Nafion-Based Layer-by-Layer Coatings with Antimicrobial Activity

Abstract

With the need for non-antibiotic approaches to microbial pathogenesis being ever present, the development of alternatives centred around infection prevention is of deep importance. Antimicrobial surface coatings offer a promising approach, as they can possess multiple favourable qualities such as low toxicity, longevity, and the capacity for re-coating. Of the possible coating methods, layer-by-layer (LbL) deposition provides a particularly useful approach, allowing for the facile creation of multilayered coatings on pre-existing surfaces. For these LbL coatings, Nafion, a synthetic polymer with excellent mechanical properties, was used as a stable foundation for two model trilayer systems. Both sets of systems comprised Nafion layered alongside compounds with well-established antimicrobial activity: lysozyme, chitosan, and carbon dots (CDots). In addition to their antimicrobial properties, lysozyme and chitosan are both nontoxic and biocompatible, making them ideal for biomedical applications. Similarly, CDots have low toxicity but also possess fluorescent properties, opening up the potential for the assessment of coating integrity, making these coatings suitable for high-wear surfaces. As such, the two trilayer systems were made of, respectively, Nafion, lysozyme, and chitosan; and Nafion, lysozyme, and CDots. When assessed against the representative Gram-negative and Gram-positive species Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, both trilayer systems showed excellent antimicrobial activity, producing up to 3 log reductions in colony-forming units compared with a control. The activity of both sets of systems, alongside the similar activity between systems, showed both good synergy between and interchangeability of layer components, opening up the possibility for further tailoring in future.