Electrophoretic levitation and focusing of particles by field switching.

An electric field parallel to electrode arrays, which can be realized by switching DC electric fields, allows the electrophoretic levitation and focusing of negatively charged particles at the height of the anodes in the electrode arrays. Electric field calculations predict that charged particles will migrate parallel to the electrode array. The trajectories of particles well reflect the calculated electrical field. The present principle is also applied to the focusing and sweeping of the particles. Results obtained with varying experimental variables indicate that an increase in applied voltage results in a linear increase in an initial focusing rate but lowers the focusing efficiency. Also, the focusing efficiency is enhanced with decreasing intervals of field-switching. These results strongly suggest that the elimination of the large lateral movements of particles is important to attain high focusing efficiency.