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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 Peak = -0.13 nN) and PES-GO (F Peak = -0.11 nN) substrates are skewed towards weaker values compared to the PES control (F 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.
Bibliographical noteFunding Information:
This work was supported by the Environment and Natural Resources Trust Fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources. Portions of this work were carried out in the Characterization Facility at UMN, supported by NSF through award DMR-1420013, and at the Minnesota Nano Center, which receives partial support from NSF through the National NanoCoordinated Infrastructure Network (NNCI) (Award Number ECCS-1542202). SRVC is grateful to 3M Co. for a Non-Tenured Faculty Award.
© 2019 The Royal Society of Chemistry.