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ARGONNE, NASA-AMES RESEARCHERS BUILD NEW BIOLOGICAL MACHINES
Working with colleagues from NASA and the SETI Institute, the researchers built bioengineered nanoscale arrays, using genetically engineered proteins as templates to create honeycomb-like patterns of gold and a semiconducting material. Each cell in the array is just 20 nanometers (billionths of a meter) across, 5,000 times smaller than the width of a human hair. Current lithographic techniques that produce similar arrays are limited to about 100 nm. "Nanofabrication is all about making very small things better, faster and more simply," said Nestor Zaluzec, who heads Argonne's Telepresence Microscopy Laboratory. "Biological systems can self-organize and do much of the work by themselves." The research team included principal investigators Jonathan Trent and Andrew McMillan of NASA's Ames Research Center, who performed their research at Argonne without leaving their home base in California. The NASA-Ames researchers began by isolating a protein from Sulfolobus shibatae, a bacterium that lives in geothermal hot-springs and can tolerate near-boiling temperatures and high acidities. Trent and McMillan genetically modified an S. shibatae protein to create a chemically active site on its edge. The protein was cloned into a harmless form of Escherichia coli bacteria, which can be grown easily in vats. Heating the resulting brew destroyed the E.Coli proteins, allowing the team to isolate large amounts of the heat-tolerant Sulfolobus protein. The purified protein naturally forms ring-shaped structures just 10 to 20 nanometers across, called chaperonins. The chaperonins were then applied to substrates such as silicon wafers, where they self-assembled into large, hexagonal, periodic patterns. The scientists added a slurry of nanoparticles of gold or a semiconducting material called cadmium selenide-zinc sulphide. The materials would adhere only to active sites around the hole in each protein ring. The resulting precise, regular arrays of nanoparticles closely resemble similar patterns used in the microelectronics industry, only much smaller. Such arrays of nanoparticles could have future applications in computer memories, sensors or logic devices. Zaluzec, a longtime associate of Trent, led the nanoscale characterization effort of the research by coordinating state-of-the-art analytical electron microscopy of the biologists' samples. Trent and McMillan in California could literally and figuratively watch over Zaluzec's shoulder in Illinois as he magnified their samples up to 10 million times using the electron microscope. The Telepresence Microscopy Laboratory is wired with video cameras accessible via the Internet to facilitate collaboration and analysis with researchers just about anywhere in the world. "Jonathan and Andrew never set foot in the microscope room," Zaluzec said. "But we could collaborate in real time, which was important to our success." The team is now working to expand the range of chemical activity of the proteins, which may allow them to create self-organizing templates of different types of materials, and to control the size and spacing of the underlying protein template. "This process reaches a dimensionality not readily accessible in materials science," Zaluzec said. "At these sizes, there are sometimes novel effects in materials and their electronic, magnetic and optical properties. These templates give us a chance to explore these effects."
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