The aim of this study is to prove that resistive heating enables the synthesis of metal/metal oxide composites in the form of core-shell structures. The thickness and morphology of the oxide layer ...depends strongly on the nature of the metal, but the influences of parameters such as the time and current profiles and the presence of an external field have also been investigated. The systems chosen for the present study are Zn/ZnO, Ti/TiO
, and Ni/NiO. The characterization of the samples was performed using techniques based on scanning electron microscopy (SEM). The thicknesses of the oxide layers varied from 10 μm (Zn/ZnO) to 50 μm (Ni/NiO). In the case of Zn- and Ti-based composites, the growth of nanostructures on the oxide layer was observed. Micro- and nanoneedles formed on the ZnO layer while prism-like structures appeared on the TiO
. In the case of the NiO layer, micro- and nanocrystals were observed. Applying an external electric field seemed to align the ZnO needles, whereas its effect on TiO
and NiO was less appreciable, principally affecting the shape of their grain boundaries. The chemical compositions were analysed using X-ray spectroscopy (EDX), which confirmed the existence of an oxide layer. Structural information was obtained by means of X-ray diffraction (XRD) and was later checked using Raman spectroscopy. The oxide layers seemed to be crystalline and, although some non-stoichiometric phases appeared, the stoichiometric phases were predominant; these were wurtzite, rutile, and cubic for Zn, Ti, and Ni oxides, respectively. The photoluminescence technique was used to study the distribution of defects on the shell, and mainly visible bands (2-2.5 eV), attributed to oxygen vacancies, were present. The near-band edges of ZnO and TiO
were also observed around 3.2-3.3 eV.
ZnO nano- and microstructures doped with K were grown by the Vapor–Solid method. Wires and needles are the main morphology observed, although some structures in the form of ribbons and triangular ...plates were also obtained. Besides these, ball-shaped structures which grow around a central wire were also detected. Raman and cathodoluminescence investigations suggest that variations in morphology, crystalline quality and luminescence emissions are related to the different lattice positions that K occupies depending on its concentration in the structures. When the amount is low, K ions mainly incorporate as interstitials (Ki), whereas K occupies substitutional positions of Zn (KZn) when the amount of K is increased. Electron Backscattered Diffraction shows that ribbons and triangular plates are oriented in the (0001) direction, which indicates that the growth of this type of morphologies is related to distortions introduced by the Ki since this position favors the growth in the (0001) plane. In the case of the ball-shaped structures, the compositional analysis and Raman spectra show that they consist of K2SO4. Finally, the capability of the elongated structures to act as waveguides and optical resonators was investigated. Due to the size of the K ion, practically double that of the Zn, and the different positions it can adopt within the ZnO lattice (Ki or KZn), high distortions are introduced that compromise the resonators performance. Despite this, quality factor (Q) and fineness (F) show acceptable values (80 and 10 at 544 nm, respectively), although smaller than those reported for doping with smaller size alkali, such as Li.
Low Sensitivity of BinaxNOW RSV in Infants Zuurbier, Roy P; Bont, Louis J; Langedijk, Annefleur C ...
The Journal of infectious diseases,
10/2020, Letnik:
222, Številka:
Supplement_7
Journal Article
Recenzirano
Odprti dostop
Abstract
Background
Respiratory syncytial virus (RSV) is a major cause of hospitalization in infants. Early detection of RSV can optimize clinical management and minimize use of antibiotics. BinaxNOW ...RSV (BN) is a rapid antigen detection test that is widely used. We aimed to validate the sensitivity of BN in hospitalized and nonhospitalized infants against the gold standard of molecular diagnosis.
Methods
We evaluated the performance of BN in infants with acute respiratory tract infections with different degrees of disease severity. Diagnostic accuracy of BN test results were compared with molecular diagnosis as reference standard.
