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Magnetic nanoparticles are excellent contrast agents for imaging within the body because they provide a signal that can be detected through tissue. This chapter reviews magnetic nanoparticles and imaging techniques. It focuses on magnetic resonance imaging (MRI), but also briefly describes magnetomotive optical coherence tomography, magnetic particle imaging (MPI), and magnetomotive ultrasound.

Poly(N-isopropylacrylamide) (PNIPAM), which undergoes a temperature dependent transition from hydrophilic to hydrophobic, has played a crucial role in the development of stimuli-responsive multifunctional nanoparticles. In particular, iron oxide nanoparticles coated with PNIPAM have been effectively developed to enable stimuli responsive drug delivery and imaging agents. However, the PNIPAM transition from hydrophilic to hydrophobic at physiologically relevant temperatures renders colloidal nanoparticles unstable resulting in aggregation and precipitation from solution. Consequently, a direct correlative analysis of the effect of the thermally induced phase transition of PNIPAM on the magnetic resonance properties of nanoparticles has not been possible as the changes in proton relaxivity have been dominated by the colloidal agglomeration of the nanoparticles. Herein, we report colloidally stable thermoresponsive PNIPAM-grafted-PGMA coated magnetite core/shell nanoparticles (PNIPAM–PGMA–NPs) that enable the direct analysis of the effect of PNIPAM phase changes in solution on the overall magnetic resonance relaxivity of nanoparticles in suspension.

We report on cerium substituted bismuth dysprosium iron garnet of composition Bi 1.3 Ce 0.3 Dy 1 Fe 5 O 12 prepared by biased target ion beam deposition on a fused quartz substrate and postdeposition crystallization through rapid thermal annealing in air. The resulting thin film garnet achieved promising magnetic and magneto-optic (MO) properties on a low cost amorphous substrate and with reduced thermal budget toward potential MO applications and semiconductor processing for films of similar composition.

We present a first study of a long-term phantom for Magnetic Resonance Imaging (MRI) and X-ray imaging of biological tissues with magnetic nanocomposites (MNC) suitable for 3-dimensional and quantitative imaging of tissues after, e.g. magnetically assisted cancer treatments. We performed a cross-calibration of X-ray microcomputed tomography (XµCT) and MRI with a joint calibration standard for both imaging techniques. For this, we have designed a phantom for MRI and X-ray computed tomography which represents biological tissue enriched with MNC. The developed phantoms consist of an elastomer with different concentrations of multi-core MNC. The matrix material is a synthetic thermoplastic gel, PermaGel (PG). The developed phantoms have been analyzed with Nuclear Magnetic Resonance (NMR) Relaxometry (Bruker minispec mq 60) at 1.4 T to obtain R2 transverse relaxation rates, with SQUID (Superconducting QUantum Interference Device) magnetometry and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to verify the magnetite concentration, and with XµCT and 9.4 T MRI to visualize the phantoms 3-dimensionally and also to obtain T2 relaxation times. A specification of a sensitivity range is determined for standard imaging techniques X-ray computed tomography (XCT) and MRI as well as with NMR. These novel phantoms show a long-term stability over several months up to years. It was possible to suspend a particular MNC within the PG reaching a concentration range from 0 mg/ml to 6.914 mg/ml. The R2 relaxation rates from 1.4 T NMR-relaxometry show a clear connection ( R 2 =0.994) with MNC concentrations between 0 mg/ml and 4.5 mg/ml. The MRI experiments have shown a linear correlation of R2 relaxation and MNC concentrations as well but in a range between MNC concentrations of 0 mg/ml and 1.435 mg/ml. It could be shown that XµCT displays best moderate and high MNC concentrations. The sensitivity range for this particular XµCT apparatus yields from 0.569 mg/ml to 6.914 mg/ml. The cross-calibration has defined a shared sensitivity range of XµCT, 1.4 T NMR relaxometer minispec, and 9.4 T MRI. The shared sensitivity range for the measuring method (NMR relaxometry) and the imaging modalities (XµCT and MRI) is from 0.569 mg/ml, limited by XµCT, and 1.435 mg/ml, limited by MRI. The presented phantoms have been found to be suitable to act as a body tissue substitute for XCT imaging as well as an acceptable T2 phantom of biological tissue enriched with magnetic nanoparticles for MRI.

Epsilon cobalt (ε-Co) nanoparticles in a number of octahedral morphologies have been synthesised. The particles are polycrystalline, with sizes in the order of 30 nm. Magnetic studies reveal the particles are ferromagnetic, with a room temperature saturation magnetisation of 131 emu g(-1). Unlike other large cubic ε-Co syntheses, we have not added an additional co-surfactant. Instead, we have modified the heating regime and reaction agitation. This alternative method highlights the complex chemistry associated with the formation of cobalt nanoparticles by thermal decomposition.

