Dielectric Properties Of Biological Cells Research Articles

Full Beta-Dispersion Region Dielectric Spectra and Dielectric Models of Viable and Non-Viable CHO Cells

The dielectric properties of biological cells can be used to gain information on their physiology and morphology. This paper reports the first measurements of the dielectric spectra of viable and non-viable cells over the full beta-dispersion (interfacial) frequency range. Dielectrophoresis (DEP) single cell in-flow techniques were employed to quantitatively measure the Clausius-Mossotti factor spectrum of individual cells over the 300 kHz–400 MHz range, covering both the MF and UHF DEP cross-over frequencies. Experiments were performed on Chinese hamster ovary (CHO) cells, one set cultured in growth media, the other in nutrient depleted media to induce apoptotic cells. Both cell states were measured using multi-frequency DEP flow cytometry, which provides the equivalent complex dielectric permittivity of individual cells. The measured dielectric spectra facilitate determination of a cell's morphology and the dielectric properties of its intracellular compartments, and are used to develop multi-shell dielectric models of viable and non-viable cells. The developed dielectric models can aid in biosensor design, in interpretation of bulk biomedia measurements where the heterogeneity in cell population can be masked, and in relating measured dielectric responses of cells to stimuli with changes in cellular physiology.

Dielectric properties of isolated adrenal chromaffin cells determined by microfluidic impedance spectroscopy

Knowledge of the dielectric properties of biological cells plays an important role in numerical models aimed at understanding how high intensity ultrashort nanosecond electric pulses affect the plasma membrane and the membranes of intracellular organelles. To this end, using electrical impedance spectroscopy, the dielectric properties of isolated, neuroendocrine adrenal chromaffin cells were obtained. Measured impedance data of the cell suspension, acquired between 1kHz and 20MHz, were fit into a combination of constant phase element and Cole-Cole models from which the effect of electrode polarization was extracted. The dielectric spectrum of each cell suspension was fit into a Maxwell-Wagner mixture model and the Clausius-Mossotti factor was obtained. Lastly, to extract the cellular dielectric parameters, the cell dielectric data were fit into a granular cell model representative of a chromaffin cell, which was based on the inclusion of secretory granules in the cytoplasm. Chromaffin cell parameters determined from this study were the cell and secretory granule membrane specific capacitance (1.22 and 7.10μF/cm2, respectively), the cytoplasmic conductivity, which excludes and includes the effect of intracellular membranous structures (1.14 and 0.49S/m, respectively), and the secretory granule milieu conductivity (0.35S/m). These measurements will be crucial for incorporating into numerical models aimed at understanding the differential poration effect of nanosecond electric pulses on chromaffin cell membranes.

Accuracy of the Maxwell–Wagner and the Bruggeman–Hanai mixture models for single cell dielectric spectroscopy

Dielectric spectroscopy (DS) is a non-invasive, label-free, and promising technique for measuring dielectric properties of biological cells. Recent developments in microfabrication techniques made it possible to perform DS measurements with minute volume of cell suspensions. However, when the cell size approaches the size of the measurement chamber, especially, for single cell measurements, the analytical models [Maxwell–Wagner and Bruggeman–Hanai (BH) mixture models] to extract cell parameters lose their accuracy. Moreover, variations in the cell position relative to the measurement electrodes decrease the accuracy of the analytical solutions. Impedance spectrum of a typical eukaryotic mammalian cell is generated for different geometrical configurations using finite element. The generated data are fitted to the analytical models and extracted cell parameters are compared with the original values. The results show that BH model works more effectively when chamber to cell radius ratio is <3.5 and chamber height to cell radius ratio is <3. Moreover, it is observed that analytical models estimate cell parameters with major errors when the cells are in the vicinity of the electrodes. However, for high-volume fraction simulations, the BH model was able to predict cell parameters better even in the vicinity of the electrodes.

Dielectrophoresis assisted loading and unloading of microwells for impedance spectroscopy.

Dielectric spectroscopy (DS) is a noninvasive, label-free, fast, and promising technique for measuring dielectric properties of biological cells in real time. We demonstrate a microchip that consists of electro-activated microwell arrays for positive dielectrophoresis assisted cell capture, DS measurements, and negative dielectrophoresis driven cell unloading; thus, providing a high-throughput cell analysis platform. To the best of our knowledge, this is the first microfluidic chip that combines electro-activated microwells and DS to analyze biological cells. Device performance is tested using Saccharomyces cerevisiae (yeast) cells. DEP response of yeast cells is determined by measuring their Clausius-Mossotti factor using biophysical models in parallel plate microelectrode geometry. This information is used to determine the excitation frequency to load and unload wells. Effect of yeast cells on the measured impedance spectrum was examined both experimentally and numerically. Good match between the numerical and experimental results establishes the potential use of the microchip device for extracting subcellular properties of biological cells in a rapid and nonexpensive manner.

