NANO-FACTORIES of the future could be equipped with DNA strands acting as nanoscale robot arms that will pick up and assemble molecular-scale objects.
Such long-sought nanorobots are now a step closer thanks to a team led by Nadrian Seeman of New York University in New York City, which has built a machine in which a DNA arm is attached to a body that is also made of DNA. The researchers were then able to make the arm move back and forth by washing the whole structure with a solution containing fragments of DNA that bind to different parts of the main body.
In future, similar DNA structures could be used to form a miniature assembly line in which the robotic arms move in co-operative waves like the legs of an upturned centipede. The arms could be used to bring molecules together in specific orientations that cause them to react chemically with each other in unusual ways, yielding different chemicals from those produced when the molecules encounter each other randomly. 鈥淭his may enable us to make things we cannot make any other way,鈥� Seeman says (Science, vol 314, p 1583).
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DNA strands are an attractive option as components of nanoscale structures because of the way they lock or 鈥渮ip鈥� together when the sequence of bases in a pair of strands complement each other. Seeman has exploited this in the past to create branched DNA structures which unzip when washed with a solution of a different, suitably tailored DNA fragments (快猫短视频, 8 May 2004, p 22). Before these could be used as construction tools, however, some way had to be found to control their positions and motion with respect to each other, to allow hundreds of machines to work together in an assembly line.
Seeman has now figured out that this can be done by attaching the DNA machines to a surface that defines their positions. 鈥淭his is something that has been on the wish list for a while,鈥� says biochemist William Shih of Harvard University.
The surface is made out of hundreds of DNA tiles that join up automatically to form a repeating pattern. There are eight different types of tile, each made of three intertwined strands of DNA, but only one type of tile has an extra unpaired DNA strand that is complementary to an unpaired strand on the base of the DNA machines. This ensures that the machines only bind to one type of tile, so they end up dotting the surface in predictable locations at predefined distances from each other.
Each DNA machine consists of a long, slender body and an attached DNA 鈥渁rm鈥� that sticks out from it at right angles. Washing them with a particular DNA fragment causes a portion of their body to unzip, allowing a second DNA fragment to attach itself. This fragment takes the place of the first, but has a different shape, causing the body to rotate and to drag the arm with it.
For now, all the DNA machines are identical so they all respond in the same way to DNA washes, causing the arms to move in unison. Seeman is now working on arms that can be individually controlled.