It is demonstrated for the first time that amorphous bismuth iron garnet films can be crystallized within capacitively coupled oxygen plasmas at temperatures approximately 100 °C lower than required using conventional thermal annealing. We characterize the plasma optical emissions at high pressures (2 Torr–5 Torr) and high rf powers (500 W–800 W) and show that film crystallization is nevertheless related to thermal conditions generated in the plasma. It is demonstrated that these thermal conditions are related to the concentration of the dominant oxygen species O and O+ in the plasma, which, in turn, are a function of the rf power and pressure. The plasma treated garnet Faraday rotation and optical transmission are shown to be comparable with conventional oven or rapid thermal annealing.It is demonstrated for the first time that amorphous bismuth iron garnet films can be crystallized within capacitively coupled oxygen plasmas at temperatures approximately 100 °C lower than required using conventional thermal annealing. We characterize the plasma optical emissions at high pressures (2 Torr–5 Torr) and high rf powers (500 W–800 W) and show that film crystallization is nevertheless related to thermal conditions generated in the plasma. It is demonstrated that these thermal conditions are related to the concentration of the dominant oxygen species O and O+ in the plasma, which, in turn, are a function of the rf power and pressure. The plasma treated garnet Faraday rotation and optical transmission are shown to be comparable with conventional oven or rapid thermal annealing.

Here, we present the magnetic properties of silica-coated magnetite nanoparticles. We have coated 7 nm of Fe3O4 with cetyltrimethylammonium bromide (CTAB) for phase transformation from hydrophobic to hydrophilic. Core-shell structure of silica-coated magnetite nanoparticles have been obtained using surfactant templated sol-gel method. The obtained silica-coated magnetite nanoparticles were characterized by transmission electron microscopy (TEM), fourier transform infrared (FTIR) spectroscopy and superconducting quantum interference device (SQuID). The hysteresis loops of the coated particles were measured using SQuID and the results showed a superparamagnetic behavior at room temperature. The saturation magnetization (Ms) of the coated particles indicate the presence of non-magnetic surface layers resulting from the strong chemical attachment of the silica to the Fe3O4’s surface, also observed by FTIR spectroscopy.

We report on the deposition, crystallization, and magnetic properties of cerium-substituted europium iron garnet having the general form of (CeEu)3(FeGa)5O12. The films were deposited on gallium gadolinium garnet and fused quartz substrates using biased target ion beam deposition at a rate of 2.7 nm/min. The Ce:EIG thin film has a composition of Ce1.3Eu1.7Fe3Ga1.6O12, with 30% of the Ce in the 4+ oxidation state and the remainder as Ce 3+ . The film exhibits the primary peaks of the garnet phase in X-ray diffraction patterns. In the visible part of the electromagnetic spectrum, the film on GGG exhibits a Faraday rotation of 3.3°/µm with coercivity of 0.58 kOe, whereas the film on fused quartz exhibits 1.1°/µm with a coercivity of 0.8 kOe. The film on the fused quartz substrate has a saturation magnetization of 17 emu/cm 3 at room temperature.

We report the fabrication of magnetic particles comprised of clusters of iron oxide nanoparticles, 7.4 nm mean diameter, stabilized by a biocompatible, amphiphilic diblock copolymer, poly(ethylene oxide-b-d,l-lactide). Particles with quantitative incorporation of up to 40 wt % iron oxide and hydrodynamic sizes in the range of 80–170 nm were prepared. The particles consist of hydrophobically modified iron oxide nanoparticles within the core-forming polylactide block with the poly(ethylene oxide) forming a corona to afford aqueous dispersibility. The transverse relaxivities (r2) increased with average particle size and exceeded 200 s–1 mM Fe–1 at 1.4 T and 37 °C for iron oxide loadings above 30 wt %. These experimental relaxivities typically agreed to within 15% with the values predicted using analytical models of transverse relaxivity and cluster (particle core) size distributions derived from cryo-TEM measurements. Our results show that the theoretical models can be used for the rational design of biocomp...

We report the synthesis, characterisation and evaluation of the in vitro biocompatibility of polymeric nanoparticles with both magnetic and upconverting fluorescent properties. The particles consist of superparamagnetic iron oxide nanoparticles and upconverting NaYF4:Yb,Er nanoparticles co-encapsulated within a poly(glycidyl methacrylate) sphere. Two different upconverting nanoparticles (10 nm α-NaYF4:Yb,Er and 50 nm β-NaYF4:Yb,Er) were synthesised and the optical and magnetic properties of the composite polymeric nanoparticle systems assessed by near infra-red laser spectroscopy, SQUID magnetometry and proton relaxometry. A live-dead assay was used to assess the viability of PC-12 neural cells incubated with varying concentrations of the nanoparticles. The composite nanoparticles produced no observed impact on cellular viability even at concentrations as high as 1000 μg mL−1. Confocal microscopy revealed uptake of nanoparticles by PC-12 cells and peri-nuclear cytoplasmic localisation. Both particle systems show favourable magnetic properties. However, only the nanospheres containing 50 nm β-NaYF4:Yb,Er were suitable for optical tracking because the presence of iron oxide within the composites imparts a significant quenching of the upconversion emission. This study demonstrates the size and phase of the upconverting nanoparticles are important parameters that have to be taken into account in the design of multimodal nanoparticles using co-encapsulation strategies.

We report on the preparation and characterization of crystalline bismuth oxide thin films via Biased Target Ion Beam Deposition method. A focused blue laser (405nm) is used to write an array of dots in the bismuth oxide thin film and demonstrate clear and circular recording marks in form of “bubbles” or “little volcanos” (FWHM ∼500nm). Results indicate excellent static recording characteristics, writing sensitivity and contrast. The recording mechanism is investigated and is believed to be related to laser-induced morphology change.

