D. Rabelo

Magnetic resonance of magnetite nanoparticles dispersed in mesoporous copolymer matrix

Magnetic resonance is used to investigate fine particles of magnetite (Fe/sub 3/O/sub 4/) synthesized as isolated nanoparticles (INPs) in a mesoporous styrene-divinylbenzene (Sty-DVB) copolymer template. The magnetite nanoparticles were obtained through alkaline precipitation of ferrous sulfate, at different iron (II) concentration (Q), in the sulfonated polymeric matrix. Analysis of the temperature (T) dependence of the resonance field (H/sub R/) and resonance linewidth (/spl Delta/H/sub R/) provide a useful way to estimate the average size of the magnetite nanoparticles. The data indicates that the nanoparticle average diameter (D) increases as Q increases, in accordance with the data reported previously.

Electron Microscopy Investigation of Magnetite Nanoparticles Immersed in a Polymer Template

Transmission electron microscopy and scanning electron microscopy were used to investigate chemically cycled magnetite-based composites using mesoporous sulfonated styrene-divinylbenzene copolymer as template. The micron-sized morphology of the template was investigated using scanning electron microscopy, while transmission electron microscopy provided useful information concerning the nanoparticle size polydispersity profile and location of the magnetite nanoparticles inside the template. The narrowing of the nanoparticle size distribution and the linear dependence of the magnetite mass incorporation versus number of chemical cycles are supported by the transmission electron microscopy data.

Synthesis, characterization and magnetic properties of polymer-Fe3O4 nanocomposite.

The chemical stability of magnetic particles is of great importance for their applications in medicine and biotechnology. The most challenging problem in physics of disordered systems of magnetic nanoparticles is the investigation of their dynamic properties. The chemical coprecipitation process was used to synthesize spherical magnetite nanoparticles of 14 nm. The as-prepared magnetite nanoparticles have been aged in the matrix. Magnetic properties and aging effect were studied by Mössbauer spectroscopy at temperatures ranging from 77 to 300 K, and X-ray diffraction. At room temperature, the Mössbauer spectrum showed superparamagnetic behavior of the particles, while well-defined sextets were observed at 77K, indicating a blocked regime. The superparamagnetic magnetite nanoparticles can be used as microbead biosensors.

Synthesis and characterisation of CdS nanoparticles in mesoporous copolymer template

Micron-sized spheres of mesoporous styrene-divinylbenzene (Sty-DVB) copolymer were produced by suspension polymerisation in the presence of inert diluents. Using these mesoporous microspheres as a template, optically stable CdS nanoparticles have been synthesized. To characterize these CdS nanoparticles, Raman spectroscopy and micro-photoluminescence were used. We have observed enhanced emission and lasing action at certain wavelengths that correspond to the whispering gallery (WG) modes of the microspheres. High optical stability and low threshold value make this optical system promising in microlaser applications.

Study of magnetic susceptibility of magnetite nanoparticles

In this study dynamic susceptibility (DS) was used to investigate magnetite nanoparticles dispersed in styrene-divinylbenzene copolymer. Transmission electron microscopy (TEM) data have been used to support the DS data analysis. The field dependence of the peak position of the imaginary component of DS was analyzed using a picture of an asymmetric double well potential for the relaxation of the magnetic moment associated with the magnetite nanoparticle. The size dependence of the magnetic susceptibility was included in the data analysis. Nanoparticle-size parameters obtained from the analysis of the DS data (19.1 and 18.2 nm) are in excellent agreement with the values obtained from the fitting of the TEM data (19.2 and 20.1 nm).

