The considerable amount of activity in the field of electrofusion and electropermeabilization is very promising from the point of view of new insights into biomembranes and new technologies in the future for the production of new compounds and modification of cell systems for nutrition, energy production and the removal of waste products. It is particularly gratifying to see how basic science has provided the foundation for a useful technology, although in some cases the time needed to develop an application is very long. In other cases, it is necessary to overcome the difficulties posed by existing schools of thought which have been shown to be wrong. It is fascinating to observe the many developments and discoveries in the areas of physics, material science, space technology and electronics which are just waiting to be applied to biological systems. An increased interdisciplinary collaboration between physicists and biologists could provide considerable impetus to biology and its application in technology. However, this can only be achieved if basic research into biological membranes is accelerated. The techniques for electrical breakdown, electropermeabilization and electrofusion could be an important tool in this process, since we cannot rule out the possibility that the high electrical fields occurring naturally in the membrane play an important role in the selective transport of substances across the membrane as well as in natural regulatory processes.

Electrical breakdown, electropermeabilization and electrofusion

Holding forces of single-particle dielectrophoretic traps.

The traveling-wave-induced linear transfer of dielectric particles like living cells and artificial objects of microscopic dimensions is analyzed. It is shown that the electrode geometries must correspond to particle sizes to allow an effective manipulation of particles immersed in weakly electrolytic solutions by high frequency traveling waves. The theoretical model elaborated in this paper is in good agreement with experimental results obtained in microfabricated chambers of linearly arranged electrodes. It explains the behavior of homogeneous cellulose spheres as well as that of membrane-covered pine polls. The traveling-wave-driven electrodes are described by a superposition of time-dependent point charges. Subsequently, each of these point charges has to be considered as polarizing the dielectric particle and interacting with the polarized particle. This results in forces which effectively translocate the particle.

Traveling-wave dielectrophoresis of microparticles.

Levitation, holding, and rotation of cells within traps made by high-frequency fields.

Dielectrophoretic levitation of spheres and shells

A dielectrophoretic levitation scheme is used to measure the dielectric constant of insulating dieletric liquids and small solid spherical particles. The fixed ring-disk electrode system is first calibrated against a known standard dielectric liquid by levitating a small gas bubble in the liquid at a fixed location. The measurements are then performed by measuring the voltage required to levitate a gas bubble in the unknown liquid at the same location with respect to the electrode structure. A similar procedure is used for solid spherical particles. The system is unique because it requires no detailed knowledge of the electric field. Fabrication of the electrodes does not require precision machining, and the structure is relatively insensitive to leveling. The size of the gas bubble or solid particle is not critical as long as it is much smaller than the electrode structure. The measurement precision is limited by the accuracy of the voltage measurements and by the accuracy to which the dielectric constant (of the standard) and the specific gravities (of the unknown and the standard) are known. The measurements presented support the contention that this method is a simple and reliable method of measuring the dielectric constant of insulating dielectric liquids.

Gregory A. Kallio

Papers

Dielectric Constant Measurements Using Dielectrophoretic Levitation