Manipulation of single fine particle in liquid by electrical force in combination with optical pressure

The use of optoelectrostatic micromanipulation, i.e. electric force in combination with the optical pressure of a focused laser beam, for manipulating biological cells was studied experimentally. The optical pressure has two components, the optical confinement pressure and the optical drift pressure. Cells are confined in the focused laser beam by the former, and the confined cells are pushed downstream of the laser by the latter. The optical drift velocity of yeast cells dispersed in water was measured using an Ar laser and amounted to 460 mu m/s at a laser power of 500 mW. The light pressure and the electrical force were combined by using an electrode system with an insulating slit to form the DC electric field. The yeast cell acquired negative charge in deionized water and then, confined in the laser beam, was manipulated on the axis of the laser beam. As an example of the technique, a cell feeder by which a single cell can be fed successively on the beam axis was constructed. A process for extracting yeast cells from water to air utilizing optical pressure and electrical force was also tested. A cell was optically transported to the surface, where a DC electric field was used to transfer the cells to gas or vacuum where high-speed sorting or analysis can be performed. The techniques described can also be applied to molecules.<>