Graphene's long list of achievements is a little longer today, as researchers from Rice University have used the material to make a bacterial bug zapper. A form of the material called laser-induced graphene (LIG) has previously been found to be antibacterial, and now the team has found that those properties can be kicked up a notch by adding a few volts of electricity.
The Rice team, headed up by Professor James Tour, first created LIG in 2014 by using a laser beam to etch patterns into a sheet of polyimide. That churns up the material into a porous graphene foam, which has been found to be effective at preventing microbes from building up on its surface.
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"This form of graphene is extremely resistant to biofilm formation, which has promise for places like water-treatment plants, oil-drilling operations, hospitals and ocean applications like underwater pipes that are sensitive to fouling," says Tour. "The antibacterial qualities when electricity is applied is a great additional benefit."
To further test LIG's bacteria-blasting abilities, the researchers took a sheet of polyimide and used a laser to turn half of the surface into LIG. The material was then placed in a solution full of Pseudomonas aeruginosa bacteria, and a small charge was run through the LIG electrodes. At 1.1 volts, the bacteria, which had been fluorescently tagged so the researchers could see them clearly, were attracted to the LIG anode and moved towards it, like a bug zapper.
At 1.5 volts, the bacteria that came into contact with the LIG were killed within 30 seconds, and when the juice was cranked up to 2.5 volts, it only took one second for them to disappear almost entirely. And because LIG is already a good antifouling material, the dead bugs don't accumulate on its surface.
The top row shows the build-up of bacteria (green) on a plain sheet of polyimide (left), graphite (middle), and laser-induced graphene (right), while the bottom shows the clear split between plain polyimide and electrified LIG (Credit: Arnusch Lab/Ben-Gurion University of the Negev)
Next up, the researchers tested the material as a water-purification technique, leaving these LIG electrodes in a solution of bacteria and partially-treated wastewater. After nine hours at 2.5 volts, the zapper had killed 99.9 percent of the bugs, without forming much of a biofilm on the surface.
"The combination of passive biofouling inhibition and active voltage-induced microbial removal will likely make this a highly sought-after material for inhibiting the growth of troublesome natural fouling that plagues many industries," says Tour.
The scientists aren't sure exactly what's killing the bacteria, but the scenario they suspect sounds pretty gruesome. First the sharp edges of the graphene pierce their cell membranes, then the charge electrocutes them, and any remaining survivors are then quickly poisoned by the hydrogen peroxide that's created in the process.
The research was published in the journal ACS Applied Materials and Interfaces.
The video below shows the bug zapper in action, with the glowing bacteria making their way to the LIG anodes before quickly being destroyed.
Source: Rice University