A comprehensive approach to electro-orientation, electrodeformation, dielectrophoresis, and electrorotation of ellipsoidal particles and biological cells

Suspended cells may respond to AC polarization by orienting, deforming, moving or rotating. For modeling of ellipsoidal cells, a new dipole approach is proposed. Along each of the principal axis of the model, three finite elements of arbitrary but equal cross-sectional area for the interior, low conductive membrane shell and exterior are assumed. The length of the external medium elements is defined by influential radii which are related to the depolarizing factors. The model predicts the potential at the ellipsoid's surface leading to the induced dipole moment. The moment obtained is identical to the Laplace approach for homogeneous ellipsoids; in the single-shell case, it is slightly different. The reason is the constant shell thickness which overcomes the confocal thickness necessary for the Laplace solution. Expressions for electro-orientation, deformation, dielectrophoresis, and electrorotation are derived. In linearly and circularly polarized fields, different orientation spectra are predicted to occur. While in linearly polarized AC fields, particles are oriented along their axis of highest polarizability, in circularly polarized fields, the axis of lowest polarizability is oriented perpendicular to the plane of field rotation. Based on this finding, a new electro-orientation method is proposed. In dielectrophoresis and electrorotation, reorientations are predicted which lead to discontinuous spectra. (C) 2001 Elsevier Science B.V. All rights reserved.