BACKGROUND AND OBJECTIVE: Particulate matter

Purpose The process of invasion and metastasis formation of tumor cells can be studied by following the migration of labeled cells over prolonged time periods. This report investigates the applicability of iron oxide nanoparticles as a magnetic resonance imaging (MRI) contrast agent for cell labeling. Methods γFe2O3 nanoparticles prepared with direct flame spray pyrolysis are biofunctionalized with poly-l-lysine (PLL). The nanoparticles within the cells were observed with transmission electron microscopy, bright-field microscopy, and magnetorelaxometry. MRI of labeled cells suspended in agarose was used to estimate the detection limit. Results PLL-coated particles are readily taken up, stored in intracellular clusters, and gradually degraded by the cells. During cell division, the nanoparticle clusters are divided and split between daughter cells. The MRI detection limit was found to be 25 cells/mm3 for R2*, and 70 cells/mm3 for R2. The iron specificity, however, was higher for R2 images. Due to the degradation of intracellular γFe2O3 to paramagnetic iron ions within 13 days, the R1, R2, and R2* contrast gradually decreased over this time period to approximately 50% of its initial value. Conclusions These results suggest that PLL-coated γFe2O3 nanoparticles can be used as an MRI contrast agent for long-term studies of cell migration. Magn Reson Med 71:1896–1905, 2014. © 2013 Wiley Periodicals, Inc.

Human red blood cells were loaded with gadoteric acid by two different methods. The methods comprised either hypo-osmolar incubation or a hypo-osmolar pulse in the presence of gadoteric acid. The resulting enhancements in proton relaxivities of cell suspensions in 1.4 T were measured and the effect of incubation osmolarity on the resulting proton relaxivity was also studied. The osmotic pulse method was found to yield the greatest cell-specific relaxivity enhancements (71-fold for longitudinal relaxivity and 39-fold for transverse relaxivity). The spatial distribution of the gadolinium within the cells was studied using energy filtered transmission electron microscopy to generate gadolinium M-edge jump ratio images. All surviving cells exposed to gadoteric acid under hypo-osmolar conditions showed enhanced (relative to control cells) and generally uniform intensity within the cells in gadolinium jump ratio images suggesting all cells are susceptible to loading and that the loading is generally spatially uniform within each cell. There was some evidence for a small amount precipitation or aggregation of gadolinium within some cells prepared by the hypo-osmolar incubation method.

Biosensing with ferromagnet-based magnetoresistive devices has been dominated by electrical detection of particle-induced changes to the devices' static magnetic configuration. There are however potential advantages to be gained from using field dependent, high frequency magnetization dynamics for magnetic particle detection. Here we demonstrate the use of nano-confined ferromagnetic resonances in periodically patterned magnetic films for the detection of adsorbed magnetic particles with diameters ranging from 6 nm to 4 $\mu$m. The nanopatterned films contain arrays of holes which can act as preferential adsorption sites for small particles. Hole-localized particles act in unison to shift the resonant frequencies of the various modes of the patterned layer with shift polarities determined by the localization of each mode within the nanopattern's repeating unit cell. The same polarity shifts are observed for a large range of coverages, even when hole-localized particles are covered by quasi-continuous particle sheets. For large particles however, preferential adsorption no longer occurs, leading to resonance shifts with polarities which are independent of the mode localization. Analogous shifts are seen in continuous layers where, for small particles, the shift of the layer's fundamental mode is typically about 10 times less than in patterned systems and induced by relatively weak fields emanating beyond the particle in the direction of the static applied field. This highlights the importance of having confined modes consistently positioned with respect to nearby particles., Comment: 31 pages, 15 figures

Synthetic multifunctional electrospun composites are a new class of hybrid materials with many potential applications. However, the lack of an efficient, reactive large-area substrate has been one of the major limitations in the development of these materials as advanced functional platforms. Herein, we demonstrate the utility of electrospun poly(glycidyl methacrylate) films as a highly versatile platform for the development of functional nanostructured materials anchored to a surface. The utility of this platform as a reactive substrate is demonstrated by grafting poly(N-isopropylacrylamide) to incorporate stimuli–responsive properties. Additionally, we demonstrate that functional nanocomposites can be fabricated using this platform with properties for sensing, fluorescence imaging, and magneto-responsiveness.

The preparation of discrete tetranuclear lanthanide/alkali metal (Ae) assemblies bearing a tribenzoylmethane ligand (LH) is discussed. These assemblies have the general formula [Ln(Ae·HOEt)(L)4]2, where Ln3+ = Gd3+, Tb3+, Dy3+, Ho3+ and Ae+ = Na+, K+, Rb+. The coordination geometries of the lanthanide species were analyzed and compared, revealing a trend between an eight-coordinate square antiprism and triangular dodecahedron dependent on the nature of lanthanide, alkali metal, and lattice solvent. The potassium-containing analogs were also analyzed for their magnetic susceptibility.

