Transport of microscopic objects using asymmetric transverse optical gradient force

We report an efficient technique based on an optical tweezers setup for optically controlled transport of microscopic objects. The technique makes use of an elliptically profiled trap beam that has an asymmetric intensity distribution about the center of its long axis. Microscopic objects pulled into the trap from the side having the larger intensity gradient become accelerated along the major axis of the focus and are ejected from the lower-stiffness end. The speed of transport is determined by the laser-beam power and the degree of asymmetry in the intensity profile. The approach could be used to simultaneously trap and transport hundreds of particles, varying in sizes from sub-micrometer to a few micrometers. Further, transport of red blood cells using this method is demonstrated.