8TH INTERNATIONAL CONFERENCE ON THE SCIENTIFIC AND CLINICAL APPLICATIONS OF MAGNETIC CARRIERS
1311(2010); http://dx.doi.org/10.1063/1.3530045View Description Hide Description
Aniline surface coated nanoparticles have been successfully synthesized by UV irradiation varying the time and the acid media (HCl, or The synthesized material represents a promising platform for application in nerve regeneration. XRD patterns are consistent with the crystalline structure of magnetite. Nevertheless, for UV irradiation times longer than 2 h, extra XRD lines reveal the presence of goethite. The mean crystallite size of uncoated particles is estimated to be 25.4 nm, meanwhile that size is reduced to 19.9 nm for the UV irradiated sample in HCl medium for 4 h. Mössbauer spectra of uncoated nanoparticles reveal the occurrence of thermal relaxation at room temperature, while the 77 K‐Mössbauer spectrum suggests the occurrence of electron localization effects similar to that expected in bulk magnetite. The Mossbauer spectra of UV irradiated sample in HCl medium during 4 h, confirms the presence of the goethite phase. For this sample, the thermal relaxation is more evident, since the room temperature spectrum shows larger spectral area for the nonmagnetic component due to the smaller crystallite size. Meanwhile, the 77 K‐Mössbauer spectrum suggests the absence of the electron localization effect above 77 K.
Elegant Synthesis Strategies Using a New Magnetic Bed Reactor: Monoclonal Mouse anti‐CD11b Derivatized Superparamagnetic Iron Oxide Nanoparticles1311(2010); http://dx.doi.org/10.1063/1.3530066View Description Hide Description
The new magnetic reactor based solid phase synthesis strategy allows magnetic immobilization of nanoparticles in order to perform the derivatization step(s) with relevant biomolecules on the immobilized magnetic nanoparticles. Monoclonal Mouse anti‐Human CD11b shows affinity toward monocyte/macrophage integrin MAC‐1 (CD11b/CD18) which is involved in leukocyte adhesion and functions as a cell receptor and was coupled on superparamagnetic iron oxide nanoparticles (SPIONs) in this reactor. The resulting anti‐CD11b derivatized SPIONs were analyzed and compared to conventionally derivatized SPIONs. The reactor‐derivatized anti‐CD11b‐SPIONs show enhanced colloidal stability during and after the surface derivatization steps. The yield and quality of the resulting particles can also be significantly improved in terms of reaction time and yield, particle size distribution, and scalability by using this magnetic reactor. These highly specific particles were successfully used in imaging studies of monocytes.
1311(2010); http://dx.doi.org/10.1063/1.3530006View Description Hide Description
Magnetic optical sensor particles (MOSePs) in nanometer scale for pH measurement were synthesized and characterized. The measurement of pH is based on a ratiometric evaluation of the fluorescence of a pH‐sensitive indicator dye (N‐fluorescein‐acrylamide) and a reference dye (a rhodamine derivative) which is not affected by pH. Measurement of pH in aqueous media in the range of pH 5 to 9 is reversibly possible. As the particles can be collected in front of fiber optics with a specially designed separator, signal enhancement is easily achieved. Therefore, a low concentration of MOSePs is sufficient for investigations. Using the here reported MOSePs, the read out of pH is noninvasive, i.e., no dip probe needs to be inserted into the medium. In addition, no further preparation steps are required, pH‐sensitive MOSePs can be simply pipetted into the medium prior to measurement, magnetically collected at the side and read out with a fiber optic device through the glass wall.
1311(2010); http://dx.doi.org/10.1063/1.3530014View Description Hide Description
We report a comparative study of hybrid nanostructures prepared by using water based magnetic nanofluids and polymers such as poly(N‐isopropylacrylamide) and pyrrole copolymer functionalized with glycyl‐leucine. Design of magnetic nanostructures could be achieved using different synthesis procedures that allow either coating or clustering the magnetic nanoparticles from magnetic fluid by the addition of polymer. Physical‐chemical characteristics of hybrid magnetic nanostructures were investigated by FTIR, TEM, DLS, rotational viscosimetry and magnetization measurements. Functionalized pyrrole copolymer coated magnetite nanoparticles with mean size around 9 nm have superparamagnetic behavior and saturation magnetization value of Clusters of magnetite nanoparticles from the water based magnetic nanofluid were encapsulated into polymeric PNIPA spheres having diameters in the range 50–100 nm. The procedure applied allowed to achieve high magnetic loading of polymeric microspheres, having saturation magnetization value of 41 emu/g. Also, the stable suspension in water of thermoresponsive magnetic microgel, as well as the dried samples shows superparamagnetic behavior. It was evidenced that the thermally induced transition from the swollen to collapsed state of magnetic microgels occurs around 30° C.
