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Accurate assessment of the antibacterial activity of graphene requires consideration of both the graphene fabrication method and, for supported films, the properties of the substrate.Large-area graphene films produced by chemical vapor deposition were grown directly on copper substrates or transferred on a gold substrate and their effect on the viability and proliferation of the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli were assessed. The viability and the proliferation of both bacterial species were not affected when they were grown on a graphene film entirely covering the gold substrate, indicating that conductivity plays no role on bacterial viability and graphene has no antibacterial activity against S. aureus and E. coli. On the other hand, antibacterial activity * Corresponding author : Email address : louis.dellieu@unamur.be (L. Dellieu) FAX : +32 81 72 44 64 2 was observed when graphene coated the copper substrates, resulting from the release of bactericidal cupric ions in inverse proportion to the graphene surface coverage.

Nanostructures are commonly used for developing superhydrophobic surfaces. However, available wetting theoretical models ignore the effect of vacuum photon-mode alteration on van der Waals forces and thus on hydrophobicity. Using first-principles calculations, we show that superhydrophibicity of nanostructured surfaces is dramatically enhanced by vacuum photon-mode tuning. As a case study, wetting contact angles of a water droplet above a polyethylene nanostructured surface are obtained from the interaction potential energy calculated as a function of the droplet-surface separation distance. This new approach could pave the way for the design of novel superhydrophobic coatings.

Natural nanostructures rarely come with a single biological function to fulfil. Moreover, from a bio-inspiration perspective, it sounds attractive to develop multifunctional coatings, devices or sensors. Suppression of light reflection from body parts, such as the wings of insects, is useful for hiding from predators. The transparent parts of the wings of Cacostatia ossa (moth) inherit their antireflective property from non-close-packed nano-scale nipple arrays on both sides of the wings. Through modelling and optical simulations, we show that effective medium approaches, commonly used to characterize antireflection, slightly overestimate the reflectance with respect to detailed Rigorous Coupled Wave Analysis calculation. Coloration due to light interference in nanostructure, on the other hand, sometimes comes with an additional, unexpected and maybe non-biologically significant function: hygrochromism, i.e. change of color with humidity. The male Hoplia coerulea (beetle), for instance, exhibits iridescent blue-violet color which turns to emerald green when the elytron is put in contact with water. Impregnation experiments with various liquids revealed intriguing color change dynamics which could be related to the wetting properties of porous chitinous cuticle. Super-hydrophobicity is another function of biological significance, which helps, for instance, insects to keep dry in humid environments. Through morphological, optical and contact angle measurements, we show the existence of entangled levels of functionality on the wings of Cicada orni, namely a superhydrophobic stage at the upper part of the nipple array corrugated surface and an antireflective stage and the lower part.

The bridge between quantum vacuum photon modes and properties of patterned surfaces is currently being established on solid theoretical grounds. Based on these foundations, the manipulation of quantum vacuum photon modes in a nanostructured cavity is theoretically shown to be able to turn the Lifshitz-van der Waals forces from attractive to repulsive regime. Since this concept relies on surface nanopatterning instead of chemical composition changes, it drastically relaxes the usual conditions for achieving repulsive Lifshitz-van der Waals forces. As a case study, the potential interaction energy between a nanopatterned polyethylene slab and a flat polyethylene slab with water as intervening medium is calculated. Extremely small corrugations heights (less than ten nanometers) are shown to be able to turn the Lifshitz-van der Waals force from attractive to repulsive, the interaction strength being controlled by the corrugation height. This new approach could lead to various applications in surface science. 1 These authors have contributed equally to this work.