Analysis of Bacterial Adhesion with Graphene Oxide-Modified PES Ultrafiltration Membranes

Abstract

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. AFM-based single-cell force spectroscopy (SCFS) was used to show that coatings comprising GO nanosheets bonded to a hydrophilic polymer brush, mitigate adhesion of Pseudomonas fluorescens cells, while preserving GO’s intrinsic biocidal activity. This work demonstrated the simultaneous biocidal and 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. The chemistry and interfacial properties of the unmodified PES, PAA-modified (PES-PAA), and GO-modified PES (PES-GO) substrates were demonstrated 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, it was shown 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 were skewed towards weaker values compared to the PES control (F ̅Peak = -0.18 nN). The results show that weaker adhesion on PES-GO was 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 allowed by the brush-like GO-PAA interface.