High-surface thermally stable mesoporous gallium phosphates constituted by nanoparticles as primary building blocks

In constant, search for micro/mesoporous materials, gallium phosphates, have attracted continued interest due to the large pore size reported for some of these solids in comparison with analogous aluminum phosphates. However up to now, the porosity of gallium phosphates collapsed upon template removal or exposure to the ambient moisture. In the present work, we describe high-surface thermally stable mesoporous gallium phosphates synthesized from gallium propoxide and PCl3 and different templating agents such as amines (dipropylamine, piperidine and aminopiperidine) and quaternary ammonium salts (C16H33(CH3)3NBr and C16PyCl). These highly reactive precursors have so far not been used as gallium and phosphate sources for the synthesis of gallophosphates. Conceptually, our present synthetic procedure is based on the fast formation of gallium phosphate nanoparticles via the reaction of gallium propoxide with PCl3 and subsequent construction of the porous material with nanoparticles as building blocks. The organization of the gallophosphate nanoparticles in stable porous structures is effected by the templates. Different experimental procedures varying the molar composition of the sol-gel, pH and the pretreatment of gallium precursor were assayed, most of them leading to satisfactory materials in terms of thermal stability and porosity. In this way, a series of gallium phosphates with surface are above 200 m(2) g(-1), and narrow pore size from 3 to 6 nm and remarkable thermal stability (up to 550 degrees C) have been prepared. In some cases, the structure tends to show some periodicity and regularity as determined by XRD. The remarkable stability has allowed us to test the catalytic activity of gallophosphates for the aerobic oxidation of alkylaromatics with notable good results. Our report reopens the interest for gallophosphates in heterogeneous catalysis. (C) 2010 Elsevier Inc. All rights reserved.

Standardisation and comparison of methods employed for microbial cell surface hydrophobicity and charge determination

Whilst there are a number of methods available to characterise the cell surface hydrophobicity (CSH) and cell surface charge (CSC) of microorganisms, there is still debate concerning the correlation of results between individual methods. In this study, the techniques of bacterial adherence to hydrocarbons (BATH) and hydrophobic interaction chromatography (HTC) were used to measure CSH. Electrostatic interaction chromatography (ESIC) and zeta potential (ZP) measurements were used to determine CSC. To allow meaningful comparisons between the BATH and HIC tests, between ESIC and ZP and also between CSH and CSC, the buffer systems employed in each test were standardised (phosphate buffered saline, pH 7.3, 0.01 mM). Isolates of Staphylococcus epidermidis derived from microbial biofilm were used as the test organism in this study. The isolates examined exhibited primarily medium to high CSH and a highly negative CSC. Good correlation of CSH measurement was observed between the BATH and HIC tests (r = 0.89). Good correlation was observed between ESIC (anionic exchange column) and ZP measurements. No correlations were observed between isolate CSC and either increased or decreased CSH. It is recommended that whenever comparisons of various methods to determine either CSC or CSH (by partitioning methods), the buffer systems should remain constant throughout to achieve consistency of results.

Label-free detection of nanomolar unmodified single- and double-stranded dna by using surface-enhanced raman spectroscopy on Ag and Au colloids

Unlabelled single- and double-stranded DNA (ssDNA and dsDNA, respectively) has been detected at concentrations =10-9?M by surface-enhanced Raman spectroscopy. Under appropriate conditions the sequences spontaneously adsorbed to the surface of both Ag and Au colloids through their nucleobases; this allowed highly reproducible spectra with good signal-to-noise ratios to be recorded on completely unmodified samples. This eliminated the need to promote absorption by introducing external linkers, such as thiols. The spectra of model ssDNA sequences contained bands of all the bases present and showed systematic changes when the overall base composition was altered. Initial tests also showed that small but reproducible changes could be detected between oligonucleotides with the same bases arranged in a different order. The spectra of five ssDNA sequences that correspond to different strains of the Escherichia coli bacterium were found to be sufficiently composition-dependent so that they could be differentiated without the need for any advanced multivariate data analysis techniques.

