Using graphene to fight bacteria

Graphene is a new wonder material first characterised in the last decade - work recognised with the 2010 Nobel Prize in physics. This single-atom-thin sheet material holds promise in future electronics, battery and manufacturing technologies.

"We want to make materials that will help patients and medical professionals," said Valentina Palmieri a biotechnologist at the Università Cattolica del Sacro Cuore in Rome.

Graphene oxide, a form of graphene with molecular oxygen incorporated into it, protects against infection by destroying bacteria before it gets inside the body. The graphene oxide wraps around the bacteria, puncturing its membrane.

A broken membrane prevents the bacteria from growing and often kills it. "The bacteria lose their complex structure and die," Palmieri added. "And since graphene is just carbon - a building block of life - its cytotoxicity against human cells is much lower compared to any drug-based antimicrobial therapy."

Researchers decided to use graphene oxide because it is very stable in a water solution, making it safe to interact with human cells. Graphene specifically attacks bacterial cells, while sparing human cells, and the mechanism behind this specificity is still unclear, Palmieri said.

Current theories include that the material interacts more favorably with the bacterial cell wall or that mammalian cells have evolved multiple repair mechanisms to survive the chemical oxidation damage that graphene induces.

Graphene is also more eco-friendly. Traditional methods of preventing infection include antibiotic therapy and tools coated with silver -- both of which are toxic to the environment, Palmieri said.

The compound is most effective when paired with salt. Too little salt and the graphene oxide won't wrap around the bacteria. Too much salt and the graphene aggregates, failing to puncture the bacteria's membrane.

To destroy both Gram positive and Gram negative bacteria, two major categories of bacteria to which many hospital-acquired pathogens belong, a 300 nanometer sheet of graphene oxide solution must be mixed with low molarity (<10 mM) Calcium chloride.

Palmieri and her team also created new protocol methods for testing the effectiveness of the graphene oxide and salt mixture.

Researchers normally use a spectrophotometer to test whether the solution has killed all the bacteria. This method didn't account for any bacteria that may have fallen to the bottom of the solution. Instead, Palmieri uses two different wavelengths of light - one that is sensitive to absorbing and one that is sensitive to scattering - to check for bacteria.

The next step is to test graphene oxide's effectiveness against fungi. Fungi can also cause significant problems if they infect an open wound. Up until this point, though, fungi cells are too big for graphene oxide to wrap all the way around them. Palmieri says she wants to alter the salt content inside the saline solution to see if she can solve this issue.