In efforts to create motors and other machines on the scale of molecules — machines that can act as tiny assembly lines to make novel compounds — the devices have to walk before they can run. And when it comes to walking, molecular machines have to be able to do so on their own, in the proper direction. Most molecular walkers need some help, in the form of chemicals to keep them going, and they tend to wander.
Researchers at New York University and Harvard have created a two-legged walker, made from a strand of DNA, that solves both of those problems — it walks on its own in one direction along a track, also made of DNA strands.
Nadrian C. Seeman, a professor at N.Y.U. and the author, with Tosan Omabegho and Ruojie Sha, of a paper in Science describing the work, said one key to their walker’s autonomy is that binding the forward part of the DNA strand — the leading “leg” — to the track releases a chemical that catalyzes the release of the trailing “leg,” which then dangles forward and binds with the track again. This synchronized two-step process, which covers about fifty-billionths of a meter, should be repeatable for any length of track, Dr. Seeman said.
The idea behind making walkers, he added, is to emulate motor proteins like kinesin, which carry large molecules around a cell. Walkers would carry a similar molecular “cargo” down the track that would react with other molecules at various points. The final product, at the end of the track, would depend on what those other molecules were.
Conceptually, Dr. Seeman said, it’s not all that different from a car assembly line, where the initial components travel along a track and other components are added on along the way. A walker would be a chemical assembly line, he said, “making things that haven’t been made before.”