Polarisation independent split ring frequency selective surface

A frequency selective surface (FSS) is described which exhibits coincident spectral responses for TE and TM polarisation when the FSS operates at 45 degrees incidence. The structure consists of two closely spaced arrays of ring elements with the conductor split at one or two locations to provide independent control of the resonances for the vertical and horizontal field directions. The FSS is designed to diplex two channels separated by an edge of a band ratio of 1.7:1 and yield a common - 10 dB reflection bandwidth of 10.2%. Measured and numerical results are shown to be in good agreement over the frequency range 9-12 GHz.

The development of a surface defect machining method for hard turning processes

Hard turning (HT) is a material removal process employing a combination of a single point cutting tool and high speeds to machine hard ferrous alloys which exhibit hardness values over 45 HRC. In this paper, a surface defect machining (SDM) method for HT is proposed which harnesses the combined advantages of porosity machining and pulsed laser pre-treatment processing. From previous experimental work, this was shown to provide better controllability of the process and improved quality of the machined surface. While the experiments showed promising results, a comprehensive understanding of this new technique could only be achieved through a rigorous, in depth theoretical analysis. Therefore, an assessment of the SDM technique was carried out using both finite element method (FEM) and molecular dynamics (MD) simulations.
FEM modelling was used to compare the conventional HT of AISI 4340 steel (52 HRC) using an Al2O3 insert with the proposed SDM method. The simulations showed very good agreement with the previously published experimental results. Compared to conventional HT, SDM provided favourable machining outcomes, such as reduced shear plane angle, reduced average cutting forces, improved surface roughness, lower residual stresses on the machined surface, reduced tool–chip interface contact length and increased chip flow velocity. Furthermore, a scientific explanation of the improved surface finish was revealed using a state-of-the-art MD simulation model which suggested that during SDM, a combination of both the cutting action and rough polishing action help improve the machined surface finish.

Structure and dynamics of dextran in binary mixtures of a good and a bad solvent

The structure and dynamics of the common polysaccharide dextran have been investigated in mixed solvents at two different temperatures using small-angle X-ray scattering (SAXS) and viscosity measurements. More specifically, binary mixtures of a good solvent (water, formamide, dimethylsulfoxide, ethanolamine) and the bad solvent ethanol as the minority component have been considered. The experimentally observed effects on the polymer conformation (intrinsic viscosity, coil radius, and radius of gyration) of the bad solvent addition are discussed in terms of hydrogen bonding density and are correlated with the Hansen solubility parameters and the surface tension of the solvent mixtures. Hydrogen bonding appears to be an important contributor to the solubility of dextran but is not sufficient to capture the dextran coil contraction in the mixtures of good+bad solvents.

Detection of Tetrodotoxins in Puffer Fish by a Self-Assembled Monolayer-Based Immunoassay and Comparison with Surface Plasmon Resonance, LC-MS/MS, and Mouse Bioassay

The increasing occurrence of puffer fish containing tetrodotoxin (TTX) in the Mediterranean could represent a major food safety risk for European consumers and threaten the fishing industry. The work presented herein describes the development of a new enzyme linked immunosorbent assay (mELISA) based on the immobilization of TTX through dithiol monolayers self-assembled on maleimide plates, which provides an ordered and oriented antigen immobilization and favors the antigen-antibody affinity interaction. The mELISA was found to have a limit of detection (LOD) of TTX of 0.23 mg/kg of puffer fish matrix. The mELISA and a surface plasmon resonance (SPR) immunosensor previously developed were employed to establish the cross-reactivity factors (CRFs) of 5,6,11-trideoxy-TTX, 5,11-deoxy-TTX, 11-nor-TTX-6-ol, and 5,6,11-trideoxy-4-anhydro-TTX, as well as to determine TTX equivalent contents in puffer fish samples. Results obtained by both immunochemical tools were correlated (R(2) = 0.977). The puffer fish samples were also analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the corresponding CRFs were applied to the individual TTX contents. Results provided by the immunochemical tools, when compared with those obtained by LC-MS/MS, showed a good degree of correlation (R(2) = 0.991 and 0.979 for mELISA and SPR, respectively). The mouse bioassay (MBA) slightly overestimated the CRF adjusted TTX content of samples when compared with the data obtained from the other techniques. The mELISA has been demonstrated to be fit for the purpose for screening samples in monitoring programs and in research activities.

