Trapping particles, like DNA, is a first step to being able to analyze them, and there are different ways to catch them, such as using a nanopore or an optical tweezer. "It occurred to me, as a person who has spent my career doing nanofabrication, that the efforts to make small physical nanopores — about two to four nanometers [wide] — for DNA sequencing was going to be very difficult and extremely challenging to manufacture, get reproducibility [or] yield," says Mark Reed, a professor of engineering at Yale University. "It occurred to me to relax the geometry, but make the virtual pore size just as small with an electrodynamic trap."
Paul traps — developed by Wolfgang Paul, who won the 1989 Nobel Prize in Physics for this innovation — use oscillating electric fields to confine particles to a tiny, nanometer-scale space, and could offer advantages compared to other trapping methods. In an April Nanotechnology paper, Reed's team reported that alternating current traps, like Paul traps, stiffen as the particle size decreases. Optical tweezers, Reed adds, are very weak in comparison to Paul traps.
However, Paul traps had previously only been shown to work in a vacuum or a gaseous phase, not the aqueous phase that applications such as lab-on-a-chip assays or DNA sequencing would require. But in a June Proceedings of the National Academy of Sciences article, Reed and his colleagues used a charged polystyrene ball to show that aqueous Paul traps were possible. Indeed, they reported that their planar, aqueous device worked similarly to a conventional, linear trap. They added that their device could stably hold particles for up to four hours, and that they could change the size of the area in which the particle was held by altering the voltage and frequencies applied to the device. "It was gratifying to see that we could freeze the particle in the trap. With device dimensions of micron size, we were able to localize the particle to tens of nanometers," Reed says. "However, the most important accomplishment was clarifying and correcting some commonly held misconceptions. Until now, people had overlooked this."
The hope is that this technology could be used for diagnostics or in DNA sequencing — this work is supported by a National Human Genome Resources Institute's $1,000 Genome grant. While Reed says that Paul traps could be used now for large, micron-scale particles, they still need to be scaled down to the single molecule level to be used for DNA, and that's what his lab is currently tackling.