Flame-Made Doped Iron Oxide Nanoparticles as Tracers for Magnetic Particle Imaging

Magnetic particle imaging (MPI) is an emerging imaging modality that shows potential in tumor imaging, cell tracking, and angiography. It uses the signal generated from superparamagnetic iron oxide nanoparticles (SPIONs) with zero attenuation in tissue, showing excellent sensitivity and contrast. MPI resolution and sensitivity are dependent on the nonlinear dynamic magnetization of the SPION tracer and can be improved by tuning their magnetic properties. Doping SPIONs with manganese or zinc is an effective and biocompatible route to modify the magnetic properties of SPIONs. This study developed SPIONs doped with manganese or zinc as MPI tracers using flame spray pyrolysis (FSP), a highly scalable synthesis technique. The MPI performance was evaluated with a MOMENTUM imager. Postsynthesis citrate coating and filtration significantly enhanced the MPI resolution of SPIONs. The Zn-doped SPIONs exhibited the best resolution, while Mn-doped SPIONs showed the highest sensitivity. The overall MPI performance of all tracers was closely linked to their magnetic diameter and susceptibility, but deviated noticeably from the predictions of the Langevin model. Zn-doped SPIONs were encapsulated in a water-dispersible nanocarrier using flash nanoprecipitation (FNP), circumventing the need for citrate coating while preserving MPI performance. These findings show that the hydrodynamic size, size distribution, and composition of the SPIONs are critical to MPI performance and highlight the potential of combining FSP and FNP for large-scale production of the MPI tracers.

Controlled Synthesis of Copper Sulfide Nanoparticles in Oxygen-Deficient Conditions Using Flame Spray Pyrolysis (FSP) and Its Potential Application

The objective of this study is to investigate the influence of various process parameters, such as the fuel-to-oxygen ratio, precursor flow rate, co-flow rate, and different metal-to-sulfur ratios on the properties of metal sulfide particles synthesized via flame spray pyrolysis (FSP). The particle size increases with increasing dispersion oxygen flow and copper sulfide is obtained only when the fuel-to-oxygen ratio is equal to or higher than 1.5. The temperature of the flame rises with an increasing precursor flow rate and copper sulfide is formed at a precursor flow rate of 5 mL min-1 or lower, while contamination occurs above 5 mL min-1. A Co-flow rate above 100 L min-1 is required to cool the aerosol stream before deposition on the filter. A pure copper sulfide phase is produced when sulfur is more than 5 times in molar ratio compared to Cu in the liquid solution and particle size decreases with increasing sulfur concentration. This research will contribute to a better understanding of the fundamental formation process of metal sulfides under oxygen-lean gas-phase conditions and serve as a milestone in optimizing synthesis parameters for various applications.

Large-scale production of superparamagnetic iron oxide nanoparticles by flame spray pyrolysis: In vitro biological evaluation for biomedical applications

Despite the large number of synthesis methodologies described for superparamagnetic iron oxide nanoparticles (SPIONs), the search for their large-scale production for their widespread use in biomedical applications remains a mayor challenge. Flame Spray Pyrolysis (FSP) could be the solution to solve this limitation, since it allows the fabrication of metal oxide nanoparticles with high production yield and low manufacture costs. However, to our knowledge, to date such fabrication method has not been upgraded for biomedical purposes. Herein, SPIONs have been fabricated by FSP and their surface has been treated to be subsequently coated with dimercaptosuccinic acid (DMSA) to enhance their colloidal stability in aqueous media. The final material presents high quality in terms of nanoparticle size, homogeneous size distribution, long-term colloidal stability and magnetic properties. A thorough in vitro validation has been performed with peripheral blood cells and mesenchymal stem cells (hBM-MSCs). Specifically, hemocompatibility studies show that these functionalized FSP-SPIONs-DMSA nanoparticles do not cause platelet aggregation or impair basal monocyte function. Moreover, in vitro biocompatibility assays show a dose-dependent cellular uptake while maintaining high cell viability values and cell cycle progression without causing cellular oxidative stress. Taken together, the results suggest that the FSP-SPIONs-DMSA optimized in this work could be a worthy alternative with the benefit of a large-scale production aimed at industrialization for biomedical applications.