Alkali-free bioactive glasses for bone regeneration

Bioactive glasses and glass-ceramics are a class of third generation biomaterials which elicit a special response on their surface when in contact with biological fluids, leading to strong bonding to living tissues. The purpose of the present study was to develop diopside based alkali-free bioactive glasses in order to achieve good sintering behaviour, high bioactivity, and a dissolution/ degradation rates compatible with the target applications in bone regeneration and tissue engineering. Another aim was to understand the structure-property relationships in the investigated bioactive glasses. In this quest, various glass compositions within the Diopside (CaMgSi2O6) – Fluorapatite (Ca5(PO4)3F) – Tricalcium phosphate (3CaO•P2O5) system have been investigated. All the glasses were prepared by melt-quenching technique and characterized by a wide array of complementary characterization techniques. The glass-ceramics were produced by sintering of glass powders compacts followed by a suitable heat treatment to promote the nucleation and crystallization phenomena. Furthermore, selected parent glass compositions were doped with several functional ions and an attempt to understand their effects on the glass structure, sintering ability and on the in vitro bio-degradation and biomineralization behaviours of the glasses was made. The effects of the same variables on the devitrification (nucleation and crystallization) behaviour of glasses to form bioactive glass-ceramics were also investigated. Some of the glasses exhibited high bio-mineralization rates, expressed by the formation of a surface hydroxyapatite layer within 1–12 h of immersion in a simulated body fluid (SBF) solution. All the glasses showed relatively lower degradation rates in comparison to that of 45S5 Bioglass®. Some of the glasses showed very good in vitro behaviour and the glasses co-doped with zinc and strontium showed an in vitro dose dependent behaviour. The as-designed bioactive glasses and glass–ceramic materials are excellent candidates for applications in bone regeneration and for the fabrication of scaffolds for tissue engineering.

Surface reactivity enhancement of silica-based glass-ceramic scaffolds

A paradigm shift is taking place from using transplanting tissue and synthetic implants to a tissue engineering approach that aims to regenerate damaged tissues by combining cells from the body with highly porous scaffold biomaterials, which act as templates, guiding the growth of new tissue. The central focus of this thesis was to produce porous glass and glass-ceramic scaffolds that exhibits a bioactive and biocompatible behaviour with specific surface reactivity in synthetic physiological fluids and cell-scaffold interactions, enhanced by composition and thermal treatments applied. Understanding the sintering behaviour and the interaction between the densification and crystallization processes of glass powders was essential for assessing the ideal sintering conditions for obtaining a glass scaffolds for tissue engineering applications. Our main goal was to carry out a comprehensive study of the bioactive glass sintering, identifying the powder size and sintering variables effect, for future design of sintered glass scaffolds with competent microstructures. The developed scaffolds prepared by the salt sintering method using a 3CaO.P2O5 - SiO2 - MgO glass system, with additions of Na2O with a salt, NaCl, exhibit high porosity, interconnectivity, pore size distribution and mechanical strength suitable for bone repair applications. The replacement of 6 % MgO by Na2O in the glass network allowed to tailor the dissolution rate and bioactivity of the glass scaffolds. Regarding the biological assessment, the incorporation of sodium to the composition resulted in an inibition cell response for small periods. Nevertheless it was demonstrated that for 21 days the cells response recovered and are similar for both glass compositions. The in vitro behaviour of the glass scaffolds was tested by introducing scaffolds to simulated body fluid for 21 days. Energy-dispersive Xray spectroscopy and SEM analyses proved the existence of CaP crystals for both compositions. Crystallization forming whitlockite was observed to affect the dissolution behaviour in simulated body fluid. By performing different heat treatments, it was possible to control the bioactivity and biocompatability of the glass scaffolds by means of a controlled crystallization. To recover and tune the bioactivity of the glass-ceramic with 82 % crystalline phase, different methods have been applied including functionalization using 3- aminopropyl-triethoxysilane (APTES). The glass ceramic modified surface exhibited an accelerated crystalline hydroxyapatite layer formation upon immersion in SBF after 21 days while the as prepared glass-ceramic had no detected formation of calcium phosphate up to 5 months. A sufficient mechanical support for bone tissue regeneration that biodegrade later at a tailorable rate was achievable with the glass–ceramic scaffold. Considering the biological assessment, scaffolds demonstrated an inductive effect on the proliferation of cells. The cells showed a normal morphology and high growth rate when compared to standard culture plates. This study opens up new possibilities for using 3CaO.P2O5–SiO2–MgO glass to manufacture various structures, while tailoring their bioactivity by controlling the content of the crystalline phase. Additionally, the in vitro behaviour of these structures suggests the high potential of these materials to be used in the field of tissue regeneration.

