Hot-and-cold chips with running fluids

时间:2019-03-07 06:04:05166网络整理admin

By Jonathan Knight TINY rivers may help solve the problem of how to move liquids around in biochips—devices that combine electronic and biological functions on a silicon wafer. Engineers at Princeton University say they can channel liquids over the chip by setting up small temperature gradients. The challenge of handling minuscule volumes of liquid has hampered the development of labs-on-a-chip. On this scale, water is more like treacle, gumming up pumps, valves and mixers. Molecules on the surface of a liquid will flow towards regions of higher surface tension. Because surface tension increases as temperature drops, Sandra Troian and Dawn Kataoka realised that they could use this principle to channel liquids. They placed a silicon chip across two brass blocks, one 4 °C cooler than the other, and added oil to the warm side of the chip. Shallow channels in its surface, each narrower than a human hair, guided the flow allowing rivers of oil only 1 micrometre deep to flow across the chip. “Essentially, the cold part is pulling on the warm part,” says Troian. Microscale heaters to control the temperature within a chip already exist and could be programmed to heat and cool the surface in any pattern. For reagents to mix, Troian says, the streams merely need to intersect. “It’s a neat way to move liquids around,” says Dorian Liepmann, a microfluidics expert at the University of California,