Do graphene oxide nanostructured coatings mitigate bacterial adhesion?

Given its potent biocidal properties, graphene oxide (GO) holds promise as a building block of anti-microbial surfaces, with numerous potential environmental applications. Nonetheless, the extent to which GO-based coatings decrease bacterial adhesion propensity, a necessary requirement of low-fouling surfaces, remains unclear. Here we use AFM-based single-cell force spectroscopy (SCFS) to show that coatings comprising GO nanosheets bonded to a hydrophilic polymer brush mitigate adhesion of Pseudomonas fluorescens cells. We demonstrate low-adhesion GO coatings by grafting poly(acrylic acid) (PAA) to polyethersulfone (PES) substrates via self-initiated UV polymerization, followed by edge-tethering of GO to the PAA chains through amine coupling. We characterize the chemistry and interfacial properties of the unmodified PES, PAA-modified (PES–PAA), and GO-modified (PES–GO) substrates using ATR-FTIR, Raman spectroscopy, contact angle goniometry, and AFM to confirm the presence of PAA and covalently bonded GO on the substrates. Using SCFS we show that peak adhesion force distributions for PES–PAA (with mean adhesion force [F with combining macron]Peak = −0.13 nN) and PES–GO ([F with combining macron]Peak = −0.11 nN) substrates are skewed towards weaker values compared to the PES control ([F with combining macron]Peak = −0.18 nN). Our results show that weaker adhesion on PES–GO is due to a higher incidence of non-adhesive (repulsive) forces (45.9% compared to 22.2% over PES–PAA and 32.3% over PES), which result from steric repulsion afforded by the brush-like GO–PAA interface. Lastly, we show that attachment to the various substrates is due to interactions of proteinaceous adhesins whose force response is well described by the worm-like chain model of polymer elasticity.