Microfluidic Dielectric Spectroscopy of Costal Cartilage Chondrocytes

Dielectric spectroscopy allows non-invasive probing of biological cells. Information on the cell membrane, cytoplasm, and nucleus can be obtained by dielectric spectroscopy provided that appropriate experimental and numerical tools are used in specific frequency ranges. The focus of this study is to identify bioelectrical characteristics of human costal cartilage cells using a microfluidic device for dielectric spectroscopy. An in house computer program is developed to extract dielectric properties of biological cells from raw cell suspension impedance data. The algorithm utilizes Maxwell-Wagner mixture and double shell models to extract single cell dielectric spectrum and cellular dielectric parameters, respectively. The dielectric parameters of human costal chondrocytes are compared with melanoma, leukemia, and electrically excitable cardiomyoblast cells in order to comparatively assess the electrical nature of chondrocytes. The results suggest that electrical cell membrane characteristics of chondrocyte cells are closer to cardiomyoblast cells than melanoma or leukemia cells. In addition, blocking effects of Gadolinium is tested on chondrocyte, myoblast, and melanoma cells. The significant decreases in cell membrane conductance and capacitance values after treatment with Gadolinium are linked with ion channels activity on chondrocyte cell membranes.

Study on the dielectric properties of biological cells using the electrokinetic method

AbstractDifferent from hard particles with an ordinary surface structure, a biological cell is a soft particle which can be described as a hard particle covered with an ion‐penetrable surface layer of polyelectrolytes. In this paper, according to the electrokinetic theory of suspension of soft particles, the colloid vibration current (CVI) model of suspended biological cells is investigated. A CVI measurement system is set up in which ultrasonic pulses of different intensities are calibrated and used. The experimental results on electrolyte solutions and cell suspensions show that CVI is closely related to the ion and cell concentration of the sample solution. Along with the increased concentration of ions or cells, the CVI signal increased initially and then decreased for electrolyte solutions, but it was the reverse for a chicken blood cell suspension but stayed almost constant for a spawn suspension. All these phenomena were caused by the interactive electrokinetic polarization of ions and cells under the action of ultrasonic pulses. Through the analysis of the electrokinetic course of the cell suspension, it was found that the amplitude and slope of the electrokinetic curve could be used to characterize the dielectric properties of cells. The electrokinetic model and CVI measurement system are rather feasible, as shown by the experimental results. The electrokinetic measurement method shows a new nondestructive way for studying the charging properties of biological cells, and the method has an inherent advantage for the real‐time study of the biological effects of ultrasound on cells. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Dielectrophoretic capture voltage spectrum for measurement of dielectric properties and separation of cancer cells

In this paper, a new dielectrophoresis (DEP) method based on capture voltage spectrum is proposed for measuring dielectric properties of biological cells. The capture voltage spectrum can be obtained from the balance of dielectrophoretic force and Stokes drag force acting on the cell in a microfluidic device with fluid flow and strip electrodes. The method was demonstrated with the measurement of dielectric properties of human colon cancer cells (HT-29 cells). From the capture voltage spectrum, the real part of Clausius-Mossotti factor of HT-29 cells for different frequencies of applied electric field was obtained. The dielectric properties of cell interior and plasma membrane were then estimated by using single-shell dielectric model. The cell interior permittivity and conductivity were found to be insensitive to changes in the conductivity of the medium in which the cells are suspended, but the measured permittivity and conductivity of cell membrane were found to increase with the increase of medium conductivity. In addition, the measurement of capture voltage spectrum was found to be useful in providing the optimum operating conditions for separating HT-29 cells from other cells (such as red blood cells) using dielectrophoresis.

Dielectric properties of biological cells in the dipolar approximation for the single-shell ellipsoidal model: The effect of localized surface charge distributions at the membrane interface

In this paper, we describe the dielectric properties of a biological cell suspension of shelled ellipsoidal cells with a layer of localized charges at the membrane interfaces. In so doing, we are dealing with two different problems encountered in finding an analytical solution of the dielectric problem. The first one concerns the calculation of the electrical polarizability of a shelled ellipsoidal cell in the presence of a localized layer of charges. We will show that what we call the dipolar approximation is good enough to ensure a meaningful behavior of the dielectric spectra, whatever the cell parameters are, contrarily to what happens if one estimates the polarizability without taking into account the appropriate correction term deriving from the localized charge distribution. The second problem we face concerns the fact that the interfaces of the different adjacent media should be surfaces of constant coordinates, within a certain set of coordinate types. This implies, for ellipsoidal geometries, the requirement of a confocal condition which leads to a cell membrane of nonconstant thickness. Even if the membrane thickness is at least two orders of magnitude lower than the typical cell size, its nonconstancy leads to serious discrepancies in the shape of the dielectric spectra, which are heavier the larger the membrane conductivity is or larger as the value of the conductivity of the surface charge layers is. As far as this latter problem is concerned, we propose a compromise that saves the confocality condition and, at the same time, reduces significantly the effects of the nonuniform membrane thickness. We present here some dielectric spectra of shelled ellipsoidal cells (both prolate and oblate in shape) over an extended frequency range, showing their main characteristics, arising from the combined presence of localized charge distributions and polarization charge distributions. Finally, we compare some of these results with the ones obtained using different approximations.

