Measurements of dielectrophoretic collection spectra of Escherichia coli and Staphylococcus aureus suspensions are used for obtaining dielectric characteristics of both types of bacteria. The experiments are interpreted using a numerical method that models the cells as compartmented spherical or rod-like particles. We show the usefulness of this simple method to extract significant information about the electrical properties of Gram-negative and -positive bacteria.

Progress in microelectrode-based technologies has facilitated the development of sophisticated methods for manipulating and separating cells, bacteria, and other bioparticles. For many of these various applications, the theoretical modeling of the electrical response of compartmentalized particles to an external field is important. In this paper we address the analysis of the interaction between cells immersed in rf fields. We use an integral formulation of the problem derived from a consideration of the charge densities induced at the interfaces of the particle compartments. The numerical solution by a boundary element technique allows characterization of their dielectric properties. Experimental validation of this theoretical model is obtained by investigating two effects: (1) The influence that dipolar "pearl chaining" has on the dielectrophoretic behavior of human T lymphocytes and (2) the frequency variation of the spin and orbital torques of approaching insulinoma beta-cells in a rotating field.

The problem of structure formation in colloidal systems composed of polarizable and conducting particles is considered. It is demonstrated that, in certain frequency ranges of the applied field, the dipole interaction leads to patterns whereby particles of different types are connected across field lines. By applying a Monte Carlo simulation, the main characteristics of the chaining process in a mixture of polystyrene beads and yeast cells are analysed. A good correlation between the theoretical model applied and experimental data is achieved. The data show that different aggregation patterns occur as a function of frequency.

Using an electrostatic model for the pore and membrane region in a gramicidinlike channel, the effect of dipoles located inside the membrane on the ion transport are analyzed. Calculated energy profiles for different orientations of dipoles show a predominant influence of their radial components. The results qualitatively agree with experimental measurements of conductance on different modified gramicidins and allow to understand the important role of polar side chains on ion permeation.

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When an intense radio-frequency field is applied to a suspension of dielectric particles, the suspended phase condenses under the effect of dipolar interactions between particles. We study the interaction energy when losses are present and address the problem of the formation of linear structures, using a Monte Carlo simulation. We find features of a cooperative phenomenon, with a threshold of field intensity. The dependence of the process with concentration, field intensity, and frequency is studied.

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We predict the complex polarizability of a realistic model of a red blood cell (RBC), with an inhomogeneous dispersive and anisotropic membrane. In this model, the frequency-dependent complex electrical parameters of the individual cell layers are described by the Debye equation while the dielectric anisotropy of the cell membrane is taken into account by the different permittivities along directions normal and tangential to the membrane surface. The realistic shape of the RBC is described in terms of the Jacobi elliptic functions. To calculate the polarizability, we evoke the effective dipole moment method to determine the cell internal electric field distribution, employing an adaptive finite-element numerical approach. We have furthermore investigated the influence of the anisotropic membrane and dispersive electrical parameters of each individual cell layer on the total complex polarizability. Our findings suggest that the individual layer contribution depends on two factors: the volume of the layer and the associated induced electric field, which in turn is influenced by other layers of the cell. These results further show that the average polarizability spectra of the cell are significantly impacted by the anisotropy and associated dispersion of the cellular compartments.