Post by whiterose on Oct 21, 2007 9:56:00 GMT -5
Virus-Built Electronics
www.technologyreview.com/Nanotech/19503/page1/
Virus-Built Electronics November/December 2007
Virus-Built Electronics
Assembling nanomaterials with the help of innocuous viruses could lead to threadlike ¬batteries and photovoltaics that can be woven into clothing.
By Kevin Bullis
Tiny building blocks: A small vial contains a billion viruses, each with a slightly different genetic modification. These can be screened to determine which of them will bind to specific inorganic materials, such as those used in rechargeable batteries.
Credit: Porter Gifford
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Angela Belcher leans in to watch as a machine presses down slowly on the plunger of a syringe, injecting a billion harmless viruses into a clear liquid. Instead of diffusing into the solution as they escape the needle, the viruses cling together, forming a wispy white fiber that's several centimeters long and about as strong as a strand of nylon. A graduate student, Chung-Yi Chiang, fishes it out with a pair of tweezers. Then he holds it up to an ultraviolet light, and the fiber begins to glow bright red.
In producing this novel fiber, the researchers have demonstrated a completely new way of making nanomaterials, one that uses viruses as microscopic building blocks. Belcher, a professor of materials science and biological engineering at MIT, says the approach has two main advantages. First, in high concentrations the viruses tend to organize themselves, lining up side by side to form an orderly pattern. Second, the viruses can be genetically engineered to bind to and organize inorganic materials such as those used in battery electrodes, transistors, and solar cells. The programmed viruses coat themselves with the materials and then, by aligning with other viruses, assemble into crystalline structures useful for making high-performance devices.
But the approach is not just an alternative way to make familiar devices; it could also be the impetus for developing entirely new ones. In past work, Belcher has created virus-based thin films for rechargeable batteries. Now that she can spin viruses into fibers, she envisions threadlike batteries and other electronic devices that can be woven directly into clothing. "It's not really analogous to anything that's done now," she says. "It's about giving totally new kinds of functionalities to fibers."
The virus-based fibers have caught the attention of U.S. Army researchers. They hope to incorporate future versions of the fibers into uniforms, weaving them into the fabric along with other supporting materials. The resulting fabrics could have an array of advanced capabilities. Clothing made with them could sense agents of chemical and biological warfare; it might also store energy from the sun and power portable electronic devices, such as night-vision gear. Charlene Mello, a macromolecular scientist at the Natick Soldier Research, Development, and Engineering Center in Natick, MA, says that while such uniforms will probably take decades to develop, Belcher's work has paved the way for them.
Spinning Viruses
Belcher uses different procedures to make different kinds of virus fibers. To make the glowing fibers, she first used conventional genetic-engineering methods to modify the virus DNA so that one of the proteins that make up the body of the virus has extra copies of a specific amino acid at one end. At the same time, the researchers synthesized quantum dots (semiconductor nanocrystals that emit intense light at precisely tuned wavelengths) with surface amine groups that bind to the overproduced amino acid. The result: hundreds of quantum dots glommed onto each virus, which combined with similar viral particles to form a fiber that emits light.
Often, however, it's not obvious how to make a virus bind to specific inorganic materials, such as gold particles. In these situations, Belcher uses a method sometimes called "directed evolution," which allows her to quickly modify viruses to work with a range of materials.
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Assembling nanomaterials with the help of innocuous viruses could lead to threadlike ¬batteries and photovoltaics that can be woven into clothing.
By Kevin Bullis