BIOSENSORS FOR GLUCOSE NEEDLE-SHAPED FOR IN-VIVO MONITORING

Different procedures for obtaining a needle biosensor for the determination of glucose to be inserted subcutaneously in vivo, have been compared. Platinum wires with a diameter of 75 mum, teflon-coated were inserted in hypodermic needles and fixed with a two-component epoxy resin. Using a dip-coating procedure, several layers were deposited on electrodes. The first coating was cellulose acetate, the second was immobilized glucose oxidase (GOD) mixed with bovine serum albumin (BSA) and glutaraldheyde, the third coating was a polyurethane coating obtained with commercially available products. A large number of electrodes have been tried and statistically evaluated but they seem to be affected by poor reproducibility evidenced by a large spreading in successive calibration curves. Then, the polyurethane coating has been replaced by a thin polycarbonate membrane salinized and fixed on the tip of the needle. Reproducible results were achieved and first results of in vivo measurements on rabbits are reported.

Sol-gel Er-doped SiO(2)-HfO(2) planar waveguides: A viable system for 1.5 mu m application

70SiO(2)-30HfO(2) planar waveguides, doped with Er(3+) concentrations ranging from 0.3 to 1 mol %, were prepared by sol-gel route, using dip-coating deposition on silica glass substrates. The waveguides show high densification degree, effective intermingling of the two components of the film, and uniform surface morphology. Propagation losses of about 1 dB/cm were measured at 632.8 nm. When pumped with 987 or 514.5 nm continuous-wave laser light, the waveguides show the (4)I(13/2)-->(4)I(15/2) emission band with a bandwidth of 48 nm. The spectral features are found independent both on erbium content and excitation wavelength. The (4)I(13/2) level decay curves presented a single-exponential profile, with a lifetime between 2.9 and 5.0 ms, depending on the erbium concentration. (C) 2002 American Institute of Physics.

Infrared-to-visible CW frequency upconversion in erbium activated silica-hafnia waveguides prepared by sol-gel route

70SiO(2)-30HfO(2) mol% planar waveguides, doped with Er3+ with concentrations ranging from 0.3 to 2 mol% were prepared by sol-gel route, using dip-coating deposition on vitreous-SiO2 substrates. Infrared-to-visible upconversion emission, upon excitation at 980 nm, has been observed for all the samples. The upconversion results in green, red and blue emissions. The investigation of the upconversion dynamic as a function of the Er3+ concentration and excitation power, show that processes such as excited state absorption and energy transfer upconversion are effective. (C) 2003 Elsevier B.V. All rights reserved.

Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron (R) modified tin oxide layer prepared by the sol-gel process

In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO2 layer was deposited by the solgel dip-coating process in the presence of Tiron (R) as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO2-coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time. (c) 2006 Elsevier B.V. All rights reserved.

EXAFS investigation on Sb incorporation effects to electrical transport in SnO2 thin films deposited by sot-gel

The effect of Sb doping in SnO2 thin films prepared by the sol-gel dip-coating (SGDC) process is investigated. Electronic and structural properties are evaluated through synchrotron radiation measurements by EXAFS and XANES. These data indicate that antimony is in the oxidation state W, and replaces tin atoms (Sn4+), at a grain surface site. Although the substitution yields net free carrier concentration, the electrical conductivity is increased only slightly, because it is reduced by the high grain boundary scattering. The overall picture leads to a shortening of the grain boundary potential, where oxygen vacancies compensate for oxygen adsorbed species, decreasing the trapped charge at grain boundary. (c) 2007 Elsevier Ltd. All rights reserved.