Two-dimensional dielectric spectroscopy: Implementation and validation of a scanning open-ended coaxial probe

Dielectric spectroscopy is a powerful tool for characterizing and classifying materials based on their electrical properties. In order to perform dielectric measurements on a sample with spatially varying properties, the measuring probe typically is repositioned manually on the surface of the sample for each measurement. In this paper, we present a novel technique, based on a reconfigurable multielectrode array, which facilitates the recording of measurements at various different spatial locations without physically moving the measuring electrodes. By electronically selecting one of the electrodes as the inner line and connecting the remainder of the electrodes together to form the outer line, an open-ended coaxial probe is created, which can be repositioned by simply selecting different electrode combinations; hence the name of a "traveling" coaxial probe. The geometric factor, or the cell constant, of each coaxial probe in the array was estimated from measurements on saline solutions with known electrical characteristics. In order to validate the setup for measurement of dielectric properties of biological cells, the plasma membrane capacitance and cytoplasm conductivity of yeast cells suspended in aqueous solutions were measured and compared to results from published reports. Dielectric spectroscopy imaging was carried out on tissue phantoms made of an agar gel with inclusions consisting of concentrated yeast cell suspensions. Measurements were performed on the phantoms, and the dielectric data were spatially mapped with respect to electrode location. The spatial electrical data correlated precisely with locations of yeast cell inclusions within the phantoms.

마이크로 채널 내에서의 유전영동을 이용한 입자의 연속적인 분리에 대한 연구

In this work, a dielectrophoresis-based particle-separation device is developed which is to be used to continuously separate particles in microchannels. We fabricated the particle-separation device with combining the benefits of electrode-based DEP and insulator-based DEP. The DEP forces are generated by an array of electrodes located in both sidewalls of a main channel. According to the magnitude and frequency of electrical signals, particles with different dielectric properties experience different DEP forces, and therefore, continuously move along different streamlines in the main flow channel without need of pre-focusing process. Based on this mechanism, we examined the performance of the device by controlling the trajectory of polystyrene particles. This device is applicable to the investigation of dielectric properties of biological cells as well as the continuous separation of biological cells.

Effective Dielectric Properties of Biological Cells: Generalization of the Spectral Density Function Approach

We suggest an extension of the spectral density function approach to describe the complex dielectric response of suspensions of arbitrarily shaped particles having a thin shell, in particular, biological cells. The approach is shown to give analytical results in some simple but practically important cases. In the general case, for the 3-phase systems it reduces to determination of the spectral density function for the suspension of a certain kind. Prospects and limitations of the approach, as well as practical examples, are also considered.

Effects of membrane disruption on dielectric properties of biological cells

Disruption of the plasma membrane causes serious changes in the dielectric properties of biological cells. The changes have been simulated with spherical cell models having holes in the plasma membrane. The complex permittivity of a cubic system including a cell model was calculated by a numerical technique based on the three-dimensional finite difference method. For a cell without hole, the complex permittivity showed dielectric relaxation (β-dispersion) as predicted from interfacial polarization theories for the single-shell model. When there is one hole in the membrane, the cell has anisotropic dielectric properties depending on whether the axis through the centres of the hole and the sphere is parallel (the parallel orientation) or perpendicular (the perpendicular orientation) to the electric field direction. In the parallel orientation, dielectric relaxation (called ‘α-dispersion’) appeared at lower frequencies in addition to the β-dispersion, whereas only the β-dispersion was found in the perpendicular orientation. When there were two holes at the opposite poles of the cell, the ‘α-dispersion’ did not appear and the intensity of the β-dispersion decreased with increasing size of the holes. When two holes located in the hemisphere of the cell, however, the ‘α-dispersion’ appeared again. These results suggest that the occurrence of the ‘α-dispersion’ requires either the presence of one hole or the localization of holes.

Dielectric spectroscopy and electro-rotation of biological cells

Abstract The unusual dielectric properties of biological cells are discussed. These properties are distinguished by two main features, very high dielectric constants in excess of one thousand observed at low frequencies and three distinct relaxation processes characterized by time constants ranging from picoto milli-seconds. The mechanism responsible for these relaxation processes are summarized. The traditional technique to determine the dielectric properties of cells are frequency domain spectroscopy and, more recently, time domain spectroscopy (TDS). During the past few years the frequency dependence of the torque which cells experience in an rotating electrical field has become an additional valuable technique to determine dielectric cell properties. The fundamentals of the electro-rotation technique are stated. The comparative advantages and disadvantages of dielectric spectroscopy and electro-rotation are discussed.

Multipole interaction between dielectric particles

A method for calculating the induced multipoles on interacting dielectric spheres in the presence of an external electric field is derived. Losses in the medium and the particles are included in this model. The results for the dipole moments and the interaction force between two dielectric spheres are strongly dependent on these losses. The model can be applied to dielectric particles as well as to bubbles in a liquid, and can be useful for studying dielectric properties of biological cells.