Caltech scientists control complex nucleation processes using DNA ori...( PASADENA Calif.--The construction of...)

PASADENA, Calif.--The construction of complex man-made objects--a car, for example, or even a pizza--almost invariably entails what are known as "top-down" processes, in which the structure and order of the thing being built is imposed from the outside (say, by an automobile assembly line, or the hands of the pizza maker).

"Top-down approaches have been extremely successful," says Erik Winfree of the California Institute of Technology (Caltech). "But as the object being manufactured requires higher and higher precision--such as silicon chips with smaller and smaller transistors--they require enormously expensive factories to be built."

The alternative to top-down manufacturing is a "bottom-up" approach, in which the order is imposed from within the object being made, so that it "grows" according to some built-in design.

"Flowers, dogs, and just about all biological objects are created from the bottom up," says Winfree, an associate professor of computer science, computation and neural systems, and bioengineering at Caltech. Along with his coworkers, Winfree is seeking to integrate bottom-up construction approaches with molecular fabrication processes to construct objects from parts that are just a few billionths of a meter in size that essentially assemble themselves.

In a recent paper in the Proceedings of the National Academy of Sciences (PNAS), Winfree and his colleagues describe the development of an information-containing DNA "seed" that can direct the self-assembled bottom-up growth of tiles of DNA in a precisely controlled fashion. In some ways, the process is similar to how the fertilized seeds of plants or animals contain information that directs the growth and development of those organisms.

"The big potential advantage of bottom-up construction is that it can be cheap"--just as the mold that grows in your kitchen does so for free--"and can be massively parallel, because the objects construc
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