Nanowires created by bacteria offer a cheap, toxin-free future for electronics
Nanowires grown using bacteria have been developed by a team of microbiologists at the University of Massachusetts Amherst, who claim the wires are less resource intensive and cheaper to produce.
The project was started as a way to develop sustainable, green conducting materials for the electronics industry, materials which are typically energy intensive to create and produce harmful toxins during the manufacturing process.
The researchers studied microbial nanowires, protein filaments that bacteria use naturally to make electrical connections with other microbes or minerals.
“Microbial nanowires are a revolutionary electronic material with substantial advantages over man-made materials,” explained Derek Lovley who worked on the project.
“Chemically synthesizing nanowires in the lab requires toxic chemicals, high temperatures and/or expensive metals.
“The energy requirements are enormous. By contrast, natural microbial nanowires can be mass-produced at room temperature from inexpensive renewable feedstocks in bioreactors with much lower energy inputs. And the final product is free of toxic components.”
“Microbial nanowires therefore offer an unprecedented potential for developing novel materials, electronic devices and sensors for diverse applications with a new environmentally friendly technology.”
The team initially focused on working with nanowires created by just one bacterium, Geobacter sulfurreducens.
“Our early studies focused on the one Geobacter because we were just trying to understand why a microbe would make tiny wires,” Lovley said. “Now we are most interested in the nanowires as an electronic material and would like to better understand the full scope of what nature may have to offer for these practical applications.”
When his lab began looking at the protein filaments of other Geobacter species, they were surprised to find a wide range in conductivities.
For example, one species recovered from uranium-contaminated soil produced poorly conductive filaments.
However, another species, Geobacter metallireducens, coincidentally the first Geobacter ever isolated, produced nanowires 5,000 times more conductive than the G. sulfurreducens wires.
In order to capitalise on this, the team took the gene for the protein that assembles microbial nanowires and inserted this into G. sulfurreducens. The result is a genetically modified G. sulfurreducens that expresses the G. metallireducens protein, making nanowires much more conductive than G. sulfurreducens would naturally produce.
“We have found that G. sulfurreducens will express filament genes from many different types of bacteria,” Lovley said. “This makes it simple to produce a diversity of filaments in the same microorganism and to study their properties under similar conditions.
“There is a vast reservoir of filament genes in the microbial world and now we can study the filaments produced from those genes even if the gene comes from a microbe that has never been cultured.”
The researchers attribute G. metallireducens nanowires’ extraordinarily high conductivity to its greater abundance of aromatic amino acids.
Closely packed aromatic rings appear to be a key component of microbial nanowire conductivity and more aromatic rings probably means better connections for electron transfer along the protein filaments.
The high conductivity of the G. metallireducens nanowires suggests that they may be an attractive material for the construction of conductive materials, electronic devices and sensors for medical or environmental applications.