Nature nurtures nanotechBy Kimberly Patch, Technology Research News
Taking a cue from seashell construction, University of Texas researchers are harnessing natural growth processes to make tiny biocomposite building blocks that engineers could one day use to build nanoscale electronic devices.
Using a stock of 100 million viruses engineered to include various peptides as part of their protein coats, researchers isolated several whose peptides were able to combine well with semiconductor materials gallium arsenide, silicon, indium phosphides and zinc selenide.
The idea was inspired by the way nature makes materials, said Angela M. Belcher of UT Austin’s department of chemistry and biochemistry and the UT Austin Texas Materials Institute.
Shell and bone are constructed of a combination of organic and inorganic materials and can be up to 90 percent inorganic. Belcher is finding organic materials that have affinities for inorganic materials that are not generally used by living organisms but are useful to the electronics industry -- like semiconductors and magnetic and optical materials.
"Abalones grow shells [by using] nanostructures of calcium carbonate with perfect precision. It seemed [logical] to see if we could harness some of that same potential... to assemble materials that may be technologically important,” said Belcher, whose research team includes Sandra R. Whaley, Paul F. Barbara and Douglas S. English.
Building electronic components this way has two distinct advantages. First nature's "amazing ability to assemble on a very small scale" addresses looming size limitations in current semiconductor manufacturing, said Belcher.
Second, natural processes make for very skilled building. "Nature's precise, and were trying to be able to capture that amount of precision," she said. "What we've proven by these experiments is that we can have a precision over selecting one crystal versus another on the same level that has evolved in organisms."
"It's very interesting stuff -- a lot of important things are going to come out of coupling natural systems and inorganic systems," said Mark Thompson, professor of chemistry at the University of Southern California in Los Angeles. "Instead of having to build [nanostructures one molecule] at a time, she can build viruses [to do] the assembly work, and the piecing together work."
Viruses are also "easy to grow and replicate and we know a lot about the structures of viruses and how to manipulate viruses," Thompson added
To isolate the viruses that were able to combine with the semiconductors, Belcher and her colleagues went through several generations of experiments, selecting for a tight bond between a virus's peptides and an inorganic material, and for "clean specificity," meaning that the viruses were able to pick the right material and reject similar materials.
They also found viruses that bound only to a specific crystal structure and rejected the same material when it was structured differently. Different crystal faces of gallium arsenide, for example, are chemically different. "They're all made out of gallium and arsenic, but on different faces the atoms are arranged differently, and our peptides can recognize specific faces," Belcher said.
The semiconductor experiments selected for a tight bond, but another potentially useful trait for natural particle manufacture is an ability to drop the material at a certain time, so the researchers are also working with virus strains that show various gripping abilities. Too strong a bond, for instance, may hinder an application that uses peptides to deliver nanoparticles to a particular area of a wafer, said Belcher.
In addition, the researchers are working with viruses that can grow semiconductor nanoparticles. "We eventually want to... not only bind particles and move them around, but grow particles from solution. And so we are [selecting] for things that nucleate, or grow small particles exactly where you want them," Belcher said.
The researchers are also working with magnetic and optical materials to find peptides with an affinity for those materials, Belcher said.
Belcher and her colleagues ultimately hope to provide a set of proteins useful for integrating the biocomposite materials into electronic devices. "Were trying to develop tool kits that can be used to assemble materials," she said. The practical application of this research to manufacturing is probably at least 10 years away, she added.
Funding for the project came from the Defense Advanced Research Projects Agency, the National Science Foundation, the Robert A. Welch Foundation, the University of Texas Austin, and a Du Pont Young Investigator Award. A paper on the researchers' work on peptides and semiconductors was published in the June 8 issue of Nature magazine.
Timeline: >10 years
Funding: Corporate, Government, Private and University
TRN Categories: Nanotechnology; Semiconductors and Materials
Story Type: News
Related Elements: Photo; Technical paper in Nature, June 8, 2000, p. 665
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