John Mills fiddles with the knobs on a microscope, but instead of looking into the eyepiece, he stares at a sphere displayed on a laptop's screen. The laptop is connected to a video feed coming from the microscope, and Mills watches as fluids on a slide flow past the sphere, a tiny silica bead. After a few seconds, something that looks like a dented doughnut appears on the screen. It's a red blood cell, and Mills quickly adjusts the microscope's knobs until the bead "catches" the cell. He turns the knobs again, and a second silica bead appears and attaches to the cell. Then Mills slowly maneuvers the silica beads, which are coated with proteins that stick to the blood cell, so that the cell stretches out into the shape of a cigar.

Mills, a PhD student in materials science and engineering at MIT, is demonstrating what are probably the world's most powerful optical tweezers, which he built as part of his thesis work with his advisor, Subra Suresh. Optical tweezers, which were developed in the mid-1980s, use the force of light to manipulate tiny objects. In this case, Mills uses a pair of lasers to control the silica beads. Using the beads as "handles," Mills can apply a force of up to 500 pico-newtons to the red blood cell -- several times that possible with previous optical tweezers -- to test the elasticity of the cell's wall.