P.C. Morais

Magnetic Resonance of a Dextran-Coated Magnetic Fluid Intravenously Administered in Mice

Magnetic resonance was used to investigate the kinetic disposition of magnetite nanoparticles (9.4 nm core diameter) from the blood circulation after intravenous injection of magnetite-based dextran-coated magnetic fluid in female Swiss mice. In the first 60 min the time-decay of the nanoparticle concentration in the blood circulation follows the one-exponential (one-compartment) model with a half-life of (6.9 +/- 0.7) min. The X-band spectra show a broad single line at g approximately 2, typical of nanomagnetic particles suspended in a nonmagnetic matrix. The resonance field shifts toward higher values as the particle concentration reduces, following two distinct regimes. At the higher concentration regime (above 10(14) cm(-3)) the particle-particle interaction responds for the nonlinear behavior, while at the lower concentration regime (below 10(14) cm(-3)) the particle-particle interaction is ruled out and the system recovers the linearity due to the demagnetizing field effect alone.

The influence of cobalt population on the structural properties of CoxFe3−xO4

CoxFe3−xO4-based (x=0.05–1.6) nanoparticles prepared by combustion reaction were investigated using x-ray diffraction, Raman spectroscopy, and Mossbauer spectroscopy. The Mossbauer data revealed Co2+ in both tetrahedral (site A) and octahedral (site B) sites of the cubic ferrite structure. For x⩽0.4 the experimental data indicated the synthesis of a core-shell structure, with hematite as the shell and cobalt ferrite as the core of the nanoparticle. Differences in crystalline structure between the two phases support the evidences we found of a highly stressed core-shell interface, leading to symmetry reduction of the tetrahedral and octahedral sites.

Effect of the Zn content in the structural and magnetic properties of ZnxMg1−xFe2O4 mixed ferrites monitored by Raman and Mössbauer spectroscopies

Samples of ZnxMg1−xFe2O4 (0≤x≤1) synthesized by the combustion reaction method were investigated by x-ray diffraction, Mossbauer spectroscopy, and Raman spectroscopy. All the samples are found to have a cubic spinel structure and the lattice parameter increases linearly with increasing Zn-content (x). The Mossbauer data showed that the replacement of Mg2+ ions for Zn2+ ions changes substantially the hyperfine parameter. Moreover, it was verified the presence of Fe3+ ions both in A and B sites. The Raman spectra showed five predicted Raman bands for the spinel structure and it was observed the splitting of the A1g Raman mode into tree branches, where each one have been attributed to peaks belonging to each ion (Zn, Mg, and Fe) in the tetrahedral positions.

Synthesis and Characterization of a Magnetic Nanoemulsion as a Promissing Candidate for Cancer Treatment

In this study, we performed the synthesis and characterization of a new class of drug delivery system denominated magnetic nanoemulsion (MNE), which allows the combined action of PDT and HPT therapies, designed to work in a synergic way, leading to an expected enhancement of the tumor damage after minimum doses of heat dissipation and/or visible light photosensitization. The MNPs used in this work are surface-coated with phosphate (PPT) and the photosensitizer used is Zinc phthalocyanine derivative (ZnPC). The morphologic characteristics of MNEs were investigated by transmission electron microscopy. In order to evaluate the entrapment efficiency of PS present on MNEs, we used the UV-vis spectroscopic technique. Photophysical properties of MNE/ZnPC, MNE/PPT and MNE/ZnPC/PPT were studied by time-resolved spectroscopic techniques (triplet lifetimes and singlet oxygen quantum yields). The triplet lifetimes were measured by triplet-triplet absorption flash photolysis.The decay profiles of the MNE/ZnPC and MNE/ZnPC/PPT were measured at 480 nm, under 355 nm Nd-YAG laser excitation.

Magnetic Investigation of CoFe

Magnetic investigation of spinel ferrite nanoparticles dispersed in biocompatible polymeric microspheres is reported in this study. X-ray diffraction data analysis confirms the presence of nanosized CoFe₂O₄ particles (mean size of ~8 nm). This finding is corroborated by transmission electron microscopy micrographs. Magnetization isotherms suggest a spin disorder likely occurring at the nanoparticles surface. The saturation magnetization value is used to estimate particle concentration of 1.6times10¹⁸ cm^-3 dispersed in the polymeric template. A T^1/2 dependence of the coercive field is determined in the low-temperature region (T < 30 K). The model of non-interacting mono-domains is used to estimate an effective magnetic anisotropy of K_eff = 0.6times10⁵ J/m³. The K_eff value we found is lower than the value reported for spherically-shaped CoFe₂O₄ nanoparticles, though consistent with the low coercive field observed in the investigated sample.

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This paper introduces a new class of complex materials that combine the action of photodynamic therapy (PDT) and hyperthermia (HPT) therapies, designed to work in a synergic way, leading to an expected enhancement of the tumor damage after minimum doses of heat dissipation and/or visible light photosensitization . In this study, we evaluated comparative dark and light toxicity of the photosensitisers (PS), biocompatible magnetic fluids(BMF) and BMF/PS complex in the J774-A cell line. Maghemite nanoparticles are surface coated with phosphate (PPT) and chlorine e/sub 6/ (Chle/sub 6/) is used as a PS drug. In the dark toxicity studies, five different concentration of Chle/sub 6/ were evaluated at the lower dark toxicity concentration (5 /spl mu/M). The same studies were developed in the presence of BMFs. No change was observed upon the addition of BMFs. Light toxicity studies were performed with three different fluence of visible light irradiation (2, 5 and 10 J/cm/sup 2/). The methodology used to investigate the cell toxicity in both protocol was the classical MTT assay. All the results presented here allow the development of a new drug generation for cancer treatment extending the possibility of the use of the Chle6/PPT complex as a candidate for maximum tumor damage, acting via photoactivation and/or magnetic field exposure.

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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.

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In this paper, a biocompatible MF sample was investigated using X-band MR. The resonance linewidth broadening (/spl Delta/H/sub R/) and the resonance field (H/sub R/) was investigated as a function of temperature (T), at different nonparticle concentration. The biocompatible MF sample used in this study is based on magnetic nanoparticle (9.4 nm is average diameter) coated with dextran. After precipitation in alkaline medium, magnetite nanoparticles were surface coated to produce stable biocompatible MF samples at physiological pH and salinity.

Nanoparticles Supported in Biocompatible Polymeric Microsphere

We present a systematic study of core-shell Au/Fe3O4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB = 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell.

Evaluation of new complexes of biocompatible magnetic fluid and 3/sup rd/ generation of photosensitizer useful to cancer treatment

Summary form only given. Fe/sub 3/O/sub 4/ nanoparticles obtained by chemical precipitation were treated with two molecular species (dodecanoic acid and a C/sub 12/-C/sub 14/ polyalcohol) to produce three magnetite-coated magnetic fluid (MF) samples. Diluted MF samples (8/spl times/10/sup 15/ particle/cm/sup 3/) were investigated at room temperature using static magnetic birefringence measurements (SMB). The mean particle diameter (8.9 /spl plusmn/ 0.2 nm) and the diameter dispersity (0.31 /spl plusmn/ 0.01) obtained from the fitting of the SMB data were in excellent agreement with the data obtained from transmission electron microscopy (9.4 /spl plusmn/ 0.1 nm and 0.32 /spl plusmn/ 0.01). Such agreement could only be achieved by considering the field dependence of the magnetic permeability and dimer formation. The dimer magnetic permeability depends upon the nanoparticle coating, thus suggesting particle-particle interaction effects . The dimer magnetic permeability coating layer thickness dependence is examined.