With the need for non-antibiotic approaches to microbial pathogenesis being ever present, development of alternatives centred around infection prevention are 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 facile creation of multi-layered 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 tri-layer systems. Both sets of systems were comprised of 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 non-toxic 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 tri-layer systems were made up of Nafion, lysozyme and chitosan, with the other comprising of 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 tri-layer 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.