MANIPULATION OF SINGLE FINE PARTICLE IN LIQUID BY ELECTRICAL FORCE IN COMBINATION WITH OPTICAL PRESSURE

In order to manipulate biological cells or molecules, the opt-electrostatic micromanipulation has been proposed utilizing electrical force in combination with optical pressure of a focused laser beam. The optical pressure has two components: the optical confinement pressure and the optical drift pressure. Due to the optical confinement pressure, cells can be confined in the focused laser beam. The confined cells are pushed away towards the downstream of the laser by the optical drift pressure. The optical drift velocity of yeast cells dispersed in water was measured using an argon-ion laser and was 460-mu-m/s at a laser power of 500 mW. The combination of light pressure and electrical force was made using an electrode system having an insulating slit. The laser was focused at the center of the slit, where a dc electric field was formed. The yeast cell acquired negative charge in deionized water. The cell, confined in the laser beam, could be manipulated on the axis of the laser beam by adjusting the dc voltage and the laser power. As an example, a cell feeder was constructed, by which single cells can be fed successively on the beam axis. An extraction process of yeast cells in water to air was also tested by utilizing the optical pressure and the electrical force. A cell was optically transported to the surface, where a dc electric field was formed to extract the cell. This process may be used to supply biological cells or molecules in gas or vacuum, where high-speed sorting or analysis can be made.