Bacterial attachment to oxygen-functionalized graphenic surfaces

In this work we have investigated the effect of oxygen plasma treatment of graphenic surfaces and the introduction of functional groups on changes in work function, wettability, surface free energy and bacterial adhesion. The plasma parameters were adjusted (generator power: <60 W, exposure time: <20 min) to limit the modifications to the surface without changing the bulk structure. The parent and modified graphenic surfaces were thoroughly characterized by μRaman spectroscopy, thermogravimetry, scanning electron microscopy, contact angle, X-ray photoelectron spectroscopy, work function and microbiological tests. It was found that even the short time of plasma modification results in a significant increase in work function, surface free energy and hydrophilicity. The changes in surface chemistry stimulate also substantial changes in bacterial adhesion. The strong relationship between work function and adhesion of bacteria was observed for all the investigated strains (Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli) whereas the bacterial colonization trend correlates with the bacterial zeta potential. The bacteria-graphenic surface interaction is discussed in terms of total interaction energy. The results point out the work function lowering of the graphenic biomaterial surface as an effective strategy for the infection risk limitation.