|By Curt Suplee
Washington Post Staff Writer
Thursday , June 8, 2000 ; A02
The same trick an oyster uses to make mother-of-pearl may ultimately enable researchers to "grow" ultra-miniaturized computer chips.
The electrical pathways would be self-assembled like the delicate whorls of seashells, rather than etched by conventional manufacturing techniques, and would be only a fraction the size of the smallest circuit components possible today.
That is the hope of a team of scientists who have discovered that tiny protein-like strands on the surface of common viruses--the sort of molecules that enable germs to identify and grasp their target cells--also bind tightly and very selectively to materials widely used in high-tech electronics, such as silicon and gallium arsenide.
Once attached to such substances, the researchers suspect, a viral molecule could serve as a template or skeleton for the growth of super-thin threads of semiconductors.
In the same way, proteins secreted by oysters or abalones control the arrangement of calcium compounds to create the animals' shells, and cells embedded in a mineral matrix direct the construction of bone.
"It's the first step in integrating biological molecules and inorganic molecules that have technological importance," said chemist Angela M. Belcher of the University of Texas at Austin, whose team reports its findings in today's issue of the journal Nature.
The work "represents a major technological breakthrough in the field of nanotechnology"--the science of building things at the scale of nanometers, or billionths of a meter--that "will lead to a whole new class of nanoscale sensors," said Gary L. Harris, director of Howard University's section of the National Science Foundation's National Nanofabrication Users Network.
Nanoscale assembly has become an urgent issue because engineers are running out of ways to shrink and speed up computer processors to create the next generation of chips.
For the past 30 years, the number of electronic devices that can be packed onto a fingernail-sized strip of silicon has approximately doubled every year--raising computing power exponentially and boosting the U.S. economy along with it.
But now that trend may be reaching its limit. Intel's Pentium III processor contains 28 million transistors, thanks to the ability to etch electrical connections that are only 180 nanometers wide. Many experts say that must shrink to 100 nanometers by 2005; further reductions by conventional methods, however, appear daunting, if not impossible.
So researchers are looking at a host of potential alternatives. Belcher and colleagues set out to see whether viral surface molecules called peptides--which are only about 15 nanometers long and superbly well-adapted to identifying specific organic sites--would be equally selective in binding to key non-biological substances such as semiconductors.
The team started with hundreds of millions of viruses, each bearing a different peptide, and exposed them to various semiconductor crystals. After an hour, the researchers washed off the viruses that didn't bind to the crystal, or that bound only weakly. The remaining viruses were separated and then cloned in cell culture, increasing their numbers a millionfold. This process was repeated several times until the scientists finally isolated precisely those viruses that targeted only specific semiconductor crystals and attached very firmly.
The finicky molecules were remarkably selective: Some would bind to one crystalline form of gallium arsenide, but not to another similar arrangement of exactly the same compound. One peptide was able to discriminate between two nearly identical crystals in which the atomic spacing differed by only 0.01 angstroms, or one-trillionth of a meter.
Such "biocomposite" materials, the team wrote in Nature, "should provide powerful building blocks for the fabrication of a new generation of complex, sophisticated electronic structures."
It remains to be seen whether that is possible, although similar nanoassembly processes are familiar in biology. "We're borrowing ideas from nature," said Belcher, who did her PhD work on the formation of seashells. "Proteins are known to control crystal structure in shells. But nature stopped at calcium carbonate and calcium phosphate," compounds abundant in seashells. "We focus where nature left off."
Eventually, Belcher said, her team is hoping to "be able to integrate living cells and electronic materials for neuroprosthetics" that could substitute for damaged nerve systems, and to "explore ways of building connections between electronic components for faster communication" either electronically or optically.
"The ability to pattern such small interconnections . . . is one of the big tasks for electronic industry today," said Sandip Tiwari, director of the Cornell Nanofabrication Facility at Cornell University. At present, "we do not have the techniques for defining features at these dimensions," he said. If the Texas results prove workable, "and if we can find the right small electronic devices with the right properties and reproducibility, we would have made big progress in harnessing the power of nanoelectronics."
Although the research is still at a preliminary stage, Chad A. Mirkin and T. Andrew Taton of the Center for Nanofabrication and Molecular Self-Assembly at Northwestern University write in an accompanying commentary in Nature, "this approach is likely to become a powerful technique for the design of materials in years to come."
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