Synthetic biowire are making an electrical connection between two electrodes. Researchers led by microbiologist Derek Lovely at UMass Amherst say the wires, which rival the thinnest wires known to man, are produced from renewable, inexpensive feedstocks and avoid the harsh chemical processes typically used to produce nanoelectronic materials. Credit: UMass Amherst
A genetically designed strain of bacteria spins out very thin and highly conductive wires made up of solely of non-toxic, natural amino acids. Researchers led by microbiologist Derek Lovely say the wires, which rival the thinnest wires known to man, are produced from renewable, inexpensive feedstocks and avoid the harsh chemical processes typically used to produce nanoelectronic materials. The ability to mass-produce such thin conductive wires with this sustainable technology has many potential applications in electronic devices, functioning not only as wires, but also transistors and capacitors. Proposed applications include biocompatible sensors, computing devices, and as components of solar panels.
This advance began a decade ago, when Lovley and colleagues discovered that Geobacter, a common soil microorganism, could produce “microbial nanowires,” electrically conductive protein filaments that help the microbe grow on the iron minerals abundant in soil. These microbial nanowires were conductive enough to meet the bacterium’s needs, but their conductivity was well below the conductivities of organic wires that chemists could synthesize. Lovley said: “We knew that one class of amino acids was important for the conductivity, so we rearranged these amino acids to produce a synthetic nanowire that we thought might be more conductive.”
The trick they discovered to accomplish this was to introduce tryptophan, an amino acid not present in the natural nanowires. It is also highly effective at the nanoscale in transporting electrons. “We designed a synthetic nanowire in which a tryptophan was inserted where nature had used a phenylalanine and put in another tryptophan for one of the tyrosines.” says Lovley. The results greatly exceeded the scientists’ expectations. They genetically engineered a strain of Geobacter and manufactured large quantities of the synthetic nanowires 2000X more conductive than the natural biological product. An added bonus is that the synthetic nanowires, which Lovley refers to as “biowire,” had a diameter only half that of the natural product.
“We were blown away by this result,” says Lovley. The conductivity of biowire exceeds that of many types of chemically produced organic nanowires with similar diameters. The extremely thin diameter of 1.5 nm (>60,000 times thinner than a human hair) means that thousands of the wires can easily be packed into a very small space. Although the biowire is made out of protein, it is extremely durable. In fact, Lovley’s lab had to work for months to establish a method to break it down.
“It’s quite an unusual protein,” Lovley says. “This may be just the beginning” he adds. Researchers in his lab recently produced more than 20 other Geobacter strains, each producing a distinct biowire variant with new amino acid combinations. He notes, “I am hoping that our initial success will attract more funding to accelerate the discovery process. We are hoping that we can modify biowire in other ways to expand its potential applications.” http://www.umass.edu/newsoffice/article/%E2%80%98green%E2%80%99-electronic-materials-produced
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