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Mini DNA replicator could benefit world's poor 16:08 01 May 2007 NewScientist.com news service Mason Inman
A pocket-sized device that runs on two AA batteries and copies DNA as accurately as expensive lab equipment has been developed by researchers in the US. The device has no moving parts and costs just $10 to make. It runs polymerase chain reactions (PCRs), to generate billions of identical copies of a DNA strand, in as little as 20 minutes. This is much faster than the machines currently in use, which take several hours. "I hope this will make PCR more available," says Victor Ugaz of Texas A&M University in Texas, US, whose group made the new device. He says the system could enable DNA-based tests to be carried out in the field or in developing countries, where large, expensive laboratory equipment is neither practical nor affordable. Running a PCR requires treating DNA strands, along with chemical materials needed to make new DNA strands, at three different temperatures. The highest temperature (95°C) causes two strands of a DNA molecule to separate. The lowest temperature (60°C) makes DNA building blocks stick together. Then, holding the temperature in the middle (72°C), allows an enzyme to quickly assemble replica DNA strands. To cycle through these temperatures, a conventional PCR machine heats and cools a large metal block holding multiple tubes containing samples of DNA and the material needed to make copies. In the new device, created by graduate student Nitin Agrawal, a centimetre-wide loop of tubing wraps in a vertical ring around a set of three metal rods. The rods, together the size of an AA battery, are kept at three different temperatures. With this set-up, the parts of the tube closest to each block are heated differently. This keeps the liquid flowing through the millimetre-wide tube, and so the DNA and building blocks cycle automatically through the three temperatures needed for PCR. "It's similar to how a lava lamp works," says Ugaz. As the fluid is heated, it becomes less dense and more buoyant, so it flows upward. When the fluid cools in another part of the loop, it becomes denser and moves down. And because the device only heats the three small blocks of metal, it also runs off just two AA batteries. "This is a significant advance in the proof of the concept," says biomedical engineer Samuel Sia of Columbia University in New York, US. "It shows you can use convection-driven flow to do PCR in a miniaturized format."The device shows promise for a variety of tests, Sia says, including monitoring levels of HIV virus in a person's body or diagnosing tuberculosis. "There's nothing like this in developing countries," he explains. "There's a great need everywhere in the world for doing DNA- and RNA-based tests."For the full potential of the device to be realised, however, Sia says that cheap and simple methods of preparing samples, by isolating DNA from cells, will be needed along with miniaturised DNA analysis equipment. Journal reference: //Angewandte Chemie International Edition// (DOI: 10.1002/anie.200700306)
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