Measurement of dielectrophoretic force by employing controllable gravitational force

Dielectrophoresis (DEP) is the motion of a matter caused by polarization effects in a non-uniform electric field. Recently, studies on DEP are promoted in various medical fields, including separation and characterization of biological cells. It is very important but not easy to measure this motive force, so-called dielectrophoretic force (DEP force). In general, the DEP force generated by the designed electrodes is analyzed by the computer simulation that employs the finite element analysis method. However, it does not always calculate the correct DEP force. Therefore, we propose the method of measuring the DEP force accurately based on the null method. The experiment is conducted with the dielectrophoretic device (DEP device) in which microfabricated electrodes were formed and which contains the polystyrene particles exhibiting the negative DEP in distilled water in a non-uniform electric field. The displacement of the particle reaches a steady state 15 min. after the change of applied voltage v, angle θ or frequency f. The equilibrium state of the particle in a non-uniform electric field can be reached at any place by adjusting both of angles θ and φ, where θ is the “Pitch” angle and φ the “Yaw” angle for the device. The proposed method can measure the incredibly minute DEP force ranging from 25 fN (femto-Newton) at θ=5° to 298 fN at θ=90°, the accuracy of which is determined by the static friction and rolling friction between particles and the inner floor of the DEP device.