Vapor-phase production of nanomaterials

The synthesis of nanomaterials, with characteristic dimensions of 1 to 100 nm, is a key component of nanotechnology. Vapor-phase synthesis of nanomaterials has numerous advantages such as high product purity, high-throughput continuous operation, and scalability that have made it the dominant approach for the commercial synthesis of nanomaterials. At the same time, this class of methods has great potential for expanded use in research and development. Here, we present a broad review of progress in vapor-phase nanomaterial synthesis. We describe physically-based vapor-phase synthesis methods including inert gas condensation, spark discharge generation, and pulsed laser ablation; plasma processing methods including thermal- and non-thermal plasma processing; and chemically-based vapor-phase synthesis methods including chemical vapor condensation, flame-based aerosol synthesis, spray pyrolysis, and laser pyrolysis. In addition, we summarize the nanomaterials produced by each method, along with representative applications, and describe the synthesis of the most important materials produced by each method in greater detail.

Iron Oxide Nanoparticles as T1 Contrast Agents for Magnetic Resonance Imaging: Fundamentals, Challenges, Applications, and Prospectives

Gadolinium-based chelates are a mainstay of contrast agents for magnetic resonance imaging (MRI) in the clinic. However, their toxicity elicits severe side effects and the Food and Drug Administration has issued many warnings about their potential retention in patients' bodies, which causes safety concerns. Iron oxide nanoparticles (IONPs) are a potentially attractive alternative, because of their nontoxic and biodegradable nature. Studies in developing IONPs as T1 contrast agents have generated promising results, but the complex, interrelated parameters influencing contrast enhancement make the development difficult, and IONPs suitable for T1 contrast enhancement have yet to make their way to clinical use. Here, the fundamental principles of MRI contrast agents are discussed, and the current status of MRI contrast agents is reviewed with a focus on the advantages and limitations of current T1 contrast agents and the potential of IONPs to serve as safe and improved alternative to gadolinium-based chelates. The past advances and current challenges in developing IONPs as a T1 contrast agent from a materials science perspective are presented, and how each of the key material properties and environment variables affects the performance of IONPs is assessed. Finally, some potential approaches to develop high-performance and clinically relevant T1 contrast agents are discussed.

Mechanism of magnetization reduction in iron oxide nanoparticles

Iron oxide nanoparticles are presently considered as main work horses for various applications including targeted drug delivery and magnetic hyperthermia. Several questions remain unsolved regarding the effect of size onto their overall magnetic behavior. One aspect is the reduction of magnetization compared to bulk samples. A detailed understanding of the underlying mechanisms of this reduction could improve the particle performance in applications. Here we use a number of complementary experimental techniques including neutron scattering and synchrotron X-ray diffraction to arrive at a consistent conclusion. We confirm the observation from previous studies of a reduced saturation magnetization and argue that this reduction is mainly associated with the presence of antiphase boundaries, which are observed directly using high-resolution transmission electron microscopy and indirectly via an anisotropic peak broadening in X-ray diffraction patterns. Additionally small-angle neutron scattering with polarized neutrons revealed a small non-magnetic surface layer, that is, however, not sufficient to explain the observed loss in magnetization alone.

Single-Step Fabrication of Polymer Nanocomposite Films

Polymer nanocomposites are employed in (micro)electronic, biomedical, structural and optical applications. Their fabrication is challenging due to nanoparticle (filler) agglomeration and settling, increased viscosity of blended solutions and multiple tedious processing steps, just to name a few. Often this leads to an upper limit for filler content, requirements for filler⁻polymer interfacial chemistry and expensive manufacturing. As a result, novel but simple processes for nanocomposite manufacture that overcome such hurdles are