Rare earth doped synthetic opals and inverse opals

Monodisperse spheres of silica and latex were obtained by a surfactant free styrene polimerization and the Stober method respectively. Controlling settling either by centrifugation or by dip-coating colloidal crystals could be obtained. Silica inverse opals were prepared by using the latex colloidal crystals as templates and TEOS/ethanol solution. Eu3+ containing silica spheres were obtained dispersing silica spheres in Eu(NO3)(3) isopropanol solutions. Emission spectra suggest the formation of an amorphous Eu3+ containing phase well adhered at the spheres surface. The utilization of solutions of trifluoroacetates salts of Pb2+ and Eu3+ was observed to destroy the silica spherical pattern when samples are treated at 1000degreesC. In that case nanocrystals of PbF2 and amorphous silica were obtained after heat treatment.

XPS study on water corrosion of fluorzirconate glasses and their protection by a layer of surface modified tin dioxide nanoparticles

The surface corrosion process associated with the hydrolysis of fluorozirconate glass, Z-BLAN (53ZrF(4), 20BaF(2), 20NaF, 4LaF(2), 3AlF(3)), and the corrosion protection efficiency of a nanocrystalline transparent SnO2 layer were investigated by X-ray photoelectron spectroscopy. The tin oxide film was deposited by the sol-gel dip-coating process in the presence of Tiron(R) as particle surface modifier agent. The chemical bonding structure and composition of the surface region of coated and non-coated ZBLAN were studied before water contact and after different immersion periods (5-30 min). In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species inducing the formation of a new surface phase consisting of stable zirconium oxyfluoride, barium fluoride and lanthanum fluoride species, the results for the SnO2-coated glass showed that the hydrolytic attack induces a filling of the film nanopores by dissolved glass material and the formation of tin oxylluoride and zirconium oxyfluoride species. This process results in a modified film, which acts as a hermetic diffusion barrier protecting efficiently the glass surface. (C) 2006 Elsevier B.V. All rights reserved.

Sol-gel Eu3+/Tm3+ doped transparent glass-ceramic waveguides

Eu3+ and Tm3+ doped lanthanum fluoride and lanthanum oxyfluoride are obtained from Eu3+, Tm3+ containing lanthanum fluoracetate solutions. The nature of the crystal phase obtained could be controlled by the temperature of heat treatment. Spectral characteristics of Eu3+ doped crystal phases were sufficiently different to allow utilization of Eu3+ as structural probes. Tm3+ emission at the technologically important spectral region of 1450nm could be observed for the fluoride and oxyfluoride crystal phases. The large bandwidth obtained (around 120nm) suggests potential applications in optical amplification. SiO2-LaF3-LaOF composite materials were also prepared. It is observed that for heat treatments above 800degreesC, fluorine loss, probably in the form of SiF4 hinder the observation of Tm3+ emission. Eu3+ spectroscopic characteristics clearly show the evolution of a fluoride like environment to an amorphous oxide one as the temperature of heat treatment increased. Thin films obtained by dip-coating on V-SiO2 substrates and treated at 300degreesC, 500degreesC and 800degreesC display guided modes in the visible and infrared regions. Optical characteristics (refractive index and films thickness) were obtained at 543.5, 632.8 and 1550nm. Attenuation as low as 1.8dB/cm was measured at 632.8nm. (C) 2004 Published by Elsevier B.V.

Dielectric properties and microstructure of SrTiO3/BaTiO3 multilayer thin films prepared by a chemical route

Multilayer thin films with perovskite structures were produced by the polymeric precursor method. SrTiO3/BaTiO3 (STO/BTO) multilayers were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the spin-coating technique and heated in air at 700 degreesC. The microstructure and crystalline phase of the multilayered thin films were examined by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), resolution-high transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and X-ray diffraction. The SrTiO3/BaTiO3 multilayer thin films consisted of grainy structures with an approximate grain size of 60 nm. The multilayered thin films showed a very clear interface between the components. The SrTiO3/BaTiO3 multilayer thin films revealed dielectric constants of approximately 527 and loss tangents of 0.03 at 100 kHz. The dielectric constant calculated for this multilayer film system is the value of the sum of each individual component of the film, i.e. The total value of the sum of each SrTiO3 (STO) and BaTiO3 (BTO) layer. The multilayer SrTiO3/BaTiO3 obtained by the polymeric precursor method, also showed a ferroelectric behavior with a remanent polarization of 2.5 muC/cm(2) and a coercive field of 30 kV/cm. The multilayer films displayed good fatigue characteristics under bipolar stressing after application of 10(10) switching cycles. (C) 2001 Published by Elsevier B.V. B.V. All rights reserved.

