A pocket-sized $10 device that can 鈥渁mplify鈥� DNA is promising a cheap, portable method for diagnosing HIV and TB. Like existing lab equipment, the device uses the polymerase chain reaction (PCR) to amplify a sample, but is does this in as little as 20 minutes, rather than the hour or two usually needed. 鈥淚 hope this will make PCR more available,鈥� says Victor Ugaz of Texas A&M University in College Station, whose group developed the device.
To amplify a small sample of DNA it is first heated to a series of different temperatures to make its double strands uncoil and separate into single strands. These are then bound to the polymerase enzyme, which copies them, greatly increasing the quantity of DNA in the sample. In traditional PCR machines, tubes containing the sample are held in a large metal block that runs through a series of cycles of heating and cooling. In the prototype of the new device, the brainchild of Ugaz鈥檚 graduate student Nitin Agarwal, the sample tube surrounds three metal blocks held at different temperatures. When the fluid sample is heated it becomes less dense, making it flow upwards, while cooler fluid in another part of the loop moves downwards (Angewandte Chemie International Edition, DOI: 10.1002/anie.200700306). 鈥淚t鈥檚 a pump with no moving parts,鈥� says Ugaz, which cycles the DNA sample through the three temperatures needed for amplification.
The blocks are arranged in such a way that heating one ensures they all reach their required temperatures, so the device consumes very little power and can run on a pair of AA batteries.
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