Artificial antibodies for troponin T by its imprinting on the surface of multiwalled carbon nanotubes: Its use as sensory surfaces

A novel artificial antibody for troponin T (TnT) was synthesized by molecular imprint (MI) on the surface of multiwalled carbon nanotubes (MWCNT). This was done by attaching TnT to the MWCNT surface, and filling the vacant spaces by polymerizing under mild conditions acrylamide (monomer) in N,N′-methylenebisacrylamide (cross-linker) and ammonium persulphate (initiator). After removing the template, the obtained biomaterial was able to rebind TnT and discriminate it among other interfering species. Stereochemical recognition of TnT was confirmed by the non-rebinding ability displayed by non-imprinted (NI) materials, obtained by imprinting without a template. SEM and FTIR analysis confirmed the surface modification of the MWCNT. The ability of this biomaterial to rebind TnT was confirmed by including it as electroactive compound in a PVC/plasticizer mixture coating a wire of silver, gold or titanium. Anionic slopes of 50 mV decade−1 were obtained for the gold wire coated with MI-based membranes dipped in HEPES buffer of pH 7. The limit of detection was 0.16 μg mL−1. Neither the NI-MWCNT nor the MWCNT showed the ability to recognize the template. Good selectivity was observed against creatinine, sucrose, fructose, myoglobin, sodium glutamate, thiamine and urea. The sensor was tested successfully on serum samples. It is expected that this work opens new horizons on the design of new artificial antibodies for complex protein structures.

Myoglobin-biomimetic electroactive materials made by surface molecular imprinting on silica beads and their use as ionophores in polymeric membranes for potentiometric transduction

Myoglobin (Mb) is among the cardiac biomarkers playing a major role in urgent diagnosis of cardiovascular diseases. Its monitoring in point-of-care is therefore fundamental. Pursuing this goal, a novel biomimetic ionophore for the potentiometric transduction of Mb is presented. It was synthesized by surface molecular imprinting (SMI) with the purpose of developing highly efficient sensor layers for near-stereochemical recognition of Mb. The template (Mb) was imprinted on a silane surface that was covalently attached to silica beads by means of self-assembled monolayers. First the silica was modified with an external layer of aldehyde groups. Then, Mb was attached by reaction with its amine groups (on the external surface) and subsequent formation of imine bonds. The vacant places surrounding Mb were filled by polymerization of the silane monomers 3-aminopropyltrimethoxysilane (APTMS) and propyltrimethoxysilane (PTMS). Finally, the template was removed by imine cleavage after treatment with oxalic acid. The results materials were finely dispersed in plasticized PVC selective membranes and used as ionophores in potentiometric transduction. The best analytical features were found in HEPES buffer of pH 4. Under this condition, the limits of detection were of 1.3 × 10−6 mol/L for a linear response after 8.0 × 10−7 mol/L with an anionic slope of −65.9 mV/decade. The imprinting effect was tested by preparing non-imprinted (NI) particles and employing these materials as ionophores. The resulting membranes showed no ability to detect Mb. Good selectivity was observed towards creatinine, sacarose, fructose, galactose, sodium glutamate, and alanine. The analytical application was conducted successfully and showed accurate and precise results.

Smart Plastic Antibody Material for Hemoglobin Tailored by Silica Surface Imprinting and with Charged Binding Sites: Its use as Ionophore in Potentiometric Transduction

JORNADAS DE ELECTROQUÍMICA E INOVAÇÃO 2013

Surface display of proteins by Gram-negative bacterial autotransporters

Affiliation: Faculté de Médecine Vétérinaire, Université de Montréal

Synthèse de brosses de polyélectrolytes par polymérisation initiée depuis une surface de mica et étude de leur réponse en fonction du pH et de la force ionique

