The study focuses on the development of a new family of layer-by-layer coatings comprising Nafion, lysozyme and chitosan to address challenges related to microbial contamination. Circular dichroism was employed to gain insights on the interactions of the building blocks at the molecular level. Quartz crystal microbalance tests were used to monitor in real time the build-up of multilayer coatings, while atomic force microscopy, contact angle and surface zeta potential measurements were performed to assess the surface characteristics of the multilayer assemblies. Remarkably, the nanocoated surfaces show almost 100% reduction in the population of both Escherichia coli and Staphylococcus aureus. The study suggests that Nafion based synergistic platforms can offer an effective line of defence against bacteria, facilitating antimicrobial mechanisms that go beyond the concept of exclusion zone.

We present a simple strategy to generate a family of carbon dots/iron oxide nanoparticles (C/Fe-NPs) that relies on the thermal decomposition of iron (III) acetylacetonate in the presence of a highly fluorescent carbon-rich precursor (derived via thermal treatment of ethanolamine and citric acid at 180 °C), while polyethylene glycol serves as the passivation agent. By varying the molar ratio of the reactants, a series of C/Fe-NPs have been synthesized with tuneable elemental composition in terms of C, H, O, N and Fe. The quantum yield is enhanced from 6 to 9% as the carbon content increases from 27 to 36 wt%, while the room temperature saturation magnetization is improved from 4.1 to 17.7 emu/g as the iron content is enriched from 17 to 31 wt%. In addition, the C/Fe-NPs show excellent antimicrobial properties, minimal cytotoxicity and demonstrate promising bioimaging capabilities, thus showing great potential for the development of advanced diagnostic tools.

Nafion and amine-terminated graphene oxide (GO–NH ₂ ) coatings inhibit bacterial growth by 99% and this performance is maintained upon thermal annealing.

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.

This paper presents a simple, post-synthesis treatment of carbon dots (C-dots) that relies on the oxidizing activity of sodium hypochlorite to induce surface oxidation, etching and pronounced structural rearrangements. The thus treated C-dots (ox-C-dots) exhibit up to six-fold enhancement in quantum yield compared to non-oxidised analogues, while maintaining low levels of cytotoxicity against HeLa and U87 cell lines. In addition, we demonstrate that a range of polymeric materials (polyurethane sponge, polyvinylidene fluoride membrane, polyester fabric) impregnated with ox-C-dots show advanced antifungal properties against Talaromyces pinophilus, while their untreated counterparts fail to do so.

Carbogenic nanoparticles (also known as C-dots) constitute a new class of carbon-based materials, which are easily synthesized via thermal treatments of carbon-rich precursors. These spherical nano-emitters are composed of an amorphous core with an approximate size of below 10 nm and exhibit exquisite biocompatibility, simplicity of surface modification, excellent chemical stability and broad excitation spectra. Their exceptional photoluminescent properties are related to the dual emissive mode with the excitation-wavelength independent or dependent emission, attributed to the presence of organic fluorophores or carbogenic cores, respectively. To date, several nanomaterials have been developed to measure the intercellular pH, including fluorescent proteins, organic dyes and quantum dots. Among them, C-dots are characterized by resistance to photobleaching, good permeability and lack of toxic metal components in their structure. Moreover, these nanoemitters demonstrate excellent analytical performance in detecting heavy metals, drugs, biological molecules, poisonous reactants or explosives and thus can be applied as highly selective optical nanoprobes. In summary, our results demonstrate the potential to utilize biocompatible carbogenic nanotracers for an early-stage disease diagnosis as well as highlight their remarkable antimicrobial activity against Escherichia coli and Staphylococcus aureus.