Improvement of the corrosion resistance of polysiloxane hybrid coatings by cerium doping

Polysiloxane hybrid films were deposited on stainless steel by dip-coating using a sol prepared by hydrolytic co-polycondensation of tetraethoxysilane (TEOS) and 3-methacryloxy propyltrimethoxysilane (MPTS), followed by radical polymerization of methacrylic moieties. The TEOS/MPTS ratio was chosen equal to 2 and the Ce/Si ratio varied between 0.01 and 0.1. The effects of cerium concentration and valence (Ce(III) and Ce (IV)) on the structural features of polysiloxane films were studied by X-ray photoelectron spectroscopy (XPS) and (29)Si nuclear magnetic resonance (NMR). The corrosion protection of stainless steel by the hybrid coatings was investigated by XPS, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves, after immersion in saline and acid solutions. The NMR results have shown for Ce(IV) doped films a high degree of polycondensation of up to 89%. Electrochemical analysis has evidenced that hybrid films with the lowest Ce concentration act as an efficient diffusion barrier by increasing the corrosion resistance and reducing the current densities up to 3 orders of magnitude compared to bare stainless steel. The analysis of structural effects induced by Ce(III) and Ce(IV) species, performed by XPS, indicates that the improved corrosion protection of Ce(IV) doped films might be mainly related to the enhanced polymerization of siloxane groups. (C) 2010 Elsevier B.V. All rights reserved.

Corrosion protection of stainless steel by polysiloxane hybrid coatings prepared using the sol-gel process

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Leakage current, ferroelectric and structural properties in Pb(1-x)Ba(x)TiO(3) thin films prepared by chemical route

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

LiNbO3 thin films prepared from a polymeric precursor method

LiNbO3 thin films were prepared from polymeric precursor method by dip coating. The precursor films, deposited on Si(111) substrates, were heat-treated from 400°C to 900°C in order to study the heat treatment influence on the crystallinity and microstructure of the final film. The X-ray diffraction patterns showed, in particular, that these films crystallize at low temperature (450°C) and present no preferential orientation. The scanning electron microscopy studies showed that the film microstructure is strongly influenced by the annealing temperature. © 1997 Trans Tech Publications.

Structural and surface morphology characterizations of oriented LiNbO3 thin films grown by polymeric precursor method

Polymeric precursor solution was used to deposit LiNbO3 thin films by dip coating on sapphire substrates. The effects of processing variables, such as heat treatment conditions and number of deposited layers, on crystallinity and morphology of the final films were investigated. X-ray diffraction patterns show the oriented growth of the films. The rocking curves, obtained around the (006) LiNbO3 peak, revealed that the shape peak and the FWHM value were influenced by the processing variables. According to these parameters, some films presented very homogeneous dense and smooth surfaces, as shown by the SEM and AFM studies.

Influence of heat treatment on LiNbO3 thin films prepared on Si(111) by the polymeric precursor method

The effects of heat-treatment temperature on LiNbO3 thin films prepared by the polymeric precursor method were investigated. The precursor solution was deposited on Si(111) substrates by dip coating. X-ray diffraction and thermal analyses revealed that the crystallization process occurred at a low temperature (420 °C) and led to films with no preferential orientation. High-temperature treatments promoted formation of the LiNb3O8 phase. Scanning electron microscopy, coupled with energy dispersive spectroscopy analyses, showed that the treatment temperature also affected the film microstructure. The surface texture - homogeneous, smooth, and pore-free at low temperature - turned into an `islandlike' microstructure for high-temperature treatments.