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Essential Science: Fashioning green electrodes thanks to biology

By Tim Sandle     Jul 18, 2016 in Science
How can biological science help the electronics sector? The answer is bacteria helping to produce a new generation of nanoelectronic materials.
A new study has shown how a newly discovered strain of bacteria can effectively and consistently spin out extremely thin and highly conductive wires. The wires are composed of non-toxic, natural amino acids developed by scientists. The wires are the basis of the emerging field of nanoelectronics.
Nanoelectronics refers to the use of nanotechnology in electronic components. These items include hybrid molecular/semiconductor electronics, one-dimensional nanotubes/nanowires, and advanced molecular electronics. These developments follow a trajectory with computers: over recent decades computers have become more powerful as the transistors and semi-conductors have reduced in size; moving to the nanoscale is the next step in this process of shrinking electronic components. However, this creates a headache for scientists for as electronic devices approach the molecular scale, classical models for device behavior must be abandoned.
The field carries the promise of making computer processors more powerful; or offering enhanced memory storage; and leading to a new generation of optical devices and computer displays.
In a new development, scientists have developed a synthetic “biowire” to improve the electrical connections between two electrodes. This research has been led by microbiologist rather than physicists. Here a team in the laboratory of Dr. Derek Lovely (from University of Massachusetts at Amherst) has produced what are said to be thinnest wires ever created.
Remarkably the wires are manufactured from renewable, inexpensive feedstocks. The wires also avoid the harsh chemical processes typically used to produce nanoelectronic materials.
The microbial basis of the research is a bacterium called Geobacter, found in soil. Geobacter was found to be the first organism with the ability to oxidize organic compounds and metals including iron, radioactive metals and petroleum compounds. These can be converted into environmentally benign carbon dioxide through the use of iron oxide as an electron acceptor.
Electron diffraction pattern of an inorganic crystal  a tantalum oxide  2009.
Electron diffraction pattern of an inorganic crystal, a tantalum oxide, 2009.
Sven Hovmoeller (CC BY-SA 3.0)
Studies have also revealed that the bacterium can produce "microbial nanowires." These are electrically conductive protein filaments. In the soil environment, the nanowires enable the organism to grow on iron minerals.
While these natural nanowires had good conductivity, scientists realized that the conductive properties could be improved through genetic engineering. Here the researchers identified an amino acid (tryptophan) that was particularly key to the conductivity process used this to replace an amino acid in the bacterial cell. The researchers then rearranged the amino acids to produce a synthetic nanowire that was more conductive.
The outcome produced interesting results: the genetically engineered strain of Geobacter produced large quantities of the synthetic nanowires that were 2000 times more conductive than the natural biological product.
In a research note, Dr. Lovely explains the motivation for the research: “New sources of electronic materials are needed to meet the increasing demand for making smaller, more powerful electronic devices in a sustainable way.”
In terms of future applications, Dr. Lovely’s nanowires could be used in biocompatible sensors, computing devices, or as the components of solar panels.
In Florida individuals with solar panels can't sell the extra power they produce and solar comp...
In Florida individuals with solar panels can't sell the extra power they produce and solar companies are barred from selling any power that they generate -- unless they sell it back to the utility company
Kerry Sheridan, AFP
The research has been described in the journal Small. The research paper is titled “Synthetic Biological Protein Nanowires with High Conductivity.”
The news has intrigued the science community. Research center UMass Research Next (@ResearchNext) tweeted: "@UMassAmherst Scientists Engineer New Bacteria that Spins Out Tiny, Sustainable Nanowires." In addition, Philip Rossomando (@PhilipRossomand) posted: "Bacterial nanowires: 'Electric bacteria' not what we thought they were."
This article is part of Digital Journal's regular Essential Science columns. Each week we explore a topical and important scientific issue. Last week we considered the potential health benefits of drinking coffee. The week before we considered a new study that indicated how supplementing the diet of people, with metabolic syndrome, with resistant starch helps improve conditions like obesity.
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