Circumventing the ammonia-related growth suppression for obtaining regular GaN nanowires by HVPE.

Selective area growth by hydride vapor phase epitaxy of GaN nanostructures with different shapes was investigated versus the deposition conditions including temperature and ammonia flux. Growth experiments were carried out on templates of GaN on sapphire masked with SiNx. We discuss two occurrences related to axial and radial growth of GaN nanowires. A growth suppression phenomenon was observed under certain conditions, which was circumvented by applying the cyclic growth mode. A theoretical model involving inhibiting species was developed to understand the growth suppression phenomenon on the masked substrates. Various morphologies of GaN nanocrystals were obtained by controlling the competition between the growth and blocking mechanisms as a function of the temperature and vapor phase composition. The optimal growth conditions were revealed for obtaining regular arrays of ∼5µm long GaN nanowires.

SE(R)RS devices fabricated by a laser electrodispersion method.

A novel laser electrodispersion (LE) technique was employed to deposit gold nanoparticles onto Si and SiO(x) surfaces. The LE technique combines laser ablation with cascade fission of liquid metal micro-drops, which results in the formation of nanoparticles upon rapid cooling. The shape and the size distribution of the Au nanoparticles prepared by LE depend on the nature of the support. Gold nanoparticles were also deposited in the channels of microreactors fabricated by wet etching of Si and used as SE(R)RS sensors. The influence of the nanoparticle surface density as well as of the nature of the substrate on the Raman response was studied. At an appropriate surface density of the deposited nanoparticles a significant enhancement of Raman signal was observed showing the possibility to create efficient SERS substrates. Application of microfluidic devices in surface enhanced Raman spectroscopy (SERS) in continuous-flow mode with sensor regeneration is described.

Single protein molecule mapping with magnetic atomic force microscopy.

Understanding the structural organization and distribution of proteins in biological cells is of fundamental importance in biomedical research. The use of conventional fluorescent microscopy for this purpose is limited due to its relatively low spatial resolution compared to the size of a single protein molecule. Atomic force microscopy (AFM), on the other hand, allows one to achieve single-protein resolution by scanning the cell surface using a specialized ligand-coated AFM tip. However, because this method relies on short-range interactions, it is limited to the detection of binding sites that are directly accessible to the AFM tip. We developed a method based on magnetic (long-range) interactions and applied it to investigate the structural organization and distribution of endothelin receptors on the surface of smooth muscle cells. Endothelin receptors were labeled with 50-nm superparamagnetic microbeads and then imaged with magnetic AFM. Considering its high spatial resolution and ability to "see" magnetically labeled proteins at a distance of up to 150 nm, this approach may become an important tool for investigating the dynamics of individual proteins both on the cell membrane and in the submembrane space.

Correction: Functional modulation and directed assembly of an enzyme through designed non-natural post-translation modification.

[This corrects the article DOI: 10.1039/C4SC03900A.].

Apparent two-dimensional behavior of TiO2 nanotubes revealed by light absorption and luminescence.

Optical absorption and photoluminescence (PL) properties of colloidal TiO(2) nanotubes, produced by the alkali hydrothermal method, were studied at room temperature in the range 300-700 nm. Nanotubes having an internal diameter in the range 2.5-5 nm have very similar optical properties, in contrast to the expected behavior for quasi-1-D systems. This is explained by the complete thermal smearing of all 1-D effects, due to the large effective mass of charge carriers in TiO(2), resulting in an apparent 2-D behavior of TiO(2) nanotubes.

Functional modulation and directed assembly of an enzyme through designed non-natural post-translation modification.

Post-translational modification (PTM) modulates and supplements protein functionality. In nature this high precision event requires specific motifs and/or associated modification machinery. To overcome the inherent complexity that hinders PTM's wider use, we have utilized a non-native biocompatible Click chemistry approach to site-specifically modify TEM ß-lactamase that adds new functionality. In silico modelling was used to design TEM ß-lactamase variants with the non-natural amino acid p-azido-l-phenylalanine (azF) placed at functionally strategic positions permitting residue-specific modification with alkyne adducts by exploiting strain-promoted azide-alkyne cycloaddition. Three designs were implemented so that the modification would: (i) inhibit TEM activity (Y105azF); (ii) restore activity compromised by the initial mutation (P174azF); (iii) facilitate assembly on pristine graphene (W165azF). A dibenzylcyclooctyne (DBCO) with amine functionality was enough to modulate enzymatic activity. Modification of TEMW165azF with a DBCO-pyrene adduct had little effect on activity despite the modification site being close to a key catalytic residue but allowed directed assembly of the enzyme on graphene, potentially facilitating the construction of protein-gated carbon transistor systems.