Dielectrophoretic detection of electrical property changes of stored human red blood cells

The ability to transport and store a large human blood inventory for transfusions is an essential requirement for medical institutions. Thus, there is an important need for rapid and low-cost characterization tools for analyzing the properties of human red blood cells (RBCs) while in storage. In this study, we investigate the ability to use dielectrophoresis (DEP) for measuring the storage-induced changes in RBC electrical properties. Fresh human blood was collected, suspended in K2-EDTA anticoagulant, and stored in a blood bank refrigerator for a period of 20 days. Cells were removed from storage at 5-day intervals and subjected to a glutaraldehyde crosslinking reaction to “freeze” cells at their ionic equilibrium at that point in time and prevent ion leakage during DEP analysis. The DEP behavior of RBCs was analyzed in a high permittivity DEP buffer using a three-dimensional DEP chip (3DEP) and also compared to measurements taken with a 2D quadrupole electrode array. The DEP analysis confirms that RBC electrical property changes occur during storage and are only discernable with the use of the cell crosslinking reaction above a glutaraldehyde fixation concentration of 1.0 w/v%. In particular, cytoplasm conductivity was observed to decrease by more than 75% while the RBC membrane conductance was observed to increase by more than 1000% over a period of 20 days. These results show that the presented combination of chemical crosslinking and DEP can be used as rapid characterization tool for monitoring electrical properties changes of human RBCs while subjected to refrigeration in blood bank storage.     

The electrodynamics of rod-like microparticles based on optically induced dielectrophoresis

Due to its characteristics of noncontact, non-damage, high flux, and easy-to-achieve flexible manipulation, optically induced dielectrophoresis (ODEP) technology has been employed to manipulate microspherical biological particles, including separation, enrichment, capture, arrangement, and fusion. However, in nature, biomolecules are morphologically diverse, and some of them are rodlike. In order to illustrate the electrodynamics of rodlike particles under the action of ODEP, a transient multi-physical field coupling model of ODEP chip under the hypothesis of electrical double layer thin layer was established in this paper. The arbitrary Lagrangian–Eulerian method is used to track single-rod particle in the strong coupled flow field and electric field simultaneously. The influence of several key factors, including the applied alternating current (AC) electric voltage, the width of optical bright area, and the initial position of particle, on the trajectory of particle center was analyzed in positive dielectrophoresis (DEP) action and negative DEP action, respectively. Especially, the planar motion process of rodlike particles was discussed together. The research results reveal the electrodynamics behavior of rodlike particles based on the action of ODEP, which may provide theoretical support for the further design of rodlike biological cells manipulation chip based on AC ODEP technology in the future.     

Trapping and releasing of single microparticles and cells in a microfluidic chip

A microfluidic device was designed and fabricated to capture single microparticles and cells by using hydrodynamic force and selectively release the microparticles and cells of interest via negative dielectrophoresis by activating selected individual microelectrodes. The trap microstructure was optimized based on numerical simulation of the electric field as well as the flow field. The capture and selective release functions of the device were verified by multi-types microparticles with different diameters and K562 cells. The capture efficiencies/release efficiencies were 95.55% ± 0.43%/96.41% ± 1.08% and 91.34% ± 0.01%/93.67% ± 0.36% for microparticles and cells, respectively. By including more traps and microelectrodes, the device can achieve high throughput and realize the visual separation of microparticles/cells of interest in a large number of particle/cell groups.     

Rapid determination of NSAIDs by capillary and microchip electrophoresis with capacitively coupled contactless conductivity detection in wastewater

A simple, rapid method using CE and microchip electrophoresis with C⁴D has been developed for the separation of four nonsteroidal anti-inflammatory drugs (NSAIDs) in the environmental sample. The investigated compounds were ibuprofen (IB), ketoprofen (KET), acetylsalicylic acid (ASA), and diclofenac sodium (DIC). In the present study, we applied for the first time microchip electrophoresis with C⁴D detection to the separation and detection of ASA, IB, DIC, and KET in the wastewater matrix. Under optimum conditions, the four NSAIDs compounds could be well separated in less than 1 min in a BGE composed of 20 mM His/15 mM Tris, pH 8.6, 2 mM hydroxypropyl-beta-cyclodextrin, and 10% methanol (v/v) at a separation voltage of 1000–1200 V. The proposed method showed excellent repeatability, good sensitivity (LODs ranging between 0.156 and 0.6 mg/L), low cost, high sample throughputs, portable instrumentation for mobile deployment, and extremely lower reagent and sample consumption. The developed method was applied to the analysis of pharmaceuticals in wastewater samples with satisfactory recoveries ranging from 62.5% to 118%.     

