Smallest Robot

Seeman was inspired to begin building with DNA in a bar in Albany, New York, in the fall of 1980, where he was working as an X-ray crystallographer. Sitting in the bar, he realized that the flying fish in a familiar woodcut by M.C. Escher were similar to a DNA molecule with six branches. To Seeman, Escher's image, which now hangs in his NYU office alongside intricate knots and posters of DNA, was familiar from his crystallography work. Escher's picture shows "a whole bunch of flying fish that look just like a jack, a six-armed junction arranged like the molecules in a crystal."

Over the next two decades, Seeman has been using DNA to make intricate structures that resemble elaborate crocheting, including a cube and a truncated octahedron. Last year, as reported in the Journal of the American Chemical Society, he and his team were able to "knit" nylon with DNA. "What we are trying to do is to control the structure of matter on a very small scale, to actually design molecules on the most fundamental levels, and then get them to assemble into specific three-dimensional molecular structures." To do that, Seeman takes advantage of the fact that DNA's two strands like to pair up with other strands, the a zipper's tracks do, but only if the sequences of bases in each strand are complementary. "If DNA can do so, it will form these complementary helices at all sites that are available to it," says Seeman, "and these double helices are very predictable. If we know what's on one strand, we know what's on the other strand." By controlling the sequences, the chemists can control where each strand attaches.

DNA image: Drew Berry, The Walter and Eliza Hall Institute of Medical Research

Once Seeman and Sherman's tiny biped is able to take more than a couple of steps, it could "man" a molecule-sized assembly line. "I believe we can make molecular-level assembly lines to do the same sort of things that are made on a human scale," says Seeman. "Ultimately I think this will lead to nano-manufacturing, or 'nanofacturing', where we can take a molecule and move it along, just like a car on an assembly line in Detroit. And just the way a car reaches a certain point and a spot welding robot comes down and works on it, our nanoscale robot can do some chemistry on a molecule. Then the molecule can move on, and at the next point where we need more chemistry, the same thing can happen."

But first, the researchers have to figure out how to make their tiny robot carry something, like a single atom. This research appeared in the journal Nano Letters and is funded by the National Science Foundation (NSF), the National Institute of General Medical Sciences, the Office of Naval Research (ONR), the Defense Advanced Research Projects Agency (DARPA), and the Air Force Office of Scientific Research (AFOSR).