Electrical properties of breast cancer cells from impedance measurement of cell suspensions

Impedance spectroscopy of biological cells has been used to monitor cell status, e.g. cell proliferation, viability, etc. It is also a fundamental method for the study of the electrical properties of cells which has been utilised for cell identification in investigations of cell behaviour in the presence of an applied electric field, e.g. electroporation. There are two standard methods for impedance measurement on cells. The use of microelectrodes for single cell impedance measurement is one method to realise the measurement, but the variations between individual cells introduce significant measurement errors. Another method to measure electrical properties is by the measurement of cell suspensions, i.e. a group of cells within a culture medium or buffer. This paper presents an investigation of the impedance of normal and cancerous breast cells in suspension using the Maxwell-Wagner mixture theory to analyse the results and extract the electrical parameters of a single cell. The results show that normal and different stages of cancer breast cells can be distinguished by the conductivity presented by each cell. © 2010 IOP Publishing Ltd

The prolate-to-oblate shape transition of phospholipid vesicles in response to frequency variation of an AC electric field can be explained by the dielectric anisotropy of a phospholipid bilayer

The external electric field deforms flaccid phospholipid vesicles into spheroidal bodies, with the rotational axis aligned with its direction. Deformation is frequency dependent: in the low frequency range (~ 1 kHz), the deformation is typically prolate, while increasing the frequency to the 10 kHz range changes the deformation to oblate. We attempt to explain this behaviour with a theoretical model, based on the minimization of the total free energy of the vesicle. The energy terms taken into account include the membrane bending energy and the energy of the electric field. The latter is calculated from the electric field via the Maxwell stress tensor, where the membrane is modelled as anisotropic lossy dielectric. Vesicle deformation in response to varying frequency is calculated numerically. Using a series expansion, we also derive a simplified expression for the deformation, which retains the frequency dependence of the exact expression and may provide a better substitute for the series expansion used by Winterhalter and Helfrich, which was found to be valid only in the limit of low frequencies. The model with the anisotropic membrane permittivity imposes two constraints on the values of material constants: tangential component of dielectric permittivity tensor of the phospholipid membrane must exceed its radial component by approximately a factor of 3; and the membrane conductivity has to be relatively high, approximately one tenth of the conductivity of the external aqueous medium.Comment: 17 pages, 6 figures; accepted for publication in J. Phys.: Condens. Matte

Electrode Polarization Effects in Broadband Dielectric Spectroscopy

In the present work, we provide broadband dielectric spectra showing strong electrode polarization effects for various materials, belonging to very different material classes. This includes both ionic and electronic conductors as, e.g., salt solutions, ionic liquids, human blood, and colossal-dielectric-constant materials. These data are intended to provide a broad data base enabling a critical test of the validity of phenomenological and microscopic models for electrode polarization. In the present work, the results are analyzed using a simple phenomenological equivalent-circuit description, involving a distributed parallel RC circuit element for the modeling of the weakly conducting regions close to the electrodes. Excellent fits of the experimental data are achieved in this way, demonstrating the universal applicability of this approach. In the investigated ionically conducting materials, we find the universal appearance of a second dispersion region due to electrode polarization, which is only revealed if measuring down to sufficiently low frequencies. This indicates the presence of a second charge-transport process in ionic conductors with blocking electrodes.Comment: 9 pages, 6 figures, experimental data are provided in electronic form (see "Data Conservancy"

Correlated errors in Hipparcos parallaxes towards the Pleiades and the Hyades

We show that the errors in the Hipparcos parallaxes towards the Pleiades and the Hyades open clusters are spatially correlated over angular scales of 2 to 3 deg, with an amplitude of up to 2 mas. This correlation is stronger than expected based on the analysis of the Hipparcos catalog. We predict the parallaxes of individual cluster members, pi_pm, from their Hipparcos proper motions, assuming that all cluster members have the same space velocity. We compare pi_pm with their Hipparcos parallaxes, pi_Hip, and find that there are significant spatial correlations in pi_Hip. We derive a distance modulus to the Pleiades of 5.58 +- 0.18 mag using the radial-velocity gradient method. This value, agrees very well with the distance modulus of 5.60 +- 0.04 mag determined using the main-sequence fitting technique, compared with the value of 5.33 +- 0.06 inferred from the average of the Hipparcos parallaxes of the Pleiades members. We show that the difference between the main-sequence fitting distance and the Hipparcos parallax distance can arise from spatially correlated errors in the Hipparcos parallaxes of individual Pleiades members. Although the Hipparcos parallax errors towards the Hyades are spatially correlated in a manner similar to those of the Pleiades, the center of the Hyades is located on a node of this spatial structure. Therefore, the parallax errors cancel out when the average distance is estimated, leading to a mean Hyades distance modulus that agrees with the pre-Hipparcos value. We speculate that these spatial correlations are also responsible for the discrepant distances that are inferred using the mean Hipparcos parallaxes to some open clusters. Finally, we note that our conclusions are based on a purely geometric method and do not rely on any models of stellar isochrones.Comment: 33 pages including 10 Figures, revised version accepted for publication in Ap

The dielectric response of spherical live cells in suspension: An analytic solution

We develop a theoretical framework to describe the dielectric response of live cells in suspensions when placed in low external electric fields. The treatment takes into account the presence of the cell's membrane and of the charge movement at the membrane's surfaces. For spherical cells suspended in aqueous solutions, we give an analytic solution for the dielectric function, which is shown to account for the alpha and beta plateaus seen in many experimental data. The effect of different physical parameters on the dielectric curves is methodically analyzed.Comment: 8 pages, 9 figure