Carbon dots (C-dots) represent an emerging class of nontoxic nanoemitters that show excitation wavelength-dependent photoluminescence (PL) with high quantum yield (QY) and minimal photobleaching. The vast majority of studies focus on C-dots that exhibit the strongest PL emissions in the blue/green region of the spectrum, while longer wavelength emissions are ideal for applications such as bioimaging, photothermal and photodynamic therapy and light-emitting diodes. Effective strategies to modulate the PL emission of C-dot-based systems towards the red end of the spectrum rely on extensive conjugation of sp² domains, heteroatom doping, solvatochromism, surface functionalization and passivation. Those approaches are systematically presented in this review, while emphasis is given on important applications of red-emissive suspensions, nanopowders and polymer nanocomposites.

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.