M.F. Da Silva

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.

Biomedical applications of maghemite ferrofluid

The use of cell-targeted ferrofluid in the characterization of modifications of cell membranes is reviewed. Maghemite ferrofluid was synthesized by the Massart method, complexed with dimercaptosuccinic acid (FF). Cell targeting by FF was developed by coupling FF to various biological effectors such as antibodies, lectins, etc, which enabled magnetic cell sorting. Modifications in erythrocyte membranes were studied using FF bound to recombinant human annexin V (AnxFF) which is very sensitive, compared to other Anx-based reagents, in the early detection of phosphatidylserine (PS) exposition on the outer leaflet of the plasma membrane. Thus PS exposition on mouse RBC was detected already after a 24-h storage at 4 degrees C and, transiently, 24 h after their infection by Plasmodium parasites, at which time the parasites are still confined to the liver, thus leading to the recruitment of young RBC and the accumulation of a species, intermediate between reticulocytes and erythrocytes, and the actual RBC target of plasmodial invasion. AnxFF revealed PS exposition on RBC from sickle cell anemia patients, following various inflammations and already after 20 days of human blood storage under blood bank conditions. Such a sensitive detection should be similar to that of macrophages which recognize exposed PS on cells and bring about the latters elimination from the circulation. AnxFF binding determination was combined with that of cell electrophoretic mobility, glycerol resistance and filterability to characterize RBC membrane modifications in Alzheimers disease patients which suggested a continuous damage and regeneration in RBC of these patients. A logistic analysis suggested that several three-parameter combinations could permit diagnosis of Alzheimers disease with up to 95% accuracy. THP1 cells and macrophages, derived themselves by incubation with retinoic acid, were bound to FF and placed in a radio frequency alternating magnetic field. Magnetocytolysis was associated with FF attachment to the cells without damage to non-bound cells and without heating of the surrounding solution.

Biological effects of magnetic fluids: toxicity studies

Toxicity of ionic and citrate-based magnetic fluids administrated intraperitoneally to mice was investigated through cytogenetic analysis, evaluation of mitotic index and morphological and cytometric alterations. Both magnetic fluid samples cause severe inflammatory reactions, being very toxic and thus not biocompatible. Peritoneal cells and tissues studies may provide a useful strategy to investigate the in vivo biological effects of magnetic nanoparticles.

Toxic effects of ionic magnetic fluids in mice

Abstract Toxicity of ionic and tartrate-based magnetic fluids administered intraperitoneally to mice was investigated through morphological and cytometric alterations and cytogenetic analysis. Both magnetic fluids cause cellular death, mutagenicity and severe inflammatory reactions, being very toxic and thus not biocompatible. Peritoneal cell and tissue studies may provide a useful strategy to investigate the in vivo biological effects of magnetic nanoparticles.

A double-coated magnetite-based magnetic fluid evaluation by cytometry and genetic tests

Abstract Magnetite nanoparticles pre-coated with dodecanoic acid and ethoxylated alcohol (DE) were used to obtain a physiologically stable magnetic fluid (DE–MF) sample. Three different doses of DE–MF were intraperitoneally applied to mice. Blood and peritoneum cytometry and micronucleus test were performed for 1–21 days after injection to investigate the DE–MF toxicity. Changes in cell population, peritoneum inflammation, and potential DE–MF genotoxic action were all time and dose dependent. At the lowest dose (5×1015 particles/kg), DE–MF seems to be useful as a drug precursor with both diagnostic and therapeutic values.

Biocompatible magnetic fluids: a comparative birefringence investigation

Abstract The static magnetic birefringence (SMB) of magnetite-based magnetic fluids coated with dextran and dimercaptosuccinic acid was investigated using the recent model proposed by Skeff Neto et al. (J. Appl. Phys. 89 (2001) 3362). The SMB data of samples presenting particle concentration around 1.2×10 16 particle/cm 3 were successfully described. The particle size distribution obtained from the fit of the SMB data was discussed in comparison with the data obtained from transmission electron microscopy.

Birefringence and transmission electron microscopy of monolayer and bilayer magnetoliposomes

In this study, static magnetic birefringence (SMB) and transmission electron microscopy (TEM) were used to investigate magnetite-based monolayer and bilayer magnetoliposomes (MLs). The SMB data were analyzed using the recent model proposed by Skeff Neto et al. (J. Appl. Phys. 89 (2001) 3362). The SMB data indicate that monolayer-based MLs internalize magnetic nanoparticles as dimers while bilayer-based MLs internalize both isolated nanoparticles and dimers. The higher content of dimers inside monolayer MLs has been confirmed by TEM data.