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.
[Click here for images of Suresh and his team at work.]
Using such ultrasensitive tools to measure the physical properties of a cell, such as its stiffness, “will let us look at things in ways we haven’t done before,” says Suresh, a professor in MIT’s Department of Materials Science and Engineering. For example, Suresh and his team are examining the way a force applied by the tweezers affects a healthy red blood cell, and then comparing the way a cell infected with a malaria parasite responds to a similar force. Suresh hopes that knowing precisely how malaria changes the physical properties of a cell could lead to better ways to treat the disease, or even to prevent it.
Studying such properties of biological components is relatively new ground for Suresh. As a materials scientist, he has spent much of his career studying the structural properties of materials used, say, as coatings or in thin films. While in France on sabbatical in April 2004, he spoke at a prestigious technical school in Paris, where he had a chance encounter at the cafeteria with a biology professor. The biologist did research at the Institut Pasteur and invited Suresh to speak there about his work.
The reaction of the biologists was enthusiastic. They weren’t using the precise tools – such as optical tweezers – that are relatively common in Suresh’s field. And they saw that Suresh’s expertise, experiments, and computer modeling might help them understand some of the physical changes that diseased cells undergo.