Surface modification with linear polymethacrylic acid (20 kDa), linear and branched polyethylenimine (25 kDa), and branched oligoethylenimine (800 Da) is commonly used to improve the function of magnetite nanoparticles (MNPs) in many biomedical applications. These polymers were shown herein to have different adsorption capacity and anticipated conformations on the surface of MNPs due to differences in their functional groups, architectures, and molecular weight. This in turn affects the interaction of MNPs surfaces with biological serum proteins (fetal bovine serum). MNPs coated with 25 kDa branched polyethylenimine were found to attract the highest amount of serum protein while MNPs coated with 20 kDa linear polymethacrylic acid adsorbed the least. The type and amount of protein adsorbed, and the surface conformation of the polymer was shown to affect the size stability of the MNPs in a model biological media (RPMI-1640). A moderate reduction in r 2 relaxivity was also observed for MNPs suspended in RPMI-1640 containing serum protein compared to the same particles suspended in water. However, the relaxivities following protein adsorption are still relatively high making the use of these polymer-coated MNPs as Magnetic Resonance Imaging (MRI) contrast agents feasible. This work shows that through judicious selection of functionalization polymers and elucidation of the factors governing the stabilization mechanism, the design of nanoparticles for applications in biologically relevant conditions can be improved. © 2012 American Chemical Society., ARC (DP0985848); Spanish ISCIII-MSPS (CD09/00030)

Magnetic nanoparticles coated with polymers have existing and further potential for applications in medicine, including magnetic resonance imaging (MRI) imaging for diagnostics and assessing biodistribution, and their capacity to remotely generate heat in response to alternating current magnetic fields to elicit biological responses. Advances in such domains rely on developing better understanding of how such materials respond to magnetic fields. This paper reports thermosensitive properties of poly(N-isopropylacrylamide-co-Nile Red)-coated magnetic nanostructures upon passing through the lower critical solution temperature (LCST) of the polymer brush, and correlation of this behavior with formation of aggregates. Discrete magnetite nanoparticles coated with brush layers comprised of terminally attached poly(N-isopropylacrylamide-co-Nile Red) afforded highly water-dispersible nanoparticles (intensity average diameter of 38 nm) with good colloidal stability in phosphate buffers. The nanoparticles displayed...

This study investigated the metallurgical origin of the effects of Fe substitution for Mn on the martensitic and the magnetic transformation behaviours of Ni50Mn40-xSn10Fex (x = 0, 3, 4, 5, 6) alloys. Substitution of Fe for Mn at above 3 at% introduced an fcc gamma phase in the microstructure. Formation of the gamma phase influenced the composition of the bcc/B2 matrix, leading to decrease in martensitic transformation temperatures and transformation entropy change. The Curie temperature of the parent phase increased slightly, whereas the Curie temperature of the martensite increased rapidly with increasing Fe addition. Changes in the temperatures of the martensitic and magnetic transformations are confirmed to directly relate to the eta ratio of the matrix caused by formation of gamma phase. The minimum eta ratio value for the occurrence of the martensitic transformation is estimated to be 8.045 for the alloy system studied. A narrow e/a ratio range of 8.113-8.137 is estimated for the occurrence of metamagnetic transformationM(para) double left right arrow A(ferro). This metamagnetic reverse transformation was induced by a magnetic field at 225 K within a range of 3-7 Tin the Ni50Mn35Sn10Fe5 alloy. The magnetic work required to induce the transformation is estimated to be similar to 176 J/kg, comparable to the thermodynamic energy deficit for the transformation at the testing temperature estimated from thermal measurement. These findings clarify the origin of the effects of Fe doping in Ni50Mn40-xSm10 alloys and provides reference on alloys design for this system. (C) 2010 Elsevier Ltd. All rights reserved.

Polymer–magnetite nanoparticle complexes that respond to both magnetic fields and to temperature have been demonstrated. Novel alkyl halide-functional bis(diethylphosphonate) esters were prepared and utilized as initiators for polymerizing N-isopropylacrylamide by controlled atom transfer radical polymerization. The phosphonate esters were removed after polymerization to afford poly(N-isopropylacrylamide) with a bis(phosphonic acid) moiety precisely placed at one terminus. The bis(phosphonic acid) endgroups were adsorbed onto magnetite nanoparticles to yield nanoscale complexes that were stable against any polymer desorption and that were colloidally-stable in physiological media. Thus, the bis(phosphonate) endgroup provides a robust anchoring moiety onto the magnetite. Hydrodynamic sizes of the complexes were predicted with a density distribution model and using the measured sizes of the magnetite cores. Good agreement between the measured and predicted hydrodynamic sizes suggested that the complexes were primarily discrete, non-agglomerated nanoparticles. The complexes exhibited thermosensitive aggregation behavior near the lower critical solution temperature of the poly(N-isopropylacrylamide) component.

The effect of applied magnetic fields on the deformation of a biocompatible hydrophobic ferrofluid drop suspended in a viscous medium is investigated numerically and compared with experimental data. A numerical formulation for the time-dependent simulation of magnetohydrodynamics of two immiscible non-conducting fluids is used with a volume-of-fluid scheme for fully deformable interfaces. Analytical formulae for ellipsoidal drops and near-spheroidal drops are reviewed and developed for code validation. At low magnetic fields, both the experimental and numerical results follow the asymptotic small deformation theory. The value of interfacial tension is deduced from an optimal fit of a numerically simulated shape with the experimentally obtained drop shape, and appears to be a constant for low applied magnetic fields. At high magnetic fields, on the other hand, experimental measurements deviate from numerical results if a constant interfacial tension is implemented. The difference can be represented as a dependence of apparent interfacial tension on the magnetic field. This idea is investigated computationally by varying the interfacial tension as a function of the applied magnetic field and by comparing the drop shapes with experimental data until a perfect match is found. This estimation method provides a consistent correlation for the variation in interfacial tension at high magnetic fields. A conclusion section provides a discussion of physical effects which may influence the microstructure and contribute to the reported observations.

