Functionalization of hydrophobic surfaces with antimicrobial peptides immobilized on a bio-interfactant layer.

The design of functionalized polymer surfaces using bioactive compounds has grown rapidly over the past decade within many industries including biomedical, textile, microelectronics, bioprocessing and food packaging sectors. Polymer surfaces such as polystyrene (PS) must be treated using surface activation processes prior to the attachment of bioactive compounds. In this study, a new peptide immobilization strategy onto hydrocarbonaceus polymer surfaces is presented. A bio-interfactant layer made up of a tailored combination of laccase from trametes versicolor enzyme and maltodextrin is applied to immobilize peptides. Using this strategy, immobilization of the bio-inspired peptide KLWWMIRRWG-bromophenylalanine-3,4-dihydroxyphenylalanine-G and KLWWMIRRWG-bromophenylalanine-G on polystyrene (PS) was achieved. The interacting laccase layers allows to immobilize antimicrobial peptides avoiding the chemical modification of the peptide with a spacer and providing some freedom that facilitates different orientations. These are not strongly dominated by the substrate as it is the case on hydrophobic surfaces; maintaining the antimicrobial activity. Films exhibited depletion efficiency with respect to the growth of Escherichia coli bacteria and did not show cytotoxicity for fibroblast L929. This environmentally friendly antimicrobial surface treatment is both simple and fast, and employs aqueous solutions. Furthermore, the method can be extended to three-dimensional scaffolds as well as rough and patterned substrates.

Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene.

We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene structures. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates.

Polarity-Induced Selective Area Epitaxy of GaN Nanowires.

We present a conceptually novel approach to achieve selective area epitaxy of GaN nanowires. The approach is based on the fact that these nanostructures do not form in plasma-assisted molecular beam epitaxy on structurally and chemically uniform cation-polar substrates. By in situ depositing and nitridating Si on a Ga-polar GaN film, we locally reverse the polarity to induce the selective area epitaxy of N-polar GaN nanowires. We show that the nanowire number density can be controlled over several orders of magnitude by varying the amount of predeposited Si. Using this growth approach, we demonstrate the synthesis of single-crystalline and uncoalesced nanowires with diameters as small as 20 nm. The achievement of nanowire number densities low enough to prevent the shadowing of the nanowire sidewalls from the impinging fluxes paves the way for the realization of homogeneous core-shell heterostructures without the need of using ex situ prepatterned substrates.