Cette thèse rapporte le greffage chimique de brosses de polymères neutres de poly(acrylate de tert-butyle) (PtBA) et de brosses chargées d’acide polyacrylique (PAA) sur des substrats de mica afin d’étudier leur conformation en fonction de la densité de greffage, du pH et de la force ionique. Le greffage est réalisé par polymérisation contrôlée par transfert d’atome (ATRP) initiée depuis la surface de mica afin de contrôler la croissance du polymère et sa densité de greffage. L’étude de la conformation des brosses de PtBA et de PAA a été menée avec la technique AFM en mesurant les épaisseurs des films à sec et gonflés sous différentes conditions de solvant, de pH et de force ionique. Une monocouche d’amorceurs est tout d’abord greffée sur du mica porteur de groupes hydroxyles créés par plasma (Ar/H2O). Cette couche a été caractérisée par des mesures d’angle de contact et par la technique TOF-SIMS. L’amorceur greffé a ensuite permis d’initier l’ATRP directement depuis la surface pour former des brosses neutres de PtBA liés de façon covalente au mica. La croissance linéaire de l’épaisseur du film avec la masse molaire du polymère en solution et le taux de conversion montre que la polymérisation est contrôlée. De plus, la ré-initiation des chaînes greffées atteste du caractère vivant de la polymérisation. L’hydrolyse des brosses de PtBA, confirmée par des mesures d’angle de contact, d’épaisseur et par FT-IR, conduit à des brosses de PAA. Les différentes couches greffées sont stables à l’air, en milieu organique et en milieu aqueux et leur gonflement est réversible. Le degreffage de la couche de PAA est observé suite à une longue exposition à pH basique. Cette étude représente le premier exemple de brosses greffées chimiquement sur du mica par polymérisation initiée depuis la surface. La variation des paramètres de la réaction de greffage de l’amorceur, tels que la concentration et la durée de réaction, a permis de contrôler le taux de recouvrement de l’amorceur et la densité de greffage du polymère. Une grande gamme de taux de recouvrement de l’amorceur est accessible et se traduit par un intervalle de densités de greffage allant de faibles à élevées (e.g. 0,04 chaîne/nm2 à 0,5 chaîne/nm2). L’étude de la conformation des chaînes de PtBA dans le DMF montre que cet intervalle de densités recouvre le régime crêpe au régime brosse. Le gonflement de brosses de PAA et la variation de la hauteur de la brosse L ont été étudiés en fonction de la densité de greffage, du pH et du sel ajouté cs (NaCl). Une transition brusque de collapsée à étirée est observée avec l’augmentation du pH, indépendamment de la densité de greffage. A pH neutre, les brosses sont collapsées et se comportent comme des brosses neutres en mauvais solvant. A pH basique, les brosses sont gonflées et chargées et se trouvent dans un régime de Pincus caractéristique des polyélectrolytes forts. En présence de sel, les charges sont partiellement écrantées et les répulsions électrostatiques dominent toujours dans la brosse. Cette étude contribue à une meilleure compréhension du comportement complexe des brosses de polyélectrolytes faibles et apporte un soutien expérimental à la théorie sur le comportement de ces brosses.

A Coupled 2 × 2D Babcock–Leighton Solar Dynamo Model. I. Surface Magnetic Flux Evolution

The need for reliable predictions of the solar activity cycle motivates the development of dynamo models incorporating a representation of surface processes sufficiently detailed to allow assimilation of magnetographic data. In this series of papers we present one such dynamo model, and document its behavior and properties. This first paper focuses on one of the model's key components, namely surface magnetic flux evolution. Using a genetic algorithm, we obtain best-fit parameters of the transport model by least-squares minimization of the differences between the associated synthetic synoptic magnetogram and real magnetographic data for activity cycle 21. Our fitting procedure also returns Monte Carlo-like error estimates. We show that the range of acceptable surface meridional flow profiles is in good agreement with Doppler measurements, even though the latter are not used in the fitting process. Using a synthetic database of bipolar magnetic region (BMR) emergences reproducing the statistical properties of observed emergences, we also ascertain the sensitivity of global cycle properties, such as the strength of the dipole moment and timing of polarity reversal, to distinct realizations of BMR emergence, and on this basis argue that this stochasticity represents a primary source of uncertainty for predicting solar cycle characteristics.