Versatile fabrication of paper-based microfluidic devices with high chemical resistance using scholar glue and magnetic masks

Simple methods have been developed for fabricating microfluidic paper-based analytical devices (μPADs) but few of these devices can be used with organic solvents and/or aqueous solutions containing surfactants. This study describes a simple fabrication strategy for μPADs that uses readily available scholar glue to create the hydrophobic flow barriers that are resistant to surfactants and organic solvents. Microfluidic structures were defined by magnetic masks designed with either neodymium magnets or magnetic sheets to define the patter, and structures were created by spraying an aqueous solution of glue on the paper surface. The glue-coated paper was then exposed to UV/Vis light for cross-linking to maximize chemical resistance. Examples of microzone arrays and microfluidic devices are demonstrated. μPADs fabricated with scholar glue retained their barriers when used with surfactants, organic solvents, and strong/weak acids and bases unlike common wax-printed barriers. Paper microzones and microfluidic devices were successfully used for colorimetric assays of clinically relevant analytes commonly detected in urinalysis to demonstrate the low background of the barrier material and generally applicability to sensing. The proposed fabrication method is attractive for both its ability to be used with diverse chemistries and the low cost and simplicity of the materials and process.

The development of a new disposable pipette extraction phase based on polyaniline composites for the determination of levels of antidepressants in plasma samples

In the present work, a new stationary phase for disposable pipette extraction (DPX) based on composites of polyaniline and a styrene-divinylbenzene (SD) copolymer was applied to the analysis of fluoxetine and norfluoxetine in plasma samples using liquid chromatography and fluorescence detector (LC-FD). The DPX variables, such as number of draw/eject cycles, sample pH, type and volume of the desorption solvent, were optimized to established the sorption equilibrium and shorten the analysis time. Among the DPX evaluated variables, the higher extraction efficiency were obtained with 200 μL of plasma mixed with 200 μL of borate solution (pH 9), followed by liquid desorption of the drug with 200 μL acetonitrile in a single cycle. The DPX/LC-FD method demonstrated a linear response over the dynamic range from 10 to 1000 ng mL(-1) for fluoxetine and from 80 ng mL(-1) (LOQ) to 1000 ng mL(-1) for norfluoxetine with r(2)=0.997 and 0.998, respectively. The limit of quantification (LOQ) was 10 ng mL(-1) for fluoxetine and 80 ng mL(-1) for norfluoxetine. Based on the analytical validation results, the proposed method can be a useful tool for determining the fluoxetine and norfluoxetine levels in plasma samples from patients receiving therapeutic dosages.

Magnetic susceptibility investigation of magnetic nanoparticles in styrene-divinylbenzene mesoporous template

In this study, dynamical susceptibility (DS) was used to investigate magnetite-based composites. The field dependence of peaks observed in the DS curves was analyzed within the picture of an asymmetric double well potential for the relaxation of the magnetic moment associated to the magnetite nanoparticle. Parameters obtained from the analysis of the DS data indicate that different magnetite structure, build up from isolated nanoparticles, explains the features observed in the susceptibility curves.

Investigation of magnetic nanoparticles in acrylonitrile-methyl methacrylate-divinylbenzene mesoporous template

Abstract Preparation and characterization of nanosized magnetic particles using alkaline oxidation of ferrous ion retained in acrylonitrile-methyl methacrylate-divinylbenzene (AN-MMA-DVB) spherical micron-sized polymer template is described. Atomic absorption, transmission electron microscopy and magnetic resonance were used to investigate chemically cycled nanoparticle-based composites. The resonance field shifts towards higher values as the nanoparticle concentration reduces in the polymeric template, following two very distinct regimes.

Monitoring the preparation of spherical activated carbon from sulfonated styrene-divinylbenzene copolymer

The production of spherical activated carbons from a sulfonated styrene-divinylbenzene copolymer (Sty/DVB/HSO 3 ) was studied in this work, in order to produce solids for catalytic applications. Differential thermal analysis, termogravimetry, nitrogen adsorption and optical microscopy were used to characterize the samples. It was found that this precursor is suitable to prepare catalyst supports, since the activated spherical carbon showed high thermal stability and high specific surface area, besides micro and mesopores. Supports with different textures, morphologies and chemical structures can be produced by controlling the conditions of polymerization, sulfonation, oxidation, carbonization and activation.