A DNA Walking Robot

By Roland Piquepaille

Two chemists from New York University, William B. Sherman and Nadrian C. Seeman, have created a DNA nanowalker with two legs, each one being 10-nanometers long. This nanoscale bipedal robot moves from one pair of anchors -- strands of DNA -- to another one. This is a major breakthrough for nanoscale manufacturing. And New Scientist says this opens the way for future nanoscopic robots that will assemble other nanomachines or manipulate individual molecules.

Because previous similar molecular-scale efforts have failed, what's the concept behind this breakthrough?

The New York team's biped can "walk" because its DNA-based legs are able to detach themselves from a DNA-based track, move along a bit, then reattach themselves.

Why DNA?

First, unlike other polymers, DNA chains like to pair up. However, two DNA strands will only "zip" together if the sequences of bases in each strand complement each other in the right way - so by tweaking the sequences chemists get a high degree of control over where each strand attaches. Second, researchers hope that cells can one day be engineered to manufacture these DNA-based machines.

Le's look at how this works.

Each of the legs in the walker is 36 bases long and is made from two strands of DNA that pair up to form a double helix. At the top, a springy portion of each DNA strand runs across from the left leg to the right, linking them together. At the bottom, one of the two strands pokes out of the helix to serve as a sticky foot.

The track, or "footpath", the walker travels on is also made of DNA, and is designed so that unpaired sections of DNA strands stick up like spikes along its length. These act as footholds for the walker. The feet attach to the footholds via "anchor" strands of DNA that match up with the foot sequence at one end and with the foothold at the other.

Because the left and right foot/foothold sequences are unique, each requires a different anchor. So to make the walker take a step, a free piece of DNA called an unset strand is introduced to peel away one of the anchors (see graphic), releasing the foot.

Here is a diagram showing how the nanowalker moves from a pair of anchors to the next one (Credit: Nano Letters)

Obviously, this is still at the experimental stage. Even the researchers don't say when such nanowalkers will be able to do some real work.

If you are a paying subscriber to Nano Letters, here is a link to the research paper which was published on April 22, 2004, "A Precisely Controlled DNA Biped Walking Device."

Source: Jenny Hogan, New Scientist, May 4, 2004