The researchers, led by Christopher Bunker of the Air Force Laboratory in Ohio, have been studying graphene oxide films to see if the material had antimicrobial properties as some previous studies reported. They also looked at how the material affects mammalian cells. Their results indicate that graphene oxide does not inhibit microbial growth but instead actually helps to proliferate both bacterial and mammalian cell growth thanks to the fact that the cells attach to graphene oxide-coated surfaces. "This is a novel observation," said team member Oscar Ruiz.

What is more, if nutrients are included in the culture media, the cells grow even faster and with higher density compared with cultures without graphene oxide. In the case of bacteria, they tend to form thick biofilms packed with bacteria and extracellular polymeric substances, adds Ruiz.

Bioassays
The team obtained its results by developing different bioassays where bacteria were grown on surfaces coated with graphene oxide at different concentrations; on graphene oxide films on their own; and where graphene oxide was added as a suspension to nutrient media. The number of bacteria was then assessed using quantitative real-time PCR (qPCR). "This is a molecular approach that allows us to accurately quantify bacterial DNA over large concentration ranges," said Ruiz. "We also used scanning electron microscopy to further characterize the biofilms formed by the bacteria."

The mammalian cell bioassay was used to characterize how these cells attached to the graphene oxide films and how they grew in the presence and absence of the carbon-based material. Cells were counted and studied by light microscopy in this case.

Tissue engineering and wound healing
"A material that allows faster and more efficient growth of cells would indeed find many applications in the fields of biomedicine and biotechnology," Ruiz told nanotechweb.org. "For example, graphene oxide could be used to develop materials and surfaces that would be used to culture human cells for tissue engineering or to grow structures that could help heal wounds. Other possible applications including deploying the material in bioreactors to increase the production of biopharmaceuticals or to enhance the production of alternative fuels by organisms specially engineered for these purposes.

"We have tried to describe what the real properties of graphene oxide are, to address the conflicting reports in the literature and hopefully use this material ourselves in such applications."

The team, which includes scientists from the University of Dayton Research Institute, Ohio, and Clemson University in South Carolina, described their work in ACS Nano.