While the University of Manchester scientists who discovered graphene, the thinnest yet strongest two-dimensional material yet known, were awarded the 2010 Nobel Prize in Physics, producing it at large scale to use it in new and more efficient computers, medical devices, and other advanced technologies has always been a challenge.
The carbon flake that’s as thin as a single layer of atoms is a revolutionary nanomaterial due to its ability to easily conduct electricity, as well as its extraordinary mechanical strength and flexibility.
Now Anne S. Meyer, an associate professor of biology at the University of Rochester, and her colleagues at Delft University of Technology in the Netherlands, have developed a way to overcome the production issue. The researchers outline their method to produce graphene materials using a novel technique: mixing oxidized graphite with bacteria. Their process is a more cost-efficient, time-saving, and environmentally friendly way of producing graphene materials versus those produced chemically, and could lead to the creation of innovative computer technologies and medical equipment. Meyer’s team has also created graphene materials using “bacterial lithography” that are conductive on one side only, which can lead to the development of new, advanced nanocomposite materials.
“For real applications, you need large amounts,” Meyer says. “Producing these bulk amounts is challenging and typically results in graphene that is thicker and less pure. This is where our work came in.”
In order to produce larger quantities of graphene materials, Meyer and her colleagues started with a vial of graphite. They exfoliated the graphite, shedding the layers of material, to produce graphene oxide (GO), which they then mixed with the bacteria Shewanella. They let the beaker of bacteria and precursor materials sit overnight, during which time the bacteria reduced the GO to a graphene material.
“Graphene oxide is easy to produce, but it is not very conductive due to all of the oxygen groups in it,” Meyer says. “The bacteria remove most of the oxygen groups, which turns it into a conductive material.”
From left to right: A vial of ordinary pencil graphite (Gr); a vial of graphene oxide (GO), produced by exfoliating Gr (shedding the layers of the material) and mixing it with the bacteria Shewanella; a vial of the resulting product: graphene materials (mrGO); and a vial of graphene materials that have been produced chemically (crGO). The graphene materials produced by Anne Meyer’s lab are significantly thinner than the graphene materials produced chemically. (Image Credit: Delft University of Technology/Benjamin Lehner)
While the bacterially produced graphene material created in Meyer’s lab is conductive, it is also thinner and more stable than graphene produced chemically. It can additionally be stored for longer periods of time, making it well suited for a variety of applications, including field-effect transistor (FET) biosensors and conducting ink. FET biosensors are devices that detect biological molecules and could be used to perform, for example, real-time glucose monitoring for diabetics.
“When biological molecules bind to the device, they change the conductance of the surface, sending a signal that the molecule is present,” Meyer says. “To make a good FET biosensor you want a material that is highly conductive but can also be modified to bind to specific molecules.” Graphene oxide that has been reduced is an ideal material because it is lightweight and very conductive, but it typically retains a small number of oxygen groups that can be used to bind to the molecules of interest.
The bacterially produced graphene material could also be the basis for conductive inks, which could, in turn, be used to make faster and more efficient computer keyboards, circuit boards, or small wires such as those used to defrost car windshields. Using conductive inks is an “easier, more economical way to produce electrical circuits, compared to traditional techniques,” Meyer says. Conductive inks could also be used to produce electrical circuits on top of nontraditional materials like fabric or paper.
Source: University of Rochester
