Available online 29 September 2011.
Scientists from the University of Massachusetts at Amherst in the United States have uncovered new conducting properties in nanowires produced by bacteria called Geobacter sulfurreducens, which allow electrons to travel longer distances and could lead to cheaper and less toxic nanomaterials for biosensors and solid-state electronics that interface with biological systems.
The team of both physicists and microbiologists, whose work was published in Nature Nanotechnology [Malvankar et al. Nature Nanotech (2011) doi: 10.1038/nnano.2011.119], revealed that microbial nanowires, networks of bacterial filaments, can transport a charge through biofilms in the same way as synthetic organic metallic nanostructures. However, this previously unknown property of microbial nanowires means they can do this over much longer distances, many times the length of the bacterium.
As lead microbiologist Derek Lovley points out “The ability of protein filaments to conduct electrons in this way is a paradigm shift in biology and has ramifications for our understanding of natural microbial processes as well as practical implications for environmental clean-up and the development of renewable energy sources.”
The team had previously shown that Geobacter nanowires could represent a fundamentally new biological behavior; however, as they did not have a suitable mechanism at that time, the theory did not find popularity. To continue their research, they replaced the iron oxides with electrodes. On the electrodes, the Geobacter produce thick and electrically conductive biofilms. The team therefore realized that the metallic-like conductivity of the biofilm was due to a network of nanowires that spread across the biofilm.
It is known that artificial nanowire properties can be altered by changing their surroundings; however, using the natural properties of Geobacter means that the team can manipulate their electrical properties just by changing the temperature or regulating gene expression. The Geobacter can also create natural materials that are more environmentally friendly and cheaper than man-made materials. This could be a significant advantage, as many current nanotech materials are expensive to produce, primarily due to the need for rare elements in their manufacture.
The metallic-like conduction of electrical charge along a protein filament has also not been shown before, and it was previously believed that the conduction required a series of proteins called cytochromes, which electrons could jump between. However, this study has shown that long-range conduction is possible without cytochromes, with the Geobacter filaments acting as a wire.
As lead physicist Mark Tuominen stated, “This discovery not only puts forward an important new principle in biology but in materials science. We can now investigate a range of new conducting nanomaterials that are living, naturally occurring, nontoxic, easier to produce and less costly.”
Volume 14, Issue 10, October 2011, Pages 459