Novel hydrophilic triblock copolymers which form micelles in aqueous solution were studied by static and dynamic light scattering (SLS and DLS), small angle neutron scattering (SANS) and densitometry. The polymers were symmetric A-B-A block copolymers having two poly(ethylene oxide) (PEO) tail blocks and a polyurethane (PU) center segment that contained pendant carboxylic acids. The aggregation number of the micelles decreased with increasing PEO mass content. When attempting to fit the SANS data it was found that no single model was suitable over the entire range of block lengths and PEO mass concentrations investigated here. For the polymer with the highest aggregation number, the data were fitted with a triblock model consisting of a homogeneous core with a corona of non-interacting Gaussian chains for which only two free parameters were required: the radius of the core and the radius of gyration of the corona. In this case, the core was found to be effectively dry. At lower aggregation numbers, a star polymer model generated significantly better fits, suggesting the absence of any identifiable central core structure. Good agreement was found between the sizes measured by DLS, SANS and theoretical predictions of micelle size from a density distribution theory. These results show that when significant changes in aggregation number occur, the nanostructure of the micelle can change substantially even for polymers that are remarkably similar.

Iron oxide nanoparticles (IONPs), with a diameter of 8 nm, have been coated with two different polymers, i.e. poly(oligoethylene glycol) methyl ether acrylate (P(OEG-A)) and poly(dimethylaminoethyl acrylate) (P(DMAEA)). The polymers were attached to the nanoparticle surface using two different strategies, with the aim of creating an internal layer of P(DMAEA) and an outer shell of P(OEG-A). The subsequent polymer-stabilized IONPs were characterized using ATR, XPS and TGA, proving the presence of polymers on the IONP surfaces with a grafting density ranging from 0.05 to 0.22 chain per nm2. High grafting densities were demonstrated when the two homopolymers were assembled on the surfaces of the IONPs simultaneously. The polymer composition at the surfaces of the IONPs could be controlled by manipulating the feed ratio P(OEG-A)–P(DMAEA) present in solution. These hybrid organic–inorganic particles (70–150 nm) proved to be stable in both water and 50 vol% fetal bovine serum (FBS). In addition, zeta-potential measurements confirmed that P(OEG-A) chains effectively mask the positive charge originating from P(DMAEA) thereby limiting protein adsorption on these particles. Hybrid nanoparticles were exploited for the complexation of siRNA, thereby generating IONP siRNA nano-carriers with anti-fouling P(OEG-A) shells. The transfection efficiency was measured using human neuroblastoma SHEP cells both in the presence and in the absence of a magnetic field in FBS. The transfection efficiency was determined by both fluorescence microscopy and flow cytometry. Cytotoxicity studies revealed that the IONP carriers were non-toxic to SHEP cells. In addition, studies on the proton transverse relaxation enhancement properties of these stabilized IONPs indicated high relaxivities (∼160 s−1 per mM of Fe).

This paper investigates the static and dynamic performance of current sense methods, which exploit the resistive voltage drop across the current carrying copper trace. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. A microcontroller can be used to calibrate the copper trace resistance and implement a temperature drift compensation by means of a temperature sensor. Given that today almost every electronic device has at least one microcontroller that can provide the small computation power required for this current sensing technique, the additional cost of such a technique is small.While the proposed technique appears straightforward, theoretical modeling and hardware experiments revealed two unexpected obstacles. First, the thermal resistance between the busbar and the temperature sensor notably alters correction for the temperature drift. We found that it is possible to rectify this behavior by implementing a more sophisticated temperature compensation method inside the microcontroller. Second, it is demonstrated that the self-inductance of the busbar arrangement is not important for the dynamic behavior (frequency response) of this measurement method, and the response is determined by the mutual inductance between main loop and sense loop. Based on simulation and measurements, we demonstrated that a simple RC-compensation network can significantly improve the frequency response.

The morphological evolution of SiO2/γ-Fe2O3 nanocomposites was systematically synthesized in a one-step flame spray pyrolysis. Under these conditions, a gradual transformation from discrete γ-Fe2O3 nanoparticles to thin SiO2 coatings, segregated single γ-Fe2O3 core, and multiple γ-Fe2O3 cores within a SiO2 matrix was obtained as a function of SiO2 loading. The presence of SiO2 up to 13% has a pronounced effect on the γ-Fe2O3 crystallite structure (transforming from P4132 to Fd3m space group) and its cationic vacancy ordering. Decrease in the latter was further reflected through the intrinsic magnetic properties of the γ-Fe2O3 cores (i.e., decreasing specific saturation magnetization and increasing coercivity and exchange bias). Deviation from the magnon-type thermal dependence, T3/2 Bloch law, was observed for nanocomposites with SiO2 content above 13%. The Ms vs T curves could be fitted with the sum of an exponential component and a Bloch law component, where the magnitude of the exponential component i...

