Number 47 (Story #1), September 13, 1991 by Phillip F. Schewe and Ben Stein DNA MOLECULES CAN BE MANIPULATED with "optical tweezers." Steven Chu of Stanford, a pioneer in the cooling and trapping of neutral atoms, has been able to grasp individual biological molecules by attaching to them polystyrene spheres. This allows Chu, for example, to study the mechanical properties of a DNA molecule by stretching apart its ends using two independently focussed laser beams. In its stretched state, the molecule can be "spot welded" to a microscope slide, where it can be glimpsed by scanning probe microscopes. (Science, 23 August 1991.)