make tech materials
Technology Research News
Viruses 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,"
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
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,"
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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