Forces on biological cells due to applied alternating (AC) electric fields. I. Dielectrophoresis.

Measurements are presented of dielectrophoretic forces for SP2 (mouse) and K562 (human) cells in external alternating electric fields over a frequency range of 10 kHz to 2 MHz. Using a spherical shell model of the cell, the dielectrophoretic force is derived from the interaction between the induced electric dipole moment in the cell and the external electric field. The frequency dependence of the force has its origin in the dispersion with frequency of the impedances of the cell membrane, the cytoplasm and the external medium (a Maxwell-Wagner dispersion). The predicted tri-phasic form of the variation of the dielectrophoretic force is in good agreement with the experimental results presented. Using the theoretical model, the experimental measurements also provided an estimation of 0.18 +/- 0.03 S m-1 and 0.12 +/- 0.04 S m-1 for the conductivities of the cytoplasm of cells of SP2 and K562, respectively, and 6.0 +/- 2.0 mF m-2 and 2.0 +/- 1.0 mF m-2 for the capacitances of the plasma membrane of these cells.