Synthesis, Characterization, and Preliminary Investigation of Cell Interaction of Magnetic Nanoparticles with Catechol‐Containing Shells1311(2010); http://dx.doi.org/10.1063/1.3530028View Description Hide Description
Superparamagnetic iron oxide cores were synthesized by co‐precipitation of Fe(II) and Fe(III) salts and subsequently stabilized by coating with different catechols (levodopa, dopamine, hydrocaffeic acid, dopamine‐containing carboxymethyl dextran) known to act as high‐affinity, bidentate ligands for Fe(III). The prepared stable magnetic fluids were characterized with regard to their chemical composition (content of iron and shell material, Fe(II)/Fe(III) ratio) and their physical properties (size, surface charge, magnetic parameters). The nanoparticles showed no or only slight cytotoxic effects within 1 and 4 days of incubation with 3T3 fibroblast cells. Preliminary experiments were performed to study the interaction of the prepared nanoparticles with human MCF‐7 breast cancer cells and leukocytes. An intense interaction of the MCF‐7 cells with these particles was found whereas the leukocytes showed a lower tendency of interaction. Based on these finding, the novel magnetic nanoparticles possess the potential for use in depletion of tumor cells from peripheral blood.
1311(2010); http://dx.doi.org/10.1063/1.3530041View Description Hide Description
In this study the design and set up of a very sensitive RF susceptometer based on a Robinson NMR oscillator is presented. This home‐made susceptometer operates in a frequency range of 10–40 MHz and was successfully used to study thermal relaxation and particle interaction in magnetic nanoparticulated systems. Using this system we found the peak frequency associated to the energy absorption by the magnetite‐based nanoparticulated material changing in the range of 17 to 28 MHz by applying a DC magnetic field up to 4 kOe.
Determination of Nanocrystal Size Distribution in Magnetic Multicore Particles Including Dipole‐Dipole Interactions and Magnetic Anisotropy: a Monte Carlo Study1311(2010); http://dx.doi.org/10.1063/1.3530051View Description Hide Description
A correct estimate of the size distribution (i.e., median diameter D and geometric standard deviation σ) of the magnetic nanocrystals (MNCs) embedded in magnetic multicore particles is a necessity in most applications relying on the magnetic response of these particles. In this paper we use a Monte Carlo method to simulate the equilibrium magnetization of two types of multicore particles: (I) MNCs fused in a random compact cluster, and (II) MNCs distributed on the surface of a large carrier sphere. The simulated magnetization data are then fitted using a common method based on a Langevin equation weighted with a size distribution function. Finally, the fitting parameters and are compared to the real parameters and used to generate the MNCs. Our results show that fitting magnetization data with a Langevin model that neglects magnetic anisotropy and dipole‐dipole interactions leads to an erroneous estimate of the size distribution of the MNCs in multicore particles. The magnitude of the error depends on the particle morphology, number of MNCs contained in the particle and magnetic properties of the MNCs.
Characterization of Dispersion Properties of Magnetic Fluids by Multisample Analytical Centrifugation1311(2010); http://dx.doi.org/10.1063/1.3530060View Description Hide Description
Carefully designed colloidal properties are the prerequisite for successful diagnostic and therapeutic applications of magnetic fluids (MF). A high degree of dispersion (small particle size, absence of agglomeration) and stability is required. Multisample analytical centrifugation with high resolution photometric detection was applied to characterize the quality of a range of differently stabilized MF’s.
Comparison of the ‘fingerprints’ gives a fast overview over differences in MF quality (quality of particle stabilization against aggregation, separation stability).
Sedimentation kinetics and the distribution of sedimentation velocity allow for a more detailed quantitative comparison and ranking between different products and batches. Even without any material properties well dispersed samples with narrow distribution can be discriminated from samples with broader distribution and oversized particles (agglomeration).
1311(2010); http://dx.doi.org/10.1063/1.3530061View Description Hide Description
We examined magnetization states of agglomerates for two types of nanoparticle agglomerate systems, where primary crystallites have either blocked magnetization or are superparamagnetic at room temperature. We determined the magnetization state of the agglomerates with measuring magnetic permeability as a function of frequency and measuring magnetization as a function of temperature for zero‐field cooled and field‐cooled samples. Then we examined specifically the magnetization state of agglomerates made from blocked crystallites and we used magnetic flux measurements at different magnetic conditions. Our results show that in the case of superparamagnetic behavior of individual crystallites also the agglomerate can retain superparamagnetic behavior, whereas for crystallites with blocked magnetization nonuniform magnetization state of the agglomerate is possible.