The lossless inductor current sensing method is well-known and is frequently applied in the measurement of output current in DC-DC converters due to its low cost and simplicity. This technique uses a low-pass filter that is matched to the inductance (L) and winding resistance to compensate for induced voltages due to the inductor. However, the waveform fidelity above the corner frequency of the inductor is generally poor due to large production tolerances and thermal drift. In this letter, we propose the use of a coupled sense winding, which increases the corner frequency of the sensing circuit by more than two orders of magnitude. We show, as an example, that for a 3.85 muH inductor the corner frequency of the measurement circuit can be increased from 36 Hz using the conventional approach to 5.8 kHz using the coupled sense winding method. Above the new corner frequency, a low-pass filter is still required but may now be constructed using a smaller capacitor and with improved high-frequency response.

This paper provides a thorough review of state-of-the-art current sensing techniques. It catalogues the current sensors according to the underlying physical principle in order to point out their strengths and weaknesses.

Biocompatible, hydrophobic nanoparticles show great promise as biomaterials. This paper reports the synthesis, magnetic separation, and characterization of magnetite nanoparticles with polydimethylsiloxane (PDMS) adsorbed onto their surfaces. The particle size distributions were narrowed by employing a magnetic separation/fractionation technique to remove larger particles and aggregates from an original distribution. A probability averaging method that incorporates particle size distributions of the magnetite cores derived from TEM is proposed, together with implementation of a polymer brush model for calculating the thickness of the polymer surfactant, for predicting the sizes and size distributions of these complexes in suspension. The intensity, volume, and number average size distributions in solution were predicted, and the values were compared to sizes of the complexes measured by DLS. This approach provides a tool for a more precise characterization of the size distributions of polymer-nanoparticle complexes relative to previous methods that utilized only a mean (single) core particle size. The predicted sizes of the complexes in dispersion closely approximate measured values from DLS for particles with narrow size distributions. Agreement between the predicted and measured sizes improves as the particle size distribution becomes narrower.

We present ferromagnetic resonance data from a Py film using both a pulsed inductive microwave magnetometer (PIMM) and conventional FMR. An increase in the damping is seen at low field resonances in the PIMM data from what is expected using conventional FMR. This is explained by the influence of the PIMM’s spatially inhomogeneous excitation field and quantified using an intuitive argument. We demonstrate from this derivation how excitation of non-uniform wavevectors can explain the measured increase in damping at low fields observed by the PIMM. We also present results from a coupled Py and Cobalt system, demonstrating that inductive magnetometry can be a sensitive technique for measuring exchange coupling over interfaces and surfaces.

Biocompatible, hydrophobic ferrofluids comprised of magnetite nanoparticles dispersed in polydimethylsiloxane show promise as materials for the treatment of retinal detachment. This paper focuses on the motion of hydrophobic ferrofluid droplets traveling through viscous aqueous media, whereby the movement is induced by gradients in external fields generated by small permanent magnets. A numerical method was utilized to predict the force on a spherical droplet, and then the calculated force was used to estimate the time required for the droplet to reach the permanent magnet. The calculated forces and travel times were verified experimentally.

Recently, interest in magnetic particles, particularly in the nanometre-size range, has increased significantly. The main driving forces behind this interest are both the development of improved synthesis techniques and an increase in the number of potential applications for suitable magnetic nanoparticles. A critical factor of interest in both the synthesis and the development of applications is the particle-size distribution. In this paper, we investigate three common techniques for determining the particle-size distribution of magnetic nanoparticles (electron microscopy, magnetic measurements and small-angle neutron scattering). We compare the distributions determined by each technique for two standard samples and discuss their advantages, disadvantages and limitations.

The paradigm of using nanoparticle-based formulations for drug delivery relies on their enhanced passive accumulation in the tumor interstitium. Nanoparticles with active targeting capabilities attempt to further enhance specific delivery of drugs to the tumors via interaction with overexpressed cellular receptors. Consequently, it is widely accepted that drug delivery using actively targeted nanoparticles maximizes the therapeutic benefit and minimizes the off-target effects. However, the process of nanoparticle mediated active targeting initially relies on their passive accumulation in tumors. In this article, it is demonstrated that these two tumor-targeted drug delivery mechanisms are interrelated and dosage dependent. It is reported that at lower doses, actively targeted nanoparticles have distinctly higher efficacy in tumor inhibition than their passively targeted counterparts. However, the enhanced permeability and retention effect of the tumor tissue becomes the dominant factor influencing the efficacy of both passively and actively targeted nanoparticles when they are administered at higher doses. Importantly, it is demonstrated that dosage is a pivotal parameter that needs to be taken into account in the assessment of nanoparticle mediated targeted drug delivery.

