AC-Electrokinetic Applications in Cell Chips: Basic Understanding and Modeling of Structural Polarization Effects

Abstract

AC fields induce charges at the structural interfaces of particles and biological cells. The interaction of these charges with the inducing field generates forces which are the basis for AC-electrokinetic effects such as electrorotation (ER), dielectrophoresis (DP), electroorientation, electrodeformation, field-trapping and travelling wave dielectrophoresis (TWDP). The effects can be used for the dielectric characterization or manipulation of single objects. While the observed effect depends on the field quality, the frequency dependence of the dipole moment induced in the object generates particular frequency spectra. Because the effects are not independent one of each another, combined force spectra can be observed, e.g. broken DP and ER spectra with ranges separated by the reorientation of non-spherical objects in inhomogeneous linear and rotating fields, respectively. A simple mechanistic description of structural object polarizations is given together with qualitative explanations for the various AC-electrokinetic effects. The influential-radius notion allows for the separation of the geometric and electric problems of object polarization. The separate consideration of the electric model in certain frequency bands allows for easy simplifications of the model.