Anti-adhesive properties of nanocrystalline diamond films against Escherichia coli bacterium: Influence of surface termination and cultivation medium

Recent interest in industrial and medical usage of carbon nanomaterials arises the need for approved testing protocols for characterizing their interaction with living systems. Nanocrystalline diamond (NCD) films were chosen as a promising material for such investigation due to their unique mechanical properties, chemical stability and biocompatibility. In this study, we examined the anti-adhesive properties of differently terminated NCD films deposited by plasma-enhanced CVD on glass or silicon against Escherichia coli bacterium. We focused on the influence of cultivation medium in this process and compared bacterial adhesion to H-, O- and F-terminated NCD films in complex Luria-Bertani (LB) and mineral (M9) cultivation media that substantially differ in the content of organic molecules and thus in the potential of conditioning film formation. We found the properties of NCD films to be independent of the base substrate, as the amount of biofilm was comparable for both NCD films deposited on glass and on silicon. The anti-adhesive effect was observed only in the mineral medium where hydrogen and fluorine terminated NCD films reduced bacterial adhesion by ca. 50%. In complex medium we did not observe the reduction of bacterial adhesion. These differences are attributed to the passivation of the H- or F-terminated NCD films by organic molecules adsorbed from the complex medium. For O-terminated NCD films, no anti-adhesive effect was observed, regardless of the cultivation medium. Our results show that the growth of Escherichia coli in mineral cultivation medium can be affected by the diamond atomic termination.