Laser tweezers control micro-organism collisions for virus-cell research

March 1, 1997

Investigators from the National Institute of Standards and Technology (Gaithersburg, MD) and Harvard University (Cambridge, MA) are using dual optical tweezers to merge virus-coated microspheres and red blood cells. Each tweezer traps particles and micro-organisms at the focal point of the beam after it passes through an objective lens. The change in momentum of the light transmitted by the particle exerts a restorative force, trapping it. The traps are set using a linearly polarized, 2-W Nd:YAG laser beam that is expanded, collimated, and split into two orthogonally polarized beams; power is 20 mW in each. In a phosphate-buffered saline solution, one beam holds the red blood cell while the other moves the microsphere to it.

These optically controlled collisions (OPTCOLs) can determine the probability of adhesion on collision in the presence and absence of a sialic-acid-bearing inhibitor. The effectiveness of such inhibitors cannot be determined by other means. The OPTCOL technique showed, for example, that the most potent inhibitor of influenza prevented attachment 50% of the time. The technique also can determine the influence of relative orientation and velocity of the biological objects.