A UNIFIED RESISTOR-CAPACITOR MODEL FOR IMPEDANCE, DIELECTROPHORESIS, ELECTROROTATION, AND INDUCED TRANSMEMBRANE POTENTIAL

Dielectric properties of suspended cells are explored by analysis of t he frequency-dependent response to electric fields. Impedance (IMP) re gisters the electric response, and kinetic phenomena like orientation, translation, deformation, or rotation can also be analyzed. All respo nses can generally be described by a unified theory. This is demonstra ted by an RC model for the structural polarizations of biological cell s, allowing intuitive comparison of the IMP, dielectrophoresis (DP), a nd electrorotation (ER) methods. For derivations, cells of prismatic g eometry embedded in elementary cubes formed by the external solution w ere assumed. All geometrical constituents of the model were described by parallel circuits of a capacitor and a resistor. The IMP of the sus pension is given by a meshwork of elementary cubes. Each elementary cu be was modeled by two branches describing the current flow through and around the cell. To model DP and ER, the external branch was subdivid ed to obtain a reference potential. Real and imaginary parts of the po tential difference of the cell surface and the reference reflect the f requency behavior of DP and ER, The scheme resembles an unbalanced Whe atstone bridge, in which IMP measures the current-voltage behavior of the feed signal and DP and ER are the measuring signal. Model predicti ons were consistent with IMP, DP, and ER experiments on human red cell s, as well as with the frequency dependence of field-induced hemolysis , The influential radius concept is proposed, which allows easy deriva tion of simplified equations for the characteristic properties of a sp herical single-shell model on the basis of the RC model.