Thursday, March 16, 2006

Do-It-Yourself Nanotech

Continued from page 1

By Kevin Bullis

Right now, though, the technique is a solution in search of the problem. But Rothemund and others, such as Shih, expect practical applications to come soon, as researchers learn how easy the technique is and find ways to apply it to specific problems. One possibility is patterning electronic devices at a smaller scale than is possible using today's optical lithography methods. Thomas LaBean, a chemist and computer scientist at Duke University, who has developed another general-purpose DNA self-assembly technique that is a bit more difficult and has a lower resolution than Rothemund's, is developing single-electron transistors patterned with DNA that could serve as components for such a device.

There are significant challenges remaining, however, before working devices using this method appear. "With self-assembly, there is an inherent error rate," says Harvard's Shih. Unlike today's computers, for example, self-assembled computers will need to detect and work around non-functioning components. Also, many applications will require bigger patterns than Rothemund has made so far. One potential solution to that problem, which Rothemund has tried already with limited success, is combining smaller shapes using strands of DNA, much as cells come together to build an organism, he explains.

Also, while the new technique is affordable for labs, it is not yet cheap enough for making bulk materials. The self-assembly already demonstrated, however, could be practical for building "nanoarrays" that can measure the precise contents of single cells, Shih says, allowing biologists to better learn the roles played by individual cells, for example, those in a nervous system.

In fact, the best application may not yet have been thought of. "I don't feel discouraged that we haven't found the super-killer applications for this yet," says Shih. "Being able to assemble trillions of molecularly precise devices is something we have just not been able to do. And now suddenly we have this method where we can do that, for an affordable price. It's not obvious what those payoffs will be, but we all feel like they're there."

Lloyd Smith, a chemist from University of Wisconsin, Madison, and author of a commentary on the work in Nature, wrote, "We are now perhaps more limited by our imagination than our ability."