High-performance antifungal nanohybrid materials composed of melanin-clays

Abstract Melanin is a bio-pigment present in microorganisms, plants, and animals. In humans, melanin has several functions, one of the most important being protection against pathogen microorganisms. With this in mind and considering that clays also have the ability to act against microorganisms, the major aim of this study was to associate natural melanin with clays of different natures (acidic and basic), to form non-toxic and inexpensive hybrid materials presenting enhanced biocidal features. Thus, in this work, a novel hybrid material composed of natural melanin dispersed in an acidic clay (halloysite nanotubes) was successfully synthesized, and its features were compared with those of an anionic clay of the type ZnAl-hydrotalcite, which was also impregnated with melanin in a similar manner. Both clays were tested as antifungal materials against the Trichophyton mentagrophytes fungus. The melanin's mode of integration with the inorganic supports was dependent on the clay type. Melanin in the form of nano-spheres, located between disoriented nano-lamellae, was characterized in the ZnAl-hydrotalcite clay, while its integration with the halloysite clay resulted in disaggregated melanin spherules, located mainly in the openings of the clay nanotubes, or in the form of small plates or films, located in fragmentated zones of the external surface. Both hybrid materials presented high antifungal activity against a very resistant dermatophyte fungus of the species Trichophyton mentagrophytes, with the melanin-halloysite hybrid showing higher efficiency.