P.A. Carvalho

Star-shaped magnetite@gold nanoparticles for protein magnetic separation and SERS detection

A novel synthetic methodology for star shaped gold-coated magnetic nanoparticles is reported. The coating is performed in two steps: formation of gold nuclei at the surface of magnetite nanoparticles followed by growth of the gold nuclei into a complete star shaped shell. The star-shaped gold-coated magnetic nanoparticles thus obtained preserve the magnetic properties of the precursor magnetite nanoparticles, e.g. they can be easily separated with a magnet. In addition, the gold coating provides interesting optical properties while simultaneously allowing for biofunctionalization that may be advantageous for biological applications, such as (bio)detection via surface-enhanced Raman spectroscopy (SERS). As a proof-of-concept, a capping agent terminated with a nickel(II)-nitrilotriacetate group showing high affinity for histidine was used to modify the surface of the nanoparticles. The resulting star-shaped nanoparticles were used to selectively capture histidine-tagged maltose-binding protein from a crude cell extract. Finally, the performance of star shaped gold-coated magnetic nanoparticles as SERS platforms was demonstrated through the detection of Raman active dye (Astra Blue).

Docosahexaenoic Acid Inhibits Helicobacter pylori Growth In Vitro and Mice Gastric Mucosa Colonization

H. pylori drug-resistant strains and non-compliance to therapy are the major causes of H. pylori eradication failure. For some bacterial species it has been demonstrated that fatty acids have a growth inhibitory effect. Our main aim was to assess the ability of docosahexaenoic acid (DHA) to inhibit H. pylori growth both in vitro and in a mouse model. The effectiveness of standard therapy (ST) in combination with DHA on H. pylori eradication and recurrence prevention success was also investigated. The effects of DHA on H. pylori growth were analyzed in an in vitro dose-response study and n in vivo model. We analized the ability of H. pylori to colonize mice gastric mucosa following DHA, ST or a combination of both treatments. Our data demonstrate that DHA decreases H. pylori growth in vitro in a dose-dependent manner. Furthermore, DHA inhibits H. pylori gastric colonization in vivo as well as decreases mouse gastric mucosa inflammation. Addition of DHA to ST was also associated with lower H. pylori infection recurrence in the mouse model. In conclusion, DHA is an inhibitor of H. pylori growth and its ability to colonize mouse stomach. DHA treatment is also associated with a lower recurrence of H. pylori infection in combination with ST. These observations pave the way to consider DHA as an adjunct agent in H. pylori eradication treatment.

New insights into the use of magnetic force microscopy to discriminate between magnetic and nonmagnetic nanoparticles

Magnetic force microscopy (MFM) is a very powerful technique, which can potentially be used to detect and localize the magnetic fields arising from nanoscopic magnetic domains, such as magnetic nanoparticles. However, in order to achieve this, we must be able to use MFM to discriminate between magnetic forces arising from the magnetic nanoparticles and nonmagnetic forces from other particles and sample features. Unfortunately, MFM can show a significant response even for nonmagnetic nanoparticles, giving rise to potentially misleading results. The literature to date lacks evidence for MFM detection of magnetic nanoparticles with nonmagnetic nanoparticles as a control. In this work, we studied magnetite particles of two sizes and with a silica shell, and compared them to nonmagnetic metallic and silica nanoparticles. We found that even on conducting, grounded substrates, significant electrostatic interaction between atomic force microscopy probes and nanoparticles can be detected, causing nonmagnetic signals that might be mistaken for a true MFM response. Nevertheless, we show that MFM can be used to discriminate between magnetic and nonmagnetic nanoparticles by using an electromagnetic shielding technique or by analysis of the phase shift data. On the basis of our experimental evidence we propose a methodology that enables MFM to be reliably used to study unknown samples containing magnetic nanoparticles, and correctly interpret the data obtained.

Automated workstation for variable composition laser cladding : its use for rapid alloy scanning

Abstract An automated workstation for variable composition laser cladding was developed and its potential for rapid alloy scanning was demonstrated. Ternary alloys of the CoNiAl system were prepared using variable powder feed rates: the aim was to produce linear composition variations along the length of the laser-clad tracks. The chemical compositions and the hardnesses of the alloys corresponding to different zones of the tracks were evaluated. Microstructural characterization was performed by scanning electron microscopy and X-ray diffraction. To assess the corrosion behaviour of the alloys, electrochemical polarization tests were carried out in aerated 3% NaCl. The deviations from linearity of the composition variations were explained, the microstructure evolution was studied, a relationship between the hardness and the microstructure was found, and some trends in the corrosion behaviour were defined.

Impact of different confinement regimes on the two-dimensional structure of edge turbulence

This paper reports the impact of different confinement regimes on the 2D structure of edge turbulence. An image analysis method based on two-dimensional continuous wavelet transformation is used to localize structures (blobs) in the images and to extract their geometrical characteristics (position, scale, orientation angle and aspect ratio). We study the impact of edge shear-layers on these geometrical aspects of blobs. Results show a reduction in the angular dispersion of blobs as the shear layer is established in the boundary, as well as an increase in the elongation of these structures. Similar behaviour is found in NSTX image sequences when going from L to H mode plasmas. During improved confinement regimes the number of detected blobs decreases. Some indications are found suggesting that the turbulence reduction could be scale-selective in the biasing-induced improved confinement regime of TJ-II stellarator. Perpendicular flow reversal is visualized with the cameras and the time scales for flow reversal are found to be less than 50 µs. Radially propagating structures are found in the SOL with velocities in the range ~1000 m/s and with a poloidally asymmetric spatial distribution.

