PopSci's 2nd Annual Brilliant 10

STEPHEN QUAKE


Microfluidics: CalTech


Building a computer from a plumber's nightmare of miniature pipes.




Stephen Quake twirls between his fingers a transparent, rubbery square the size of a postage stamp. "You can make them out just barely," he says, his eyes on its minuscule labyrinth of canals, each of which contains millionths of a raindrop's worth of fluid. Quake is holding a miniature chemistry lab, in which pint-size beakers are replaced by channels the width of a human hair. A typical chip hosts a plumber's nightmare of 1,000 chambers linked by some 3,500 valves. Here, by mixing tiny doses of chemicals in countless combinations, researchers can speedily puzzle out the blueprint of a human gene, or test thousands of variations of potential drug compounds to rapidly seek cures for diseases.




Quake, 34, is helping forge a new discipline: microfluidics. His chips have more than biological applications; they also work as computers. The
basic element of a computer is a bit—a 1 or 0 that stays as it is until the machine tells it to change. Writing in Science in May, Quake and colleagues unveiled a bit made of liquids. The bit is stored in a cell consisting of channels that meet at a four-way intersection. Clear fluid flows from the left, and blue fluid comes in from the right. The blue fluid contains polymers that stretch when the fluid passes through a nozzle at the intersection; the stretched polymers hang together, and as a result, the blue and clear fluids don't mix. Instead, at the intersection the blue fluid goes one way—say, up—and the clear goes down. The scenario won't change until something acts upon the fluids, so it represents a bit—say, a 1. To change that bit to a 0, Quake applies a pressure pulse. That disturbance forces the blue fluid down, switching the bit to a 0. Though Quake won't be factoring large primes anytime soon, he has demonstrated that microscopic fluidic circuits are possible.




When Quake began, microfluidic chips were etched with difficulty into hard

silicon. He experimented with silicone and found it more suitable. His new chips possess thousands more channels than their silicon forebears, and 300 to 500 times more valves than his competitors' chips. And they keep getting smaller. "One thing led to another," he says, "and before you know it, we'd invented really powerful tools."




—Charles Q. Choi