Combined detection of AC-electrokinetic effects: Experiments with three-axial chicken red blood cells.

Abstract

Dielectrophoresis (DEP), electrorotation (ROT), and electro-orientation were used for the dielectric spectroscopy of nucleated three-axial chicken red blood cells (CRBCs). Because the different AC-electrokinetic effects are not mutually independent, their DEP and ROT spectra were combined in ranges separated by the reorientation of the CRBCs in the inhomogeneous linear DEP and circular ROT fields. This behavior can be qualitatively described by a single-shell ellipsoidal model. Whereas in linear fields, the maximum of the Clausius-Mossotti factor along the three axes determines the orientated axis, in circular fields, the minimum of the factor determines the axis perpendicularly orientated to the field plane. Quantitatively, it has not been possible to find a consistent parameter set for fitting the DEP and ROT spectra, as well as the reorientation frequencies. Our ellipsoidal CRBC standard model had semiaxes of a=7.7μm, b=4.0μm, and c=1.85μm, a relative permittivity of 35 to 45 and conductivity of 0.36 to 0.04S/m for the cytoplasm, combined with a specific capacitance of 10 to 14mF/m2 and a conductivity of 3500S/m2 for the cell membrane. The fits in different external conductivity ranges between external conductivities of 0.015 and 1.0S/m were improved when the membrane capacitance was changed between 4 to 25mF/m2 depending on the method used. A similar transition was reflected in the effective properties of a three-shell spherical model containing an internal membranous sphere with the geometry of the CRBC nucleus. Our findings suggest that the simultaneous interpretation of various AC-electrokinetic spectra is a step toward the dielectric fingerprinting of biological cells.