Self-assembly comes together

When it comes to assembling molecules into complex structures, materials scientists have been outclassed by nature. Compare, for example, chemists and clams. Both make high-strength ceramic composites. But while chemists must rely on crude methods--including extreme temperatures and the use of molds--to fuse neighboring molecules into specific shapes, certain clams take a more elegant approach. These mollusks engineer a shiny, tough mother-of-pearl shell by using a series of proteins that assemble themselves into a scaffolding. The scaffolding guides tiny ceramic plates, created by the mollusk, into precise shell layers.

Materials scientists would love to be able to emulate the clam and duplicate this type of "self-assembly," because it offers tremendous advantages in control and economy over conventional manufacturing. To control the makeup of microchips, for example, manufacturers need billion-dollar plants with clean rooms and vacuum chambers. Self-assembled structures, on the other hand, simply put themselves together based on attractive and repulsive forces between molecules. And the apparatus for doing this type of self-assembly--essentially a beaker on a tabletop--"costs about a dollar," says Tom Mallouk, a chemist at Pennsylvania State University.

So, hoping to borrow from biology, materials scientists are increasingly attempting to use materials that make themselves. Indeed, the growing use of self-assembly is part of what chemist Stephen Mann of the University of Bath in England calls a "quiet revolution" in materials science. The revolution, says Davis, is "the most important thing in materials synthesis right now. Biological organisms already know how to do this with unbelievable sophistication. They can organize structures at the angstrom, micron, and centimeter level. We're still at the beginning stages. But we're learning fast."

Although scientists are nowhere near duplicating nature's more elegant self-assemblies, they are already beginning to register their first practical successes. Several drug companies are in late-stage clinical trials with self-assembled microscopic vesicles that ferry potentially lifesaving drugs to cancer patients. And by getting organic, metal, and phosphonate molecules--complexes of phosphorus and oxygen atoms--to assemble themselves into conducting materials, researchers are turning electronic fabrication into a benchtop affair.

For now, most of this work remains in the early stages, particularly for electronics. Though most self-assembly setups are cheap by the standards of the semiconductor industry, they face stiff competition from existing technology, which has decades of...