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Controlling the Flow

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Consumers around the world delight in printing high-resolution photos on inkjet printers in their own homes. Scientists are excited by DNA sequencers so small and efficient they fit on a single chip. And even the least science-minded among us cannot help but be thrilled by the prospect of directly manipulating a single molecule of DNA. These are all examples of microfluidics at work. Breakthroughs in this new field of nanotechnology are largely thanks to the sets of very, very tiny tools being developed by applied physicist Professor Stephen Quake.

On the cutting edge of biotechnology, physics, chemistry and engineering, Quake is a pioneer in the promising young field of microfluidics, which works with sub-millilitre quantities of fluids manipulated on chips. He and his team manipulate drops of liquid so small they're invisible to the naked eye.

One of Quake's most important inventions was the integrated fluidic circuit (IFC). IFCs are microscale devices with mechanical parts that allow researchers to run experiments with quantities of liquids at the nano level - volumes thousands of times smaller than the finest of mists.

The challenge was to come up with a device that could be used for a broad range of applications, incorporating multiple functions on a single chip. They solved this problem by creating a set of microfabricated valves and pumps cast out of soft, elastomeric silicone rubber in reusable moulds. The elastomer is cheaper to work with and allowed researchers to reduce the size of IFCs by more than two orders of magnitude compared to the other microfluidic devices available at the time. The postage stamp-sized chip is less than one-half the width of a human hair. An added benefit: the optically clear elastomer means reactions can be observed directly, even as they are occurring.

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Snapshot (JPG)

How it works

The integrated fluidic circuit (IFC) system consists of a membrane that deflects under pressure to pinch off the flow of fluids in a microchannel. The valve is made from two separate layers of optically clear elastomeric rubber that have been placed on a micro-machined mould so that grooved recesses are formed on one side of each layer. By bonding the layers together, the recesses form channels that crisscross in a solid structure.

The structure is sealed onto the top of a glass surface; together with the recesses of the bottom layer, they form the liquid "flow" channel. When pressurised gas is applied to the channels of the upper layer, the rubber deflects at precisely the intersection of the channels in the bottom layer - a simple, yet effective valve.

Fluid is introduced into the IFC flow channels through steel pins inserted into the silicone. These inlets accept pressures of up to 300 kPa without leakage. The IFC can be designed to actuate some valves but not others by varying the width of the elastomer and adjusting actuation pressures.

At a glance

Inventors:
Stephen R. Quake (US), Marc A. Unger (US), Hou-Pu Chu (US), Todd A. Thorsen (US), Axel Scherer (US)
Invention:
Microfabricated elastomeric valve and pump systems
Company:
California Institute of Technology

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