the importance of particle‐electrode edge interactions prevalent in positive DEP systems, analytical solutions given by Sun et al. was incorporated to demonstrate an improved 3D model of interdigitated electrodes. The results of electric field and gradient of electric field‐squared of the numerical model and the improved analytical 3D model were compared, within a simulation space of 50 µm height, 10 µm width, and 50 µm length with interdigitated electrodes of the same width and gap of 10 µm. The DEP particle trajectory error due to the noise was quantified for different particle sizes at various heights above the electrode edge. For example, at 5 V_rms, a trapped 500 nm particles exhibited a velocity error of 10⁴µm/s (it should have been zero). 

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5. Dielectrophoretic trapping of particles flowing through an array of conductive cylinders

   https://doi.org/10.1063/5.0305604  

   Mondal, Tonoy K; Williams, Stuart J (December 2025, Physics of Fluids)

   Dielectrophoresis (DEP) is a label-free electrokinetic method for selectively trapping polarizable particles using non-uniform electric fields. While co-planar electrode systems are common, their inherent DEP force distribution limits throughput. This study presents a computationally efficient framework for modeling two-dimensional DEP-based particle trapping in ordered arrays of conductive cylinders. These cylinders are modeled at a range of sizes, from micrometers to nanometers, to represent microfluidic systems consisting of conductive pillars, nanofibers, etc. Analytical solutions for fluid flow and electric potential were derived using eigenfunction expansions and collocation, then used in a particle tracking model that includes hydrodynamic drag, Brownian motion, and multipolar DEP forces. Although focused on conductive arrays, this framework is extensible to other configurations. This work provides a foundation for future work in the design of high-throughput DEP systems. Both dimensionless and dimensional analyses were performed across a wide range of particle sizes (30 nm to 3 μm), voltages (10 mV to 100 V), and array geometries. No specific optimal cylinder size was found; instead, optimal performance arises from a balance between DEP force distribution and flow through the cylinder array gap. Diamond-oriented arrays exhibited enhanced trapping under moderate dielectrophoretic velocity-to-fluid velocity ratios (up to 39% greater), while square arrays performed better under low-field and large-cylinder conditions (up to 40% greater). 

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