Researchers from the University of Chicago presented their findings on the use of light to continuously sort microscopic particles at the March meeting of the American Physical Society in Austin, Texas. The technique, which they call optical fractionation, is based on team leader David G. Grier's earlier work in the development of holographic optical tweezers.The tweezers incorporate computer-generated holograms into the laser setup to produce arrays of optical traps in arbitrary and dynamic three-dimensional patterns. Optical fractionation uses the optical potential landscapes created with the technique to sort materials by size, shape, dielectric constant and surface charge density.