Role of Vacancy Condensation in the Formation of Voids in Rutile TiO2 Nanowires.

Titanium dioxide nanowire (NW) arrays are incorporated in many devices for energy conversion, energy storage, and catalysis. A common approach to fabricate these NWs is based on hydrothermal synthesis strategies. A drawback of this low-temperature method is that the NWs have a high density of defects, such as stacking faults, dislocations, and oxygen vacancies. These defects compromise the performance of devices. Here, we report a postgrowth thermal annealing procedure to remove these lattice defects and propose a mechanism to explain the underlying changes in the structure of the NWs. A detailed transmission electron microscopy study including in situ observation at elevated temperatures reveals a two-stage process. Additional spectroscopic analyses and X-ray diffraction experiments clarify the underlying mechanisms. In an early, low-temperature stage, the as-grown mesocrystalline NW converts to a single crystal by the dehydration of surface-bound OH groups. At temperatures above 500 °C, condensation of oxygen vacancies takes place, which leads to the fabrication of NWs with internal voids. These voids are faceted and covered with Ti3+-rich amorphous TiOx.

Low-copy number protein detection by electrode nanogap-enabled dielectrophoretic trapping for surface-enhanced Raman spectroscopy and electronic measurements.

We report a versatile analysis platform, based on a set of nanogap electrodes, for the manipulation and sensing of biomolecules, as demonstrated here for low-copy number protein detection. An array of Ti nanogap electrode with sub-10 nm gap size function as templates for alternating current dielectrophoresis-based molecular trapping, hot spots for surface-enhanced Raman spectroscopy as well as electronic measurements, and fluorescence imaging. During molecular trapping, recorded Raman spectra, conductance measurements across the nanogaps, and fluorescence imaging show unambiguously the presence and characteristics of the trapped proteins. Our platform opens up a simple way for multifunctional low-concentration heterogeneous sample analysis without the need for target preconcentration.

High-concentration graphene dispersions with minimal stabilizer: a scaffold for enzyme immobilization for glucose oxidation.

Modified acrylate polymers are able to effectively exfoliate and stabilize pristine graphene nanosheets in aqueous media. Starting with pre-exfoliated graphite greatly promotes the exfoliation level. The graphene concentration is significantly increased up to 11 mg mL(-1) by vacuum evaporation of the solvent from the dispersions under ambient temperature. TEM shows that 75 % of the flakes have fewer than five layers with about 18 % of the flakes consisting of monolayers. Importantly, a successive centrifugation and redispersion strategy is developed to enable the formation of dispersions with exceptionally high graphene-to-stabilizer ratio. Characterization by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy shows the flakes to be of high quality with very low levels of defects. These dispersions can act as a scaffold for the immobilization of enzymes applied, for example, in glucose oxidation. The electrochemical current density was significantly enhanced to be approximately six times higher than an electrode in the absence of graphene, thus showing potential applications in enzymatic biofuel cells.

Hollow and yolk-shell iron oxide nanostructures on few-layer graphene in Li-ion batteries.

We report a simple and template-free strategy for the synthesis of hollow and yolk-shell iron oxide (FeOx) nanostructures sandwiched between few-layer graphene (FLG) sheets. The morphology and microstructure of this material are characterized in detail by X-ray diffraction, X-ray absorption near-edge structure, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning and transmission electron microscopy. Its properties are evaluated as negative electrode material for Li-ion batteries and compared with those of solid FeOx/FLG and two commercial iron oxides. In all cases, the content of carbon in the electrode has a great influence on the performance. The use of pristine FLG improves the capacity retention and further enhancement is achieved with the hollow structure. For a low carbon loading of 18 wt. %, the presence of metallic iron in the hollow and yolk-shell FeOx/FLG composite significantly enhances the capacity retention, albeit with a relatively lower initial reversible capacity, retaining above 97% after 120 cycles at 1000 mA g(-1) in the voltage range of 0.1-3.0 V.

Direct loop-mediated isothermal amplification from Plasmodium chabaudi infected blood samples: inability to discriminate genomic and cDNA sequences.

Loop-mediated isothermal amplification (LAMP) has been increasingly used for diagnosis and quantification of pathogens. Since the Bst DNA polymerase used in this assay is highly resistant to PCR inhibitors present in blood, direct analysis of blood samples without DNA or RNA extraction is possible. Indeed, the presence of Plasmodium chabaudi specific nucleic acids was easily detectable using primer sets for P. chabaudi 18S rRNA and the cir 1 mRNA. Despite the fact that primers for cir 1, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and actin II mRNAs were used that spanned an intron, selective amplification of mRNA in the presence of contaminating genomic DNA was not possible. Optimization of the reaction temperature could only improve discrimination when low complexity templates (target sequences cloned in a plasmid vector) were used. Placing different LAMP primers across intron exon boundaries did not prevent amplification in the absence of reverse transcriptase. Probably due to the high A+T content and low number of introns only a very limited number of possible primer sets spanning introns could be identified in the target genes and no reaction conditions could be established that would allow quantification of RNA levels in the presence of DNA directly from blood samples.

Characterization and tissue-specific expression patterns of the Plasmodium chabaudi cir multigene family.

BACKGROUND: Variant antigens expressed on the surface of parasitized red blood cells (pRBCs) are important virulence factors of malaria parasites. Whereas Plasmodium falciparum erythrocyte membrane proteins 1 (PfEMP1) are responsible for sequestration of mature parasites, little is known about putative ligands mediating cytoadherence to host receptors in other Plasmodium species. Candidates include members of the pir superfamily found in the human parasite Plasmodium vivax (vir), in the simian pathogen Plasmodium knowlesi (kir) and in the rodent malarias Plasmodium yoelii (yir), Plasmodium berghei (bir) and Plasmodium chabaudi (cir). The aim of this study was to reveal a potential involvement of cir genes in P. chabaudi sequestration. METHODS: Subfamilies of cir genes were identified by bioinformatic analyses of annotated sequence data in the Plasmodium Genome Database. In order to examine tissue-specific differences in the expression of cir mRNAs, RT-PCR with subfamily-specific primers was used. In total, 432 cDNA clones derived from six different tissues were sequenced to characterize the transcribed cir gene repertoire. To confirm differences in transcription profiles of cir genes, restriction fragment length polymorphism (RFLP) analyses were performed to compare different host tissues and to identify changes during the course of P. chabaudi infections in immunocompetent mice. RESULTS: The phylogenetic analysis of annotated P. chabaudi putative CIR proteins identified two major subfamilies. Comparison of transcribed cir genes from six different tissues revealed significant differences in the frequency clones belonging to individual cir gene subgroups were obtained from different tissues. Further hints of difference in the transcription of cir genes in individual tissues were obtained by RFLP. Whereas only minimal changes in the transcription pattern of cir genes could be detected during the developmental cycle of the parasites, switching to expression of other cir genes during the course of an infection was observed around or after peak parasitemia. CONCLUSIONS: The tissue-specific expression of cir mRNAs found in this study indicates correlation between expression of CIR antigens and distribution of parasites in inner organs. Together with comparable results for other members of the pir superfamily this suggests a role of cir and other pir genes in antigenic variation and sequestration of malaria parasites.