Again, just a few bases are allowed to hang unpaired, which permits a fifth strand to rip away the first fuel unit and open the tweezers. It's clever in the way the tweezers are self-assembled in the first place, and, secondly, in the way they are powered. It is trivial to design DNA sequences that are complementary. The tricky bit is making sure the bits that aren't supposed to stick together don't. So it was basically done by screening different sequences to ensure the interactions that weren't desired were minimised.
Nature is a thousand times smaller again.
Scientists are very keen to exploit the interesting and sometimes unusual properties that arise in materials when their constituent atoms or molecules are precisely arranged. They believe nanotechnology also offers the possibility of making electronic circuits yet smaller and more powerful. But it is extremely difficult, not to say expensive, to build on the nanoscale. Hence, the search for special tools that can do the job. The Bell Laboratories are already working to attach DNA to electrically conducting molecules to assemble rudimentary molecular-scale electronic circuits.