1311(2010); http://dx.doi.org/10.1063/1.3530062View Description Hide Description
In this work, we show how one can convert the energy barrier distribution over temperature, which is the result of temperature dependent magnetorelaxometry, to a distribution of the size of the magnetically active cores of fractioned magnetic solutions by using additional susceptometric measurements.
1311(2010); http://dx.doi.org/10.1063/1.3530063View Description Hide Description
A ferrofluid based on has been synthesized using the condensation method by coprecipitating aqueous solutions of and mixtures in and treated further in order to obtain colloidal sols by creating a charge density on their surface and functionalized by carapa guianensis (andiroba oil). Aqueous sample with an average particle diameter ∼7 nm were studied by Mössbauer spectroscopy and dc magnetization measurements in the range of 4.2–250 K. The saturation magnetization at 4.2 K was determined from M vs 1/H plots by extrapolating the value of magnetizations to infinite fields, to 5.6 emu/g and coercivity to 344 Oe. The low saturation magnetization value was attributed to spin noncollinearity predominantly at the surface. From the magnetization measurements a magnetic anisotropy energy constant (K) of was calculated. spectra at room temperature showed a singlet due to superparamagnetic relaxation and a sextet at low temperature.
1311(2010); http://dx.doi.org/10.1063/1.3530064View Description Hide Description
Magnetic fields can be used to direct magnetically susceptible nanoparticles to disease locations: to infections, blood clots, or tumors. Any single magnet always attracts (pulls) ferro‐ or para‐magnetic particles towards it. External magnets have been used to pull therapeutics into tumors near the skin in animals and human clinical trials. Implanting magnetic materials into patients (a feasible approach in some cases) has been envisioned as a means of reaching deeper targets. Yet there are a number of clinical needs, ranging from treatments of the inner ear, to antibiotic‐resistant skin infections and cardiac arrhythmias, which would benefit from an ability to magnetically “inject”, or push in, nanomedicines. We develop, analyze, and experimentally demonstrate a novel, simple, and effective arrangement of just two permanent magnets that can magnetically push particles. Such a system might treat diseases of the inner ear; diseases which intravenously injected or orally administered treatments cannot reach due to the blood‐brain barrier.
1311(2010); http://dx.doi.org/10.1063/1.3530065View Description Hide Description
Nanosized magnetite particles, with mean physical diameter of about 7 nm, obtained by chemical coprecipitation procedure were dispersed in water carrier by applying sterical stabilization of particles in order to prevent their aggregation and to ensure colloidal stability of the systems. Different chain length (C12, C14, C18) carboxylic acids (lauric (LA), myristic (MA) and oleic (OA)) were used for double layer coating of magnetite nanoparticles. Structural and magnetic properties were investigated by electron microscopy (TEM), dynamical and static light scattering (DLS, SLS) and magnetometry (VSM) to evaluate the role of chain length and of the saturated/unsaturated nature of surfactant layers. Also investigated were two water based magnetic nanocomposites obtained by encapsulating the magnetic nanoparticles in polymers with different functional properties.
Estimation of the Oblongness of Aggregates of Magnetic Particles Formed in Static Magnetic Field Using ESR Spectroscopy1311(2010); http://dx.doi.org/10.1063/1.3530067View Description Hide Description
Aggregation process in magnetic fluid has been investigated by electron spin resonance method. A low molecular paramagnet (paramagnetic sensor) has been added to magnetite hydrosol and its ESR spectra have been analyzed. Fraction of aggregated particles and aggregate oblongness have been calculated using new theoretical model for the ESR spectra of paramagnetic sensor in diluted magnetic media containing elongated structures.
1311(2010); http://dx.doi.org/10.1063/1.3529998View Description Hide Description
This study investigated the nonlinear behavior of magnetic fluids under high excitation fields due to nonlinear Brownian relaxation. As a direct indication of nonlinear behavior, we characterized the higher harmonics of the magnetization signal generated by the magnetic fluid. The amplitudes of the fundamental to the ninth harmonic of the magnetization signal were measured as a function of the external field. The experimental results were compared with numerical simulations based on the Fokker‐Planck equation, which describes nonlinear Brownian relaxation. To allow a quantitative comparison, we estimated the size distribution and size dependence of the magnetic moment in the sample. In the present magnetic fluid, composed of agglomerates of particles, the magnetic moment was estimated to be roughly proportional to the diameter of the particles, in contrast to the case of single‐domain particles. When the size distribution and the size dependence of the magnetic moment were taken into account, there was good quantitative agreement between the experiment and simulation.
1311(2010); http://dx.doi.org/10.1063/1.3529999View Description Hide Description
Magnetic microsphere suspensions undergo complex motion when exposed to finite sources of the magnetic field, such as small permanent magnets. The computational complexity is compounded by a difficulty in choosing a suitable choice of visualization tools because this often requires using the magnetic force vector field in three dimensions. Here we present a potentially simpler approach by using the magnetic pressure. It is a scalar quantity, and its usefulness has been already demonstrated in applications to magnetohydrodynamics and ferrohydrodynamics (where B is the applied field and The equilibrium distribution of the magnetic bead plug in aqueous suspension is calculated as an isosurface of the magnitude of the magnetic pressure in the field of two permanent magnet blocks calculated from closed formulas. The geometry was adapted from a publication on the magnetic bead suspensions in microsystems and the predicted bead plug distribution is shown to agree remarkably well with the experiment.
Contribution to the Study of Ferrite Nanobeads: Synthesis, Characterization and Investigation of Horizontal Low Gradient Magnetophoresis Behaviour1311(2010); http://dx.doi.org/10.1063/1.3530000View Description Hide Description
In this work we investigate the possibilities of the use of Horizontal Low Gradient Magnetic Field (HLGMF) (<100 T/m) for filtration, control and separation of the synthesized magnetic particles, considering, the characteristics of the suspension, the size and the type of nanoparticles (NPs) and focusing on the process scale up. Reversible aggregation is considered in the different steps of magnetic nanobeads synthesis. For these purpose, we synthesized ‐silica core‐shell nanobeads by co‐precipitation, monodispersion and silica coating. SQUID, TEM, XRD, and Zeta potential techniques were used to characterize the synthesized nanobeads. An extensive magnetophoresis study was performed at different magnetophoretic conditions. Different reversible aggregation times were observed at different HLGMF, at each step of the synthesis route: Several orders of magnitude differences where observed when comparing citric acid (CA) suspension with silicon coated beads. Reversible aggregation times are correlated with the properties of the NPs at different steps of synthesis.
Immobilization of Thiadiazole Derivatives on Magnetite Mesoporous Silica Shell Nanoparticles in Application to Heavy Metal Removal from Biological Samples1311(2010); http://dx.doi.org/10.1063/1.3530001View Description Hide Description
In this report magnetite was synthesized by a coprecipitation method, then coated with a layer of silica. Another layer of mesoporous silica was added by a sol‐gel method, then 5‐amino‐1,3,4‐thiadiazole‐thiol (ATT) was immobilized onto the synthesized nanoparticles with a simple procedure. This was followed by a series of characterizations, including transmission electron microscopy (TEM), FT‐IR spectrum, elemental analysis and XRD. Heavy metal uptake of the modified nanoparticles was examined by atomic absorption spectroscopy. For further investigation we chose as the preferred heavy metal to evaluate the amount of adsorption, as well as the kinetics and mechanism of adsorption. Finally, the capacity of our nanoparticles for the heavy metal removal from blood was shown. We found that the kinetic rate of adsorption was 0.05 g/mg/min, and the best binding model was the Freundlich isotherm.
Manufacture and Testing of a High Field Gradient Magnetic Fractionation System for Quantitative Detection of Plasmodium falciparum Gametocytes1311(2010); http://dx.doi.org/10.1063/1.3530002View Description Hide Description
Plasmodium falciparum is the most dangerous of the human malaria parasite species and accounts for millions of clinical episodes of malaria each year in tropical countries. The pathogenicity of Plasmodium falciparum is a result of its ability to infect erythrocytes where it multiplies asexually over 48 h or develops into sexual forms known as gametocytes. If sufficient male and female gametocytes are taken up by a mosquito vector, it becomes infectious. Therefore, the presence and density of gametocytes in human blood is an important indicator of human‐to‐mosquito transmission of malaria. Recently, we have shown that high field gradient magnetic fractionation improves gametocyte detection in human blood samples. Here we present two important new developments. Firstly we introduce a quantitative approach to replace the previous qualitative method and, secondly, we describe a novel method that enables cost‐effective production of the magnetic fractionation equipment required to carry out gametocyte quantification. We show that our custom‐made magnetic fractionation equipment can deliver results with similar sensitivity and convenience but for a small fraction of the cost.