Will your future computer be made with bacteria?

In order to create new computers, medical devices and other more efficient advanced technologies, researchers turned to nanomaterials: materials handled on the scale of atoms or molecules with unique properties.

Graphene – a film of carbon as thin as an atom – is a revolutionary nanomaterial because of its ability to easily conduct electricity, as well as its extraordinary mechanical strength and flexibility. However, one of the major obstacles to its adoption for everyday applications is to produce graphene on a large scale, while maintaining its astonishing properties.

In an article published in the journal ChemOpenAnne S. Meyer, an associate professor of biology at the University of Rochester, and her colleagues at the Delft University of Technology in the Netherlands, describe a way to overcome this obstacle. The researchers describe their method for producing graphene materials using a new technique: mixing oxidized graphite with bacteria. Their method represents a more economical, faster and more environmentally friendly way of producing graphene materials than chemically produced ones, and could lead to the creation of innovative computer technologies and medical equipment.

Graphene is extracted from graphite, the material found in an ordinary pencil. At exactly one atom of thickness, graphene is the thinnest – and most resistant – two-dimensional material known to researchers. Scientists from the University of Manchester in the United Kingdom received the 2010 Nobel Prize in Physics for their discovery of graphene; However, their method of using duct tape to make graphene only produced small amounts of the material.

"For real applications, you need large quantities," says Meyer. "Producing these quantities in bulk is difficult and usually gives thicker and less pure graphene – this is where our work has been implemented."

In order to produce larger quantities of graphene, Meyer and his colleagues started with a flask of graphite. They exfoliated the graphite – eliminating the layers of material – to produce graphene oxide (GO), which they then mixed with the Shewanella bacteria. They let the beaker of bacteria and the precursor materials sit overnight, during which time the bacteria reduce the GO to graphene.

"Graphene oxide is easy to produce, but it is not very conductive because of all the oxygen groups it contains," says Meyer. "Bacteria eliminate most oxygen groups, making it a conductive material."

Although graphene produced by bacteria and created by Meyer's laboratory is conductive, it is also thinner and more stable than chemically produced graphene. In addition, it can be stored for longer periods of time, making it well suited for a variety of applications, including field effect transistor (FET) biosensors and conductive ink. FET biosensors are devices that detect biological molecules and could be used to perform, for example, real-time blood glucose monitoring for diabetics.

"When biological molecules bind to the device, they change the surface conductance, sending a signal that the molecule is present," says Meyer. "To make a good FET biosensor, you need a highly conductive material that can also be modified to bind specific molecules." Reduced graphene oxide is an ideal material because it is lightweight and highly conductive, but it generally retains a small number of oxygen groups that can be used to bind the molecules of interest.

Graphene produced by bacteria could also be used as a basis for conductive inks, which could in turn be used to make computer keyboards, printed circuit boards, or faster and more efficient wire, such as those used to defrost the windshields of cars. The use of conductive inks is a "simpler and more economical way to produce electrical circuits, compared to traditional techniques," explains Meyer. Conductive inks could also be used to produce electrical circuits from non-traditional materials such as fabric or paper.

"Our graphene material produced by bacteria will greatly enhance the adaptability to product development," Meyer said. "We have even been able to develop a technique of" bacterial lithography "to create conductive graphene materials on one side, which can lead to the development of new advanced nanocomposite materials."