Viruses
make tech materials
By
Kimberly Patch,
Technology Research NewsViruses cause the human population such trouble because the microscopic parasites adapt and reproduce so quickly.
Researchers at the University of Texas at Austin have shown they can take advantage of these viral strong points by harnessing billions of the phages to build useful materials molecule-by-molecule.
The researchers engineered a particular type of long, narrow virus to contain a peptide with an affinity for zinc sulfide nano crystals, and showed that under the right conditions a mixture of virus and crystals will build itself into a liquid crystal film.
A peptide is a component of protein. Liquid crystals are long chains of molecules that uniformly line up to form crystal-like structures under the influence of an electric field. The liquid crystals commonly used in computer displays, for instance, shift their orientation in response to changes in the surrounding electric field in order to change the color of individual pixels on a screen.
It should be possible to use viruses to build many other types of useful materials, said Andrea Belcher, an assistant professor of chemistry and biochemistry at the University of Texas at Austin. "So far we have peptides for about 20 different types of materials," including semiconductor, magnetic, optical, and biocompatible materials, she said.
The method could lead to considerably cheaper, faster and environmentally-friendly manufacturing processes for electronics.
The research is inspired by the way nature works, Belcher said. "Biology makes material at moderate temperatures using self assembly, self correction [and] non-toxic materials," and does this quickly, she said.
The difficult part of the process is finding particular proteins that can bind and assemble materials like semiconductors, said Belcher. The search for a protein to bind zinc sulfide took several months, she said.
"You have to choose proteins to work with, or evolve molecules to have the desired function. We have done a combination. We use a library of one billion different proteins and narrow down the ones that work the best," Belcher said. The challenge is "imagining the hard structure of the very small semiconductor nano particles and the soft structure of viruses at the same time," she said.
Once the researchers found the protein with the characteristics needed to bind to zinc sulfate, they inserted a bit of DNA into a virus's genetic material to add the protein to its coat.
And once they had the requisite virus, it was relatively easy to replicate. "Once we have a protein attached to a virus that we know does what we're interested in... we infect it into bacteria and make many millions of copies," Belcher said. This takes two or three days.
The researchers then made a virus and zinc sulfide liquid crystal suspension, and within a week the material assembled itself into uniform films, said Belcher. The films are ordered at the nanometer scale, extend to several centimeters, and are stable enough to be picked up by forceps, she said.
The virus measures 6.6 by 880 nanometers, and zinc sulfide nanoparticles are three nanometers in diameter. The peptide that binds to the zinc sulfide nano particles is on one end of the virus and is about 10 nanometers long. A nanometer is one millionth of a millimeter; three nanometers is about the size of 30 hydrogen atoms lined up in a row. One square centimeter of film contains about 40 billion viruses, said Belcher.
The exact structure of the film depends on the concentration of the viruses in the liquid crystal suspension and the strength of the surrounding magnetic field, said Belcher. The proteins that make up the virus's outer coat are weakly magnetic, which causes a growing virus-nanoparticle complex to align with a magnetic field. "Different types of liquid crystals can be made by changing these physical properties," she said.
One type of film the researchers made was ordered into domains, or patterns that spanned 0.07 millimeters and repeated continuously. Materials with such small-scale patterns could be used to make storage devices.
The exact mechanism the peptides use to attach to the zinc particles is not yet known, but is probably a combination of chemical interactions and shape, said Belcher.
The researchers are looking to make more types of materials using the same methods. "We're looking at these materials to grow and arrange electronic, magnetic and optical materials for devices, displays and sensors," said Belcher.
They are also developing biotechnology applications, she said. The researchers used a solvent to dissolve a piece of seven-month-old film, and found that the virus was still viable. "After storage at room temperature for seven months, [the virus] can be reinfected into a bacteria cell and amplified again," Belcher said. This reversibility makes it possible to use the film to store genetically engineered DNA, she said.
Using viruses to construct material is "absolutely novel... nobody has done this," said Viola Vogel, a professor of bioengineering at the University of Washington, and director of the school's nanotechnology center.
The work "combines elegantly what we've known about liquid crystals [and] what [Belcher] discovered about specific recognition of peptides and semi-conducting nanoparticles into making a totally new class of materials," she said.
Although it is relatively easy to make nanoparticle building blocks, using them to construct the many precise, patterned layers of nanoparticles that make up a material is potentially very difficult and tedious. "What is needed is a way to make materials where order is maintained from layer to layer to layer without putting in too much labor," said Vogel. This is one of the big challenges in the field of nanotechnology; "using viruses is just a very elegant way" of addressing it, she said.
Most of the research is still at the basic science stage, said Belcher. A few practical applications are possible within five years, but most applications will take 10 years or longer to develop, she said.
Belcher's research colleagues were Seung-Wuk Lee, Chuanbin Mao and Christine E. Flynn. They published the research in the May 3, 2002 issue of the journal Science. The research was funded by the Army Research Office, the National Science Foundation (NSF) and the Robert A. Welch Foundation.
Timeline: 5-10 years
Funding: Government, Institute
TRN Categories: Nanotechnology; Biotechnology; Materials Science and Engineering; Semiconductors
Story Type: News
Related Elements: Technical paper, "Ordering of Quantum Dots using Genetically Engineered Viruses," Science, May 3, 2002.
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May 15/22, 2002
Page One
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