Single-beam optical trapping and micromanipulation of mammalian cells

Abstract

A single-beam gradient force optical trap was combined with a pulsed UV laser microbeam In order to perform laser Induced cell fusion. This combination offers the possibility to selectively fuse two single cells without critical chemical or electrical treatment. The optical trap was created by directing a Nd:YAG laser, at a wavelength of 1.06 jim, into a microscope and focusing the laser beam with a high numerical aperture objective. The UV laser microbeam, produced by a nitrogenpumped dye laser (366 rim), was collinear with the trapping beam. The maximum transverse force exerted on a moving cell (NS- 1) by the optical trap was determined by measuring the velocity at which the cell fell out of the trap. For a laser power of 55 mW and a cell diameter from 9 to 20 rim, the drag force was calculated using Stokes' law to be in the range from 1.42 0.22 x 106 to 1.13 0.25 x 10-6 dynes. For the fusions, the transverse force needed to capture two NS- 1 cells and to bring them into close contact, was > 200 mW. Once inside the trap, two cells could be fused with several pulses of the UV laser microbeam, attenuated to an energy of 1 &J/pulse In the object plane. This method of laser Induced cell fusion should provide Increased selectivity and efficiency in generating viable hybrid cells.