At this tiny scale, stuff can behave differently than at ordinary sizes. If small enough, the tools can even be affected by, and take advantage of, effects of quantum mechanics.

At the nanoscale, molecules such as DNA might be adapted to new uses, such as making tiny tweezers or molecular motors, as described by Bernard Yurke of Bell Labs during the annual meeting of the American Association for the Advancement of Science.

DNA is famous as the molecule that carries genetic information. DNA is a chain composed of four different types of links, or bases, called by the first letters of their chemical names: A, T, G, and C.

DNA can be a single long chain, called single-stranded DNA. The order or sequence of the As, Ts, Gs and Cs can be just about any order.

DNA can also be double-stranded, with the second strand being the complement to the first. It is double-stranded DNA that takes the famous helical shape of "DNA".

DNA can have double-stranded stretches interspersed with stretches of single-stranded DNA. The double-stranded stretches are more rigid and the single-stranded regions are more flexible.

Yurke and colleagues at Lucent and at the University of Oxford have described molecular tweezers made out of DNA that have two tips and a springy hinge. The tweezers are too small to be squeezed by human fingers. The tweezers are "squeezed" by adding a specific strand of single-stranded DNA, called an F strand for 'fuel strand', that specifically binds to a single-stranded region on the DNA tweezers. In going from single-stranded to double-stranded, the DNA contracts, and brings the two ends of the tweezers together.

The tweezers are released by adding a second type of single-stranded DNA, called an R strand for Release Strand, that competes with the tweezers for the F strand, removing the F strand and letting the tweezers open.

This open-and-shut approach is like a piston engine--it goes through specific steps that have to be timed and kept in the correct order: Add F strand, contract, add R strand, release, add F strand, contract, etc.

Using DNA to make tiny tools adds to the list of its uses. DNA is most familiar as an informational molecule. Researchers are also developing DNA as a chemical computer as an analogy to calculate answers to mathematical puzzles. DNA can carry electricity, and DNA may also prove useful in building new kinds of circuits for electrical computers. One way of looking at the DNA tweezers is as tailorable switches. Depending on the sequences of single-stranded regions, the tweezers might be specifically turned on or off (squeezed or released) by some F strands but not others. Since a switch is the basis for a computer, the DNA tweezers is just as likely to be used to pull out solutions to a puzzle as it is to pluck or move another molecule.

If the challenge is to build an engine to move stuff rather than to compute calculations, then the next step is to build a DNA motor that can continuously move and that eliminates the need for adding a release strand but rather requires only the addition of the fuel strand. This is like a treadle sewing machine, which converts the up and down motion of the sewer's foot into continuous spinning motion. Even better would be a tiny DNA molecular motor that spin continuously with only the addition of Fuel strands and without the need to add Release strands. This would be analogous to an electrical motor, which spins continuously with only the input of electricity, as compared to the step-wise cycles of the gasoline piston engine in which fuel and air are pumped in, exploded, and gasses exhausted.

www.bell-labs.com/project/feature/archives/dna/
UW-Madison research on DNA as chemical computer: www.news.wisc.edu/view.html?id=3542 
DNA Dance: A Model for Double-stranded DNA. http://www.biotech.wisc.edu/outreach/FunFoodStuff/dnadance.html 
This is DNA model you can build with yourself and 5 friends. (It's just like two teams lining up to shake hands after a hockey game.)