Henning Glasser

Cell manipulation and cultivation under a.c. electric field influence in highly conductive culture media

Extreme miniaturisation of electrodes enabled us to apply high-frequency electric fields (between 100 kHz and several hundred MHz) of field strengths up to 50 kV/m into cell suspensions of high conductivity (several S/m), such as original cell culture media. The active electrode areas were additionally decreased and modified by insulating the terminals and/or coating of the electrodes with thin dielectric layers. Micro scaled electrode structures were fabricated on glass or silicon wafers in semiconductor technology. It could theoretically and experimentally be shown that cells exhibit exclusively negative dielectrophoresis if suspended in highly conductive media. Therefore, they can be repulsed from surfaces by appropriate arrangements of electrodes and easily be manipulated in free solution. Adherently growing animal cells, like mouse fibroblasts (3T3, L929), were cultivated in Dulbeccos Modification of Eagles Medium (DMEM) or RPMI 1640 under permanent field application (frequency: 10 MHz, field strength: 50-100 kV/m).

Particle micromanipulator consisting of two orthogonal channels with travelling-wave electrode structures.

Abstract In the paper experimental and numerical results for a simple particle micromanipulator fabricated in silicon technology are presented. It consists of three orthogonal liquid filled channels above meander-shaped planar electrode strips. By applying appropriate alternating, rotating or travelling electric fields in the chamber dielectric forces acting on particles suspended in the liquid are induced allowing trapping, movement and separation of them. The efficient manipulation of small particles with typical dimensions of several micrometers using electrogradient techniques (EGT) requires electrode structures of the same size. Due to the complex electrode geometry a numerical procedure is used for calculation of particle trajectories and optimising the design. In the micro range small fabrication defects are likely to cause large changes of the properties of the manipulator. Therefore, a test procedure based on electrode processes in aqueous media and the pH-dependent fluorescence intensity of a marker solution which enabled us to visualise the working states, surface coatings and fabrication defects of microstructured electrodes via a microscope is introduced.