Results
One hundred sixty-two respiratory samples from 148 children from October 2017 to February 2019 were studied. Sixty-six (40.7%) samples tested positive for RSV (30 hospitalizations, 31 medically attended episodes not requiring hospitalization, and 5 nonmedically attended episodes). Five of these samples tested positive with BN, leading to an overall sensitivity of BN of 7.6% (95% confidence interval CI, 3.3%–16.5%) and a specificity of 100% (95% CI, 96.2%–100%). Sensitivity was low in all subgroups.
Conclusions
We found a low sensitivity of BN for point-of-care detection of RSV infection. BinaxNOW RSV should be used and interpreted with caution.
ZnO nano- and microstructures co-doped with Eu and Li with different nominal concentrations of Li were grown using a solid vapor method. Different morphologies were obtained depending on the initial ...Li content in the precursors, varying from hexagonal rods which grow on the pellet when no Li is added to ribbons to sword-like structures growing onto the alumina boat as the Li amount increases. The changes in the energy of the crystallographic planes leading to variations in the growth directions were responsible for these morphological differences, as Electron Backscattered Diffraction analysis shows. The crystalline quality of the structures was investigated by X-ray diffraction and Raman spectroscopy, showing that all the structures grow in the ZnO wurtzite phase. The luminescence properties were also studied by means of both Cathodoluminescence (CL) and Photoluminescence (PL). Although the typical ZnO luminescence bands centered at 3.2 and 2.4 eV could be observed in all cases, variations in their relative intensity and small shifts in the peak position were found in the different samples. Furthermore, emissions related to intrashell transitions of Eu3+ ion were clearly visible. The good characteristics of the luminescent emissions and the high refraction index open the door to the fabrication of optical resonant cavities that allow the integration in optoelectronic devices. To study the optical cavity behavior of the grown structures, µ-PL investigations were performed. We demonstrated that the structures not only act as waveguides but also that Fabry–Perot optical resonant modes are established inside. Quality factors around 1000 in the UV region were obtained, which indicates the possibility of using these structures in photonics applications.
In this work, ZnSe and ZnTe micro‐ and nanostructures are grown by the vapor‐solid method. Thermal treatments are performed in an inert atmosphere (Ar) to avoid the oxidation of the samples, at 900 ...°C for 24 h. The structures obtained are investigated by SEM and HRTEM to assess morphology and microstructure. The optical properties are investigated by cathodoluminenscence technique. The bandgaps of these compounds are 2.8 eV for ZnSe and 2.4 eV for ZnTe, however, the luminescence study is extended toward red and near infrared regions to investigate the defect levels. The influence of the size and morphology of the structures on the luminescence properties are studied.
Vapor‐solid method is used to grow micro‐ and nanostructures of ZnSe and ZnTe. The morphology of the structures is studied using SEM and TEM. Cathodoluminescence measurements are performed to study the optical properties in the visible and near‐infrared range.
Human respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection in young children globally, but little is known about within-host RSV diversity. Here, we characterised ...within-host RSV populations using deep-sequencing data from 319 nasopharyngeal swabs collected during 2017-2020. RSV-B had lower consensus diversity than RSV-A at the population level, while exhibiting greater within-host diversity. Two RSV-B consensus sequences had an amino acid alteration (K68N) in the fusion (F) protein, which has been associated with reduced susceptibility to nirsevimab (MEDI8897), a novel RSV monoclonal antibody under development. In addition, several minor variants were identified in the antigenic sites of the F protein, one of which may confer resistance to palivizumab, the only licensed RSV monoclonal antibody. The differences in within-host virus populations emphasise the importance of monitoring for vaccine efficacy and may help to explain the different prevalences of monoclonal antibody-escape mutants between the two subgroups.
Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental ...remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization study of these materials using a battery of complementary techniques was performed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS), photoluminescence spectroscopy (PL) and UV–Visible absorption spectroscopy were used to evaluate the effect of Ce ions on the structural, morphological, optical and photocatalytic properties of the prepared ZnO nanostructures. The XRD results showed that the obtained photocatalysts were composed of hexagonal, wurtzite type crystallites in the 34–44 nm size range. The SEM and TEM showed nanosheet-shaped crystallites, a significant fraction of them in contact with bundles of randomly oriented and much smaller nanoparticles of a mixed cerium–zinc phase with a composition close to Ce0.68Zn0.32Ox. Importantly, in clear contrast to the prevailing proposals regarding this type of materials, the STEM-XEDS characterization of the photocatalyst samples revealed that Ce did not incorporate into the ZnO crystal lattice as a dopant but that a heterojunction formed between the ZnO nanosheets and the Ce–Zn mixed oxide phase nanoparticles instead. These two relevant compositional features could in fact be established thanks to the particular morphology obtained by the use of the microwave-assisted hydrothermal synthesis. The optical study revealed that in the ZnO:Ce samples optical band gap was found to decrease to 3.17 eV in the samples with the highest Ce content. It was also found that the ZnO:Ce (2 at.%) sample exhibited the highest photocatalytic activity for the degradation of methylene blue (MB), when compared to both the pure ZnO and commercial TiO2-P25 under simulated sunlight irradiation. The kinetics of MB photodegradation in the presence of the different photocatalysts could be properly described using a Langmuir–Hinshelwood (LH) model, for which the ZnO:Ce (2 at.%) sample exhibited the highest value of effective kinetic constant.
This research has been conducted to characterize and validate resistive heating as a synthesis method for zirconium oxides (ZrO2). A wire of Zr has been oxidized to form a core–shell structure, in ...which the core is a metal wire, and the shell is an oxide layer that is around 10 μm thick. The characterization of the samples has been performed by means of several techniques based on Scanning Electron Microscopy (SEM). The topography images show that thermal gradient appears to have little influence on morphology, unlike time, which plays an important role. The chemical composition was analyzed by X-ray spectroscopy (EDX) and X-ray diffraction (XRD), and Raman spectroscopy has been used to assess crystallinity and crystal structure. The oxide layer is mainly formed by monoclinic ZrO2, alongside other, less significant, phases. Photoluminescence (PL) and cathodoluminescence (CL) measurements have allowed us to study the distribution of defects along the shell and to confirm the degree of uniformity. The oxygen vacancies, either as isolated defects or forming complexes with impurities, play a determinant role in the luminescent processes. Color centers, mainly electron centers such as F, FA and FAA, give rise to several visible emissions extending from blue to green, with main components at around 2 eV, 2.4–2.5 eV and 2.7 eV. The differences between PL and CL in relation to distinct recombination paths are also discussed.
This paper reports on the synthesis of Ce-doped ZnO (CZO) nanoparticles (NPs) by an alternative polyol method at low temperature. The method, facile and rapid, uses acetate-based precursors, ethylene ...glycol as solvent, and polyvinylpyrrolidone as capping agent. The effects of the Ce-doping concentration (ranging from 0 to 8.24 atomic%) on the structural, morphological, compositional, optical, luminescence, and photocatalytic properties of the NPs were investigated by several techniques. The structural findings confirmed that the CZO NPs have a typical hexagonal wurtzite-type structure with a preferred orientation along the (101) plane. The results obtained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) revealed that the NPs size decreased (from ~30 to ~16 nm) with an increase in the Ce-doping concentration. Energy Dispersive X-Ray Spectroscopy (EDS) and High Resolution Transmission Microscopy (HRTEM) results confirmed the incorporation of Ce ions into the ZnO lattice. Ce-doping influences the photoluminescence (PL) emission compared to that of pure ZnO. The PL emission is related to the presence of different kinds of defects, which could take part in charge transfer and/or trapping mechanisms, hence playing an essential role in the photocatalytic activity (PCA). In fact, in this work we report an enhancement of PCA as a consequence of Ce-doping. In this sense, the best results were obtained for samples doped with 3.24 atomic%, that exhibited a photocatalytic degradation efficiency close to 99% after 60 min ultraviolet (UV) illumination, thus confirming the viability of Ce-doping for environmental applications.
PDF