A protection system for the JET ITER-like wall based on imaging diagnostics

The new JET ITER-like wall (made of beryllium and tungsten) is more fragile than the former carbon fiber composite wall and requires active protection to prevent excessive heat loads on the plasma facing components (PFC). Analog CCD cameras operating in the near infrared wavelength are used to measure surface temperature of the PFCs. Region of interest (ROI) analysis is performed in real time and the maximum temperature measured in each ROI is sent to the vessel thermal map. The protection of the ITER-like wall system started in October 2011 and has already successfully led to a safe landing of the plasma when hot spots were observed on the Be main chamber PFCs. Divertor protection is more of a challenge due to dust deposits that often generate false hot spots. In this contribution we describe the camera, data capture and real time processing systems. We discuss the calibration strategy for the temperature measurements with cross validation with thermal IR cameras and bi-color pyrometers. Most importantly, we demonstrate that a protection system based on CCD cameras can work and show examples of hot spot detections that stop the plasma pulse. The limits of such a design and the associated constraints on the operations are also presented.

Isothermal section at 750°C of the U–Fe–Sn ternary system

A systematic investigation of the isothermal section at 850 8C of the U–Fe–Al ternary system was done by means of scanning electron microprobe analysis and X-ray powder diffraction. At this temperature the phase diagram is characterized by the formation of seven ternary phases and two extended ranges of solubility. Three compounds form with non-existing, or negligible, homogeneity domains: UFe2Al10 (YbFe2Al10-type, aZ8.9146(3) A u , bZ10.1986(3) A u , cZ9.0114(3) A u ); U2Fe3.6Al13.4 (Th2Ni17-type, aZ8.8589(2) A u , cZ8.9824(2) A u ); and U2Fe12Al5 (Th2Ni17-type, aZ8.5631(7) A u , cZ8.438(1) A u ). Four other phases exhibit more or less extended homogeneity ranges: UFe1CxAl1Kx (MgZn2-type); U3Fe4CxAl12Kx (Gd3Ru4Al12-type); U2Fe17KxAlx (Th2Zn17-type); and UFexAl12Kx (ThMn12-type). The two extended solid solutions, UAl2KxFex and UFe2KxAlx, are formed from the UAl2 and UFe2 binary compounds, respectively, both crystallizing in the cubic MgCu2-type structure. q 2004 Elsevier Ltd. All rights reserved.

HRTEM study of Co7W6 and its typical defect structure

The tetrahedrally close-packed structure of Co7W6 (m-phase) was studied by HRTEM. A mas- sive presence of random sub-unit cell twins was detected. These planar defects were characterized in detail and the twinning probability at potential mirror planes was established. High-precision image simulation of the bulk structure and defect region was performed, using a simulated evolution optimization strategy to refine the imaging conditions. Ab initio calculations were carried out in order to determine the energy involved in twinning, as well as the distortion induced in the structure. 7 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.

Cytoadherence of erythrocytes invaded by Plasmodium falciparum: Quantitative contact-probing of a human malaria receptor

Cytoadherence of red blood cells (RBCs) invaded by Plasmodium falciparum parasites is an important contributor to the sequestration of RBCs, causing reduced microcirculatory flow associated with fatal malaria syndromes. The phenomenon involves a parasite-derived variant antigen, the P. falciparum erythrocyte membrane protein 1 (PfEMP1), and several human host receptors, such as chondroitin sulfate A (CSA), which has been explicitly implicated in placental malaria. Elucidating the molecular mechanisms of cytoadherence requires quantitative evaluation, under physiologically relevant conditions, of the specific receptor-ligand interactions associated with pathological states of cell-cell adhesion. Such quantitative studies have not been reported thus far for P. falciparum malaria under conditions of febrile temperatures that accompany malarial infections. In this study, single RBCs infected with P. falciparum parasites (CSA binding phenotype) in the trophozoite stage were engaged in mechanical contact with the surface of surrogate cells specifically expressing CSA, so as to quantify cytoadherence to human syncytiotrophoblasts in a controlled manner. From these measurements, a mean rupture force of 43pN was estimated for the CSA-PfEMP1 complex at 37°C. Experiments carried out at febrile temperature showed a noticeable decrease in CSA-PfEMP1 rupture force (by about 23% at 41°C and about 20% after a 40°C heat treatment), in association with an increased binding frequency. The decrease in rupture force points to a weakened receptor-ligand complex after exposure to febrile temperature, while the rise in binding frequency suggests an additional display of nonspecific binding molecules on the RBC surface. The present work establishes a robust experimental method for the quantitative assessment of cytoadherence of diseased cells with specific molecule-mediated binding.

Cu2O polyhedral nanowires produced by microwave irradiation

The present work reports the oxidation of copper nanowires via microwave irradiation under wet conditions. Structural characterization of the nanowires has been carried out by X-ray diffraction, transmission electron microscopy and scanning electron microscopy coupled with focused ion beam, electron backscatter diffraction and energy dispersive X-ray spectroscopy. The copper nanowires were essentially monocrystalline with 〈110〉 axes, albeit growth twins have also been observed. Oxidation of the metal nanowires resulted in the growth of polyhedral Cu2O crystals arranged in twinned configurations around the nanowire axis. The crystallographic orientation of the twin variants is compatible with a cube-on-cube orientation relation originating from the epitaxial growth of Cu2O from pure Cu.