Analysis of U87 glioma cells by dielectrophoresis

Glioblastoma multiforme is the most aggressive and invasive brain cancer consisting of genetically and phenotypically altering glial cells. It has massive heterogeneity due to its highly complex and dynamic microenvironment. Here, electrophysiological properties of U87 human glioma cell line were measured based on a dielectrophoresis phenomenon to quantify the population heterogeneity of glioma cells. Dielectrophoretic forces were generated using a gold-microelectrode array within a microfluidic channel when 3 V_pp and 100, 200, 300, 400, 500 kHz, 1, 2, 5, and 10 MHz frequencies were applied. We analyzed the dielectrophoretic behavior of 500 glioma cells, and revealed that the crossover frequency of glioma cells was around 140 kHz. A quantifying dielectrophoretic movement of the glioma cells exhibited three distinct glioma subpopulations: 50% of the glioma cells experienced strong, 30% of the cells were spread in the microchannel by moderate, and the rest of the cells experienced very weak positive dielectrophoretic forces. Our results demonstrated the dielectrophoretic spectra of U87 glioma cell line. Dielectrophoretic responses of glioma cells linked population heterogeneity to membrane properties of glioma cells rather than their size distribution in the population.     

Fast determination of paracetamol and its hydrolytic degradation product p-aminophenol by capillary and microchip electrophoresis with contactless conductivity detection

Paracetamol (PAC) is one of the most extensively used analgesics and antipyretic drugs to treat mild and moderate pain. P-aminophenol (PAP), the main hydrolytic degradation product of PAC, can be found in environmental water. Recently, CE has been developed for the detection of a wide variety of chemical substances. The purpose of this study is to develop a simple and fast method for the detection and separation of PAC and its main hydrolysis product PAP using CE and microchip electrophoresis with capacitively coupled contactless conductivity detection. The determination of these compounds using microchip electrophoresis with capacitively coupled contactless conductivity detection is being reported for the first time. The separation was run for all analytes using a BGE (20 mM β-alanine, pH 11) containing 14% (v/v) methanol. The RSDs obtained for migration time were less than 4%, and RSDs obtained for peak area were less than 7%. The detection limits (S/N = 3) that were achieved ranged from 0.3 to 0.6 mg/L without sample preconcentration. The presented method showed rapid analysis time (less than 1 min), high efficiency and precision, low cost, and a significant decrease in the consumption of reagents. The microchip system has proved to be an excellent analytical technique for fast and reliable environmental applications.     

A discrete dielectrophoresis device for the separation of malaria-infected cells

Malaria is a serious disease caused by Plasmodium parasites that infect red blood cells (RBCs). This paper presents the continuous separation of malaria-infected RBCs (iRBCs) from normal blood cells. The proposed method employed the discrete dielectrophoresis (DEP) in a microfluidic device with interdigitated electrodes. Our aim is to treat a sample having high concentration of cells to realize high throughput and to prevent the clogging of the microchannel with the use of the discrete DEP. The discrete DEP force for deflecting cells in the device was controlled by adjusting the magnitude, frequency, and duty cycle of the applied voltage. The effectiveness of the proposed method was demonstrated by separating the malaria-infected cells in samples having a cell concentration of 10⁶ cells/µl. From experimental results, we determined the enrichment that is needed to enhance the detection in the case of low parasitemia. The enrichment of the infected cells at the device output was 3000 times as high as that of the input containing 1 infected cell to 10⁶ normal cells. Therefore, the proposed method is highly effective and can significantly facilitate the detection of the infected cells for the identification of Malaria patients.     

DC-electrokinetic motion of colloidal cylinder(s) in the vicinity of a conducting wall

The boundary effects on DC-electrokinetic behavior of colloidal cylinder(s) in the vicinity of a conducting wall is investigated through a computational model. The contribution of the hydrodynamic drag, gravity, electrokinetic (i.e., electrophoretic and dielectrophoretic), and colloidal forces (i.e., forces due to the electrical double layer and van der Waals interactions) are incorporated in the model. The contribution of electrokinetic and colloidal forces are included by introducing the resulting forces as an external force acting on the particle(s). The colloidal forces are implemented with the prescribed expressions from the literature, and the electrokinetic force is obtained by integrating the corresponding Maxwell stress tensor over the particles' surfaces. The electrokinetic slip-velocity together with the thin electrical double layer assumption is applied on the surfaces. The position and velocity of the particles and the resulting electric and flow fields are obtained and the physical insight for the behavior of the colloidal cylinders are discussed in conjunction with the experimental observations in the literature.     

Dielectrophoretic motions of a single particle in the vicinity of a planar wall under a direct-current electric field

We have numerically investigated two-dimensional dielectrophoretic motions of one particle induced due to interactions with a nearby planar wall under uniform electric field. Results show that the motions depend strongly on the gap between the particle and wall and their conductivity combination while the motion direction is determined uniquely by the wall conductivity. The particle is repelled to move farther away from the wall less conductive than the fluid, and vice versa. The motions become strengthened as either conductivity of the particle or wall deviates further from that of the fluid. Finally, the mechanism for the wall-induced DEP motions is examined.