Texas A&M researchers have devised a prototype polymerase chain reaction (PCR) device for the rapid and affordable replication of DNA samples. The tubular device creates a perpetual flow of fluid and DNA from hot denaturing zones, to cool renaturing zones similar to a lava lamp.
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.