DNA assembly line: An atomic force microscope image shows gold nanoparticles on a DNA track.
Credit: Courtesy of Ned Seeman


The two machines, described in today's Nature journal, are a possible step forward in making DNA nanobots that could assemble tiny electrical and mechanical devices. DNA robots could also put together molecules in new ways to make new materials, says Lloyd Smith, a chemistry professor at the University of Wisconsin-Madison. "Robots might have the ability to position one molecule in a particular way so that a reaction happens with another molecule which might not happen if they randomly collide in solution," he says.


The nano walker made at Columbia University is a protein molecule decorated with three legs--single-stranded DNAzymes, synthetic DNA molecules that act as enzymes and catalyze a reaction. The legs bind to complementary DNA strands on a surface. Then they catalyze a reaction that shortens one of the surface strands, so that its attachment to the leg becomes weaker. That leg lets go and moves on to the next surface strand.

The walker follows a track of strands that the researchers pattern on the surface. It can take up to 50 steps--compared to the two or three steps taken by previous walkers. It stops when it encounters a sequence that cannot be shortened. "We show how to program [the walker's] behavior by programming the landscape," says Milan Stojanovic, a biomedical engineer at Columbia University who developed the walker. "It enables us to think about adding further complexity: more than one molecule interacting and more complicated commands on the surface. What we hope to do eventually is to be able to [use nanobots to] repair tissues."



The advances represent continuing success in creating nano devices with increasingly complex functions. "[We're] moving from individual entities that do something interesting to systems of entities working on something with a more complex behavior and function," Smith says.

Copyright Technology Review 2010.