Biofunctionalization of zinc oxide nanowires for DNA sensory applications

We report on the biofunctionalization of zinc oxide nanowires for the attachment of DNA target molecules on the nanowire surface. With the organosilane glycidyloxypropyltrimethoxysilane acting as a bifunctional linker, amino-modified capture molecule oligonucleotides have been immobilized on the nanowire surface. The dye-marked DNA molecules were detected via fluorescence microscopy, and our results reveal a successful attachment of DNA capture molecules onto the nanowire surface. The electrical field effect induced by the negatively charged attached DNA molecules should be able to control the electrical properties of the nanowires and gives way to a ZnO nanowire-based biosensing device

The Sheaf-Theoretic Structure Of Non-Locality and Contextuality

We use the mathematical language of sheaf theory to give a unified treatment of non-locality and contextuality, in a setting which generalizes the familiar probability tables used in non-locality theory to arbitrary measurement covers; this includes Kochen-Specker configurations and more. We show that contextuality, and non-locality as a special case, correspond exactly to obstructions to the existence of global sections. We describe a linear algebraic approach to computing these obstructions, which allows a systematic treatment of arguments for non-locality and contextuality. We distinguish a proper hierarchy of strengths of no-go theorems, and show that three leading examples --- due to Bell, Hardy, and Greenberger, Horne and Zeilinger, respectively --- occupy successively higher levels of this hierarchy. A general correspondence is shown between the existence of local hidden-variable realizations using negative probabilities, and no-signalling; this is based on a result showing that the linear subspaces generated by the non-contextual and no-signalling models, over an arbitrary measurement cover, coincide. Maximal non-locality is generalized to maximal contextuality, and characterized in purely qualitative terms, as the non-existence of global sections in the support. A general setting is developed for Kochen-Specker type results, as generic, model-independent proofs of maximal contextuality, and a new combinatorial condition is given, which generalizes the `parity proofs' commonly found in the literature. We also show how our abstract setting can be represented in quantum mechanics. This leads to a strengthening of the usual no-signalling theorem, which shows that quantum mechanics obeys no-signalling for arbitrary families of commuting observables, not just those represented on different factors of a tensor product.Comment: 33 pages. Extensively revised, new results included. Published in New Journal of Physic

Eur. J. Org. Chem.

The octapeptide [134-141] related to the active-site fragment of thioredoxin reductase, in which three residues outside the characteristic Cys-Xaa-Yaa-Cys motif of thiol/disulfide oxidoreductases were replaced by lysines, was head-to-tail- cyclized by using the suitably functionalized (4- aminomethyl)phenylazobenzoic acid (AMPB). The resulting monocyclic and disulfide-bridged bicyclic compounds underwent light-induced cis/trans isomerization in a fully reversible manner, with well-defined conformational transitions as a result of the strong differences in the molecular geometries of the trans and cis-azobenzene units. Correspondingly, the trans and cis forms of the cyclic bis(cysteinyl)-AMPB peptide were characterized by significantly differentiated redox potentials, which were exploited to catalyze the oxidative refolding of reduced RNase A with distinct efficiencies. The experimental results showed that the incorporation of the azobenzene moiety into conformationally restricted bis(cysteinyl) peptide systems provided folding adjuvants that photocontrolled the rates of oxidative protein folding

Space charge-limited current transport in thin films of alkyl-functionalized silicon nanocrystals

We describe the fabrication and electrical characterization of all-silicon electrode devices to study the electronic properties of thin films of silicon nanocrystals (SiNCs). Planar, highly doped Si electrodes with contact separation of 200 nm were fabricated from silicon-on-insulator substrates, by combination of electron beam lithography and reactive ion etching. The gaps between the electrodes of height 110 nm were filled with thin-films of hexyl functionalized SiNCs (diameter 3 nm) from colloidal dispersions, via a pressure-transducing PDMS (polydimethylsiloxane) membrane. This novel approach allowed the formation of homogeneous SiNC films with precise control of their thickness in the range of 15–90 nm, practically without any voids or cracks. The measured conductance of the highly resistive SiNC films at high bias voltages up to 60 V scaled approximately linearly with gap width (5–50 μm) and gap filling height, with little device-to-device variance. We attribute the observed, pronounced hysteretic current–voltage (I–V) characteristics to space-charge-limited current transport, which—after about twenty cycles—eventually blocks the current almost completely. We propose our all-silicon device scheme and gap filling methodology as a platform to investigate charge transport in novel hybrid materials at the nanoscale, in particular in the high resistivity regime

Photocurrent generation of biohybrid systems based on bacterial reaction centers and graphene electrodes

The direct conversion of sunlight into chemical energy via photosynthesis is a unique capability of plants and some bacterial species. Aimed at mimicking this energy conversion process, the combination of inorganic substrates and organic photoactive proteins into an artificial biohybrid system is of a great interest for artificial bio-photovoltaic applications. It also allows to better understand charge transfer processes involved in the photosynthetic chain. In this work, single layer graphene (SLG) and multilayer graphene (MLG) electrodes are used as a platform for the immobilization of reaction centers (RCs) from purple bacteria Rhodobacter sphaeroides, a protein complex responsible for the generation of photo-excited charges. Electrochemical experiments with graphene electrodes and redox molecules reveal fundamental differences in the charge transfer processes for SLG and MLG films. We demonstrate that both graphene-based materials enable the immobilization of RCs without loss of functionality, attested by a photocurrent generation under illumination with IR-light at a wavelength of 870 nm. Furthermore, we report on the dependence of the generated photocurrent on the applied bias voltage, as well as on the presence of charge mediators in the surrounding electrolyte. This work demonstrates that SLG and MLG are a suitable platform for RC immobilization and subsequent photocurrent generation, suggesting a promising potential for graphene-based materials in bio-photovoltaics.The authors acknowledge financial support by the German Research Foundation (DFG) in the framework of the Priority Program 1459 Graphene, DFG CA 1076/3-2, and the European Union under the Graphene Flagship (Contract No. 604391).Peer reviewe

Photomodulation of the redox and folding adjuvant properties of bis(cysteinyl) peptides

The octapeptide [134-141] related to the active-site fragment of thioredoxin reductase, in which three residues outside the characteristic Cys-Xaa-Yaa-Cys motif of thiol/disulfide oxidoreductases were replaced by lysines, was head-to-tail- cyclized by using the suitably functionalized (4- aminomethyl)phenylazobenzoic acid (AMPB). The resulting monocyclic and disulfide-bridged bicyclic compounds underwent light-induced cis/trans isomerization in a fully reversible manner, with well-defined conformational transitions as a result of the strong differences in the molecular geometries of the trans and cis-azobenzene units. Correspondingly, the trans and cis forms of the cyclic bis(cysteinyl)-AMPB peptide were characterized by significantly differentiated redox potentials, which were exploited to catalyze the oxidative refolding of reduced RNase A with distinct efficiencies. The experimental results showed that the incorporation of the azobenzene moiety into conformationally restricted bis(cysteinyl) peptide systems provided folding adjuvants that photocontrolled the rates of oxidative protein folding