Scientists sponsored by the Office of Naval Research (ONR) and headed by Dr. Derek Lovely have genetically modified a common soil bacteria to create electrical wires that not only conduct electricity, but are thousands of times thinner than a human hair.
The soil bacteria used in the study is Geobacter, which has tiny hair-like protein filaments protruding from the surface that functions as electrical wires. Geobacter establishes its electrical connections with iron oxide in the ground that in turn supports its growth. The Geobacter inherently carries electricity sufficient for its sustenance and the electricity produced is enough to be measured with electrodes; however, not enough for human use.
It is notable that Geobacter was first isolated by Dr. Derek Lovely in 1987 and was characterized as a strict anaerobic, metal-reducing bacteria.
“As we learned more about how the microbial nanowires worked, we realized it might be possible to improve on nature’s design” said Dr. Lovely.
To achieve the target of improving the electrical conductivity of microbial nanowires, the team tweaked the genetic code of the bacteria. Two amino acids existing naturally in the wire were replaced with Tryptophan– an amino acid with great ability to transport electrons at nanoscale.
This genetic modification enhanced the synthetic nanowire conductivity by 2,000 times compared with the unmodified soil bacteria’s electrical conductivity. The diameter of nanowires was found to be 1.5 nanometers, which is over 60,000 times thinner than human hair. Furthermore, the nanowires were found to have enhanced durability vis-à-vis the naturally occurring counterpart.
“We rearranged the amino acids to produce a synthetic nanowire that we thought might be more conductive,” said Dr. Lovley.
The synthetic microbial nanowire is a noteworthy contribution to the increasing demand of device miniaturization for shrinking electronics. Device miniaturization lessens the raw materials consumed in the production and benefits the mass production of more powerful devices. In this regard, these thin synthetic microbial wires can be fitted in smallest possible spaces and can be used for smaller devices.
Additionally, Geobacters can survive on almost any kind of plant waste and can be raised on carbon dioxide and renewable energy sources. Opting for the biological source for electrical wire synthesis ensures sustainability, and eliminates the hazardous chemicals and components involved in the process and the final product.
With the overwhelming breakthrough, the microbial nano-wire is foreseen as marriage between the biology and electronics catering to wide-range of applications. Dr. Lovley believes that these microbial wires could be used to produce bio-transistors and bio-capacitors and can constitute solar panels, computing devices and biosensors.
Being funded by ONR, the first potential application is in military. In remote locations of war zones, delivery of shipping fuel is done in convoys, which is an expensive and risky affair. These microbial nanowires could be fed to modified micro-organisms to produce alternative fuel thereby minimizing the dependence of troops on conventional fuels.
Other set of applications could be as sensors. For instance, they can power the sensitive microbes fixed on unmanned vehicles for detection of contaminants, toxins or explosives. They can also be used to monitor heart rate or kidney functions in medical industry. Furthermore, Dr. Lovley mentioned that the conductivity of Geobacter’s filaments is highly dependent on the acidity of the environment. This property makes the nanowire suitable for using them as pH biosensor for conditions with varying acidity (e.g., certain diseases in human body).
After all, it’s just the beginning.
The original work can be accessed here.