Behavioural studies underpin the weight of experimental evidence for the existence of a magnetic sense in animals. In contrast, studies aimed at understanding the mechanistic basis of magnetoreception by determining the anatomical location, structure and function of sensory cells have been inconclusive. In this review, studies attempting to demonstrate the existence of a magnetoreceptor based on the principles of the magnetite hypothesis are examined. Specific attention is given to the range of techniques, and main animal model systems that have been used in the search for magnetite particulates. Anatomical location/cell rarity and composition are identified as two key obstacles that must be addressed in order to make progress in locating and characterizing a magnetite-based magnetoreceptor cell. Avenues for further study are suggested, including the need for novel experimental, correlative, multimodal and multidisciplinary approaches. The aim of this review is to inspire new efforts towards understanding the cellular basis of magnetoreception in animals, which will in turn inform a new era of behavioural research based on first principles.

Quantitative magnetic fractionation and a published mathematical model were used to characterize between-treatment differences in gametocyte density and prevalence in 70 Papua New Guinean children with uncomplicated Plasmodium falciparum and/or Plasmodium vivax malaria randomized to one of two artemisinin combination therapies (artemether-lumefantrine or artemisinin-naphthoquine) in an intervention trial. There was an initial rise in peripheral P. falciparum gametocyte density with both treatments, but it was more pronounced in the artemisinin-naphthoquine group. Model-derived estimates of the median pretreatment sequestered gametocyte population were 21/μl for artemether-lumefantrine and 61/μl for artemisinin-naphthoquine ( P < 0.001). The median time for P. falciparum gametocyte density to fall to P < 0.001). Gametocyte prevalence modeling suggested that artemisinin-naphthoquine-treated children became gametocytemic faster (median, 2.2 days) than artemether-lumefantrine-treated children (median, 5.3 days; P < 0.001) and had a longer median P. falciparum gametocyte carriage time per individual (20 versus 13 days; P < 0.001). Clearance of P. vivax gametocytes was rapid (within 3 days) in both groups; however, consistent with the reappearance of asexual forms in the main trial, nearly 40% of children in the artemether-lumefantrine group developed P. vivax gametocytemia between days 28 and 42 compared with 3% of children in the artemisinin-naphthoquine group. These data suggest that artemisinin is less active than artemether against sequestered gametocytes. Greater initial gametocyte release after artemisinin-naphthoquine increases the period of potential P. falciparum transmission by 4 days relative to artemether-lumefantrine, but the longer elimination half-life of naphthoquine than of lumefantrine suppresses P. vivax recurrence and consequent gametocytemia.

Schistosomiasis is a chronic parasitic disease of humans, with two species primarily causing the intestinal infection: Schistosoma mansoni and Schistosoma japonicum. Traditionally, diagnosis of schistosomiasis is achieved through direct visualisation of eggs in faeces using techniques that lack the sensitivity required to detect all infections, especially in areas of low endemicity. A recently developed method termed Helmintex™ is a very sensitive technique for detection of Schistosoma eggs and exhibits 100% sensitivity at 1.3 eggs per gram of faeces, enough to detect even low-level infections. The Helminthex™ method is based on the interaction of magnetic microspheres and schistosome eggs. Further understanding the underlying egg-microsphere interactions would enable a targeted optimisation of egg-particle binding and may thus enable a significant improvement of the Helmintex™ method and diagnostic sensitivity in areas with low infection rates. We investigated the magnetic properties of S. mansoni and S. japonicum eggs and their interactions with microspheres with different magnetic properties and surface functionalization. Eggs of both species exhibited higher binding affinity to the magnetic microspheres than the non-magnetic microspheres. Binding efficiency was further enhanced if the particles were coated with streptavidin. Schistosoma japonicum eggs bound more microspheres compared with S. mansoni. However, distinct differences within eggs of each species were also observed when the distribution of the number of microspheres bound per egg was modelled with double Poisson distributions. Using this approach, both S. japonicum and S. mansoni eggs fell into two groups, one having greater affinity for magnetic microspheres than the other, indicating that not all eggs of a species exhibit the same binding affinity. Our observations suggest that interaction between the microspheres and eggs is more likely to be related to surface charge-based electrostatic interactions between eggs and magnetic iron oxide rather than through a direct magnetic interaction., This work was funded by grants from the Australian Research Council (ARC) and National Health and Medical Research Council (NHMRC) of Australia, a University of Western Australia/University of Queensland (Australia) Bilateral Research Collaboration Award as well as grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS) in Brazil. Travel to Australia by RRFC was funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil. SK is funded by an NHMRC Early Career Fellowship (GNT 1052760). LG is the beneficiary of a post-doctoral grant from the AXA Research Fund (Europe).

Superparamagnetic maghemite (γ-Fe2O3) nanoparticles of tunable diameters and silica-coated maghemite (SiO2/γ-Fe2O3) nanoparticles of controllable morphology were successfully synthesized using a on...

We report issues associated with the calibration of a biased target ion beam deposition system. Variations in deposition rates and oxygen flow have been observed when depositing individual metal oxide films immediately after films deposited from different targets as compared to depositions following films from the same target.

This study investigated the thermal behaviour of the fcc ↔ hcp martensitic transformation of Co–Ni alloys. The transformation was found to be incomplete in both directions upon cooling and heating. Upon thermal cycling, the transformation, as detected by differential scanning calorimetry, diminished rapidly, indicating that the transformation was highly irreversible. Optical microscopic observation revealed that surface reliefs appeared on pre-polished surfaces upon forward transformation, but did not disappear upon the reverse transformation, implying that the transformation also exhibited mechanical irreversibility. The irreversibility is explained on the basis of multiple choice of crystalline shuffling along 1 / 6 〈 1 1 2 ¯ 〉 { 1 1 1 } fcc for the fcc ↔ hcp transformation. These observations suggest that the fcc ↔ hcp martensitic transformation system in Co–Ni is not suitable for thermomechanical shape memory effect, which requires high reversibility of the transformation both crystallographically and mechanically. It is regarded that this rule is generic and applicable to other fcc ↔ hcp transformation systems.

A rate dependence of the magnetic domain structure has been observed in a Pt/Co multilayer. The form of the domain structure as a function of the rate of change of magnetization was studied using nanosecond pulsed magnetic fields. At low fields the magnetization pattern consists of a dendritic like growth of the domains. As the magnitude of the pulse field is increased the patterns change to a more circular structure with smooth boundaries. The change in structure can be quantified and is discussed in terms of a field dependence where different behaviors can be clearly identified. The structure observed results from a narrowing of the distribution of energy barriers to reversal as the field is increased.

We report the synthesis, characterisation and evaluation of the in vitro biocompatibility of polymeric nanoparticles with both magnetic and upconverting fluorescent properties. The particles consist of superparamagnetic iron oxide nanoparticles and upconverting NaYF4:Yb,Er nanoparticles co-encapsulated within a poly(glycidyl methacrylate) sphere. Two different upconverting nanoparticles (10 nm α-NaYF4:Yb,Er and 50 nm β-NaYF4:Yb,Er) were synthesised and the optical and magnetic properties of the composite polymeric nanoparticle systems assessed by near infra-red laser spectroscopy, SQUID magnetometry and proton relaxometry. A live-dead assay was used to assess the viability of PC-12 neural cells incubated with varying concentrations of the nanoparticles. The composite nanoparticles produced no observed impact on cellular viability even at concentrations as high as 1000 μg mL(-1). Confocal microscopy revealed uptake of nanoparticles by PC-12 cells and peri-nuclear cytoplasmic localisation. Both particle systems show favourable magnetic properties. However, only the nanospheres containing 50 nm β-NaYF4:Yb,Er were suitable for optical tracking because the presence of iron oxide within the composites imparts a significant quenching of the upconversion emission. This study demonstrates the size and phase of the upconverting nanoparticles are important parameters that have to be taken into account in the design of multimodal nanoparticles using co-encapsulation strategies.

Large metal–oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate co-ligand. The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate co-ligand structure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length.

The coercivity, time dependent magnetic properties and reversible magnetization behavior for a series of neodymium enriched alloys based on Nd/sub 2/Fe/sub 14/B has been investigated. These studies were carried out in an attempt to elucidate the dramatic increase in the coercivity in these materials with increasing dilution of the magnetic phase (Nd/sub 2/Fe/sub 14/B). Good correlation between the coercivity and the relative average linear sparing between magnetic grains was found for all but the lowest Nd content. As the Nd content is increased the reversible magnetization associated with domain wall pinning decreases. At high dilutions the reversible magnetization behavior is consistent with the predictions of a Stoner-Wohlfarth model of an assembly of noninteracting single domain particles. The magnetic viscosity parameter, /spl Lambda/, does not vary consistently with dilution or coercivity.

Magnetic force microscopy occupies a special niche in the array of techniques which are currently available for imaging magnetic structures of high energy permanent magnet materials, yielding high resolution data under ambient conditions on bulk samples. The high anisotropies of permanent magnet samples mean that to a good approximation the tip stray field does not modify the magnetic state of the sample. However strong stray fields, of the order of 1 Tesla, may be experienced by a tip in close proximity to the sample. These stray fields are known to perturb the magnetic state of the tip considerably. As a result, contrast may be generated between neighboring domains, or at domain boundary walls or a combination of both, depending on the degree of perturbation of the tip. Examples demonstrating this variation with a series of batch-fabricated tips with various magnetic coatings ranging in coercivity from ∼1400 Oe to Oe are presented. The origin of the different types of observed contrast is discussed, and it is shown that very low coercivity tips coated with Fe nanoparticles embedded in a SiO 2 matrix provide the most readily understood contrast, and have an additional benefit in that they are `self-focusing'. That is, the active magnetic volume scales with the characteristic dimension of the sample domain structure. Image interpretation is also discussed in the context of specific MFM images from samples of neodymium iron boron (sintered, melt-quenched and nanocomposite) and barium ferrite.

Zero-field magnetic viscosity measurements at temperatures between 2 and 30 K were made on a sample of chemically disordered FePt nanoparticles prepared by solution phase chemical synthesis. The data have been used to calculate the apparent magnetic-moment-weighted energy barrier distribution for the FePt. This distribution is composed of a log–normal distribution plus a second distribution that is well described by an exponential decay of barrier frequency with increasing barrier height. The two distributions contribute approximately equally to the overall distribution.

The self-assembly of nanoparticles is an efficient and precise method to fabricate nanoscale devices. By manipulating iron oxide nanoparticles in suspension with an external field to form magnetically directed linear assemblies, we demonstrate the feasibility of using this structure to template the synthesis of PEDOT:PSS conducting polymer nanowires in suspension. Furthermore these conducting wires can be assembled on interdigitated electrodes to form an array of conducting nanowires.