Insight into the mechanisms underlying bacterial adhesion is critical to the formulation of membrane biofouling control strategies. Using AFM-based single-cell force spectroscopy, we investigated the interaction between Pseudomonas fluorescens, a biofilm-forming bacterium, and polysulfone (PSF) ultrafiltration (UF) membranes to unravel the mechanisms underlying early stage membrane biofouling. We show that hydrophilic polydopamine (PDA) coatings decrease bacterial adhesion forces at short bacterium-membrane contact times. Further, we find that adhesion forces are weakened by the presence of natural organic matter (NOM) conditioning films, owing to the hydrophilicity of NOM. Investigation of the effect of adhesion contact time revealed that PDA coatings are less effective at preventing bioadhesion when the contact time is prolonged to 2-5 s, or when the membranes are exposed to bacterial suspensions under stirring. These results therefore challenge the notion that simple hydrophilic surface coatings are effective as a biofouling control strategy. Finally, we present evidence that adhesion to the UF membrane surface is mediated by cell-surface macromolecules (likely to be outer membrane proteins and pili) which, upon contacting the membrane, undergo surface-induced unfolding.

The potential of graphene oxide (GO) in environmental applications, such as the development of antimicrobial materials and low-fouling membranes, has thus far been hindered by an incomplete understanding of bioadhesion mechanisms on GO interfaces. Using atomic force microscopy (AFM)-based single-cell force spectroscopy, we investigate the adhesion of single Pseudomonas fluorescens cells on GO-functionalized interfaces possessing distinct morphologies. Specifically, we investigate Si-GO surfaces, in which Langmuir−Blodgett GO films are transferred to Si wafers by dip-coating, forming an immobilized layer of horizontally arranged GO nanosheets, and PLL-GO surfaces, where GO nanosheets, edge-tethered to poly-L-lysine, form an interface characterized by morphological and conformational disorder. We observe strong adhesion forces on both Si-GO and PLL-GO surfaces; analysis of the pull-off forces in terms of the worm-like chain model reveals that adhesion is driven by hydrophobic interactions between proteinaceous adhesins on P. fluorescens and graphenic basal planes. We further show that adhesion forces are significantly stronger on Si-GO surfaces that facilitate interactions with graphenic planes, compared to PLL-GO surfaces, which show weaker adhesion due to steric and electrostatic repulsion. These results therefore demonstrate that the spatial orientation and conformational disorder of GO nanosheets are key factors governing the interfacial properties of graphene nanomaterials.

No abstract

Graphene oxide (GO) is a biocidal nanomaterial, but is it also anti-adhesive? Here we show that GO-based coatings exhibiting low bacterial adhesion properties can be formed by edge-tethering GO nanosheets to hydrophilic polymer brushes.