Researchers at the University of Twente, the Netherlands, have found that an electric voltage can be used to propel DNA molecules through a channel a few nanometres deep, or to stop them in their tracks. In a strong electric field the molecules judder along the channel, while in weaker fields they move more smoothly, enabling DNA fragments to be captured on a chip and separated for analysis.
When forced through extremely shallow channels just 20 nanometres deep and a few micrometres wide, DNA molecules behave very differently than they do in free solution. In the latter situation they tend to form clumps, while molecules in the channels are forced into an elongated straitjacket. This effect alone produces a difference in mobility between long and short molecules. Moreover, exposure to an electric field has now been shown to have a substantial effect.
This presents new options for the separation of fragments and entire molecules of DNA. The previous technique, known as gel electrophoresis, involved the use of micro-channels filled with a gel. According to researcher Georgette Salieb-Beugelaar, the laborious and time-consuming process of pouring in the gel can be rendered obsolete by the new method.
The researchers ascribe the difference in mobility to factors such as the roughness of the channel surface. A DNA molecule can easily be 1,000 times as long as the channels are deep. As a result, it encounters minute surface irregularities at many different points, an effect that is reinforced by the electric field. This seems to be the cause of the stagnation in mobility that occurs in strong fields. It presents an opportunity to capture fragments and – using weaker fields – to control their onward motion. This is the first demonstration of varying mobility in electric fields of differing strengths.
The study was conducted by the BIOS Lab-on-a-chip group, part of the MESA+ Institute for Nanotechnology at the University of Twente. The team included researchers at the University of Applied Sciences Wildau in Germany and the University of Lund in Sweden. The work partly financed by a grant from NanoNed, the Dutch nanotechnology network and Nano2Life, a European nanotechnology research network.