Experiments using laser-induced graphene have shown it to be an effective solution for fighting bacteria, and may be of particular interest to the oil and gas industry
Another week, another newfound application for graphene: in this case, the material in question is in fact laser-induced graphene (LIG), a material similar to the ubiquitous single-layer carbon sheet but which also possesses sponge-like qualities.
LIG was first developed in 2014 by Rice University chemist James Tour, arguably the father of modern nanotechnology. Experiments in his lab successfully burned part of the way through a sheet of polyimide with a laser, turning the surface into a lattice of interconnected graphene sheets. The material has even been touted as a possible energy storage solution as a potential replacement for supercapacitors, and even batteries. Researchers have since suggested applications in wearable electronics and fuel cells, as well as for superhydrophobic or superhydrophilic surfaces. Most recently, however, LIG has been used as part of an effective anti-bacterial treatment method, having been shown to protect surfaces from biofouling in water. According to a paper published by scientists at Rice University, Texas and Ben-Gurion University of the Negev (BGU), when electrified, LIG can even be used to “zap” bacteria.
Bugging out The antibacterial properties of graphene have long been discussed; however, this research goes some way towards proving and quantifying to what extent this occurs. The team has also proved that the effect is magnified dramatically when a voltage is applied across the material.
The paper, led by BGU postdoc fellow Swatantra Singh and Rice grad student Yilun Liare, and co-authored by BGU’s Senior Lecturer Avraham Be’er and Emeritus Professor Yoram Oren, describes applying varying voltages between 1.1-2.5V, during which the LIG electrodes biocidal effects were “greatly enhanced.” As Rice notes in its statement, it transforms LIG into “the bacterial equivalent of a backyard bug zapper.”
In an experiment, fluorescently tagged pseudomonas aeruginosa bacteria were deposited in a solution with LIG electrodes above 1.1V. Viewing the process under a microscope, the team observed the bacteria being drawn toward the anode, and above 1.5V, the cells began to disappear, vanishing completely within 30 seconds. At 2.5V, bacteria disappeared almost completely from the surface after one second.
Rice then partnered with Professor Christopher Arnusch, a lecturer at the BGU Zuckerberg Institute for Water Research and who specialises in water purification. Arnusch lab-tested LIG electrodes in a bacteria-laden solution with 10% secondary treated wastewater and found that after nine hours at 2.5V, 99.9% of bacteria were killed and the electrodes strongly resisted biofilm formation.
The exact cause of the bacterial removal is unknown, but the team suspects a combination of factors. Primarily, the sharp edges of the graphene surface are thought to pierce and destroy the bacterial membranes, but in addition to the electrical voltage itself, the researchers also observed localised electrochemical generation of hydrogen peroxide – an effective biocide. In their paper abstract, the authors note: “The bacterial killing mechanism depended strongly on the physical and electrical contact of the bacterial cells to the surfaces.”
Moreover, LIG’s anti-fouling properties also prevent dead bacteria from accumulating on the surface, Tour said. “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,” Tour said, specifically referencing “places like water-treatment plants, oil-drilling operations, hospitals and ocean applications like underwater pipes that are sensitive to fouling.”
In emailed comments to InnovOil, Tour confirmed that commercial deployment of the LIG system could be done via a polymer film applied physically within the areas to be protected. Moreover, he said, LIG is not an overly expensive material; it can be produced with commercial plastics and electricity, all in air and at room temperature. All this could make it a very viable solution for the prevention of biofilm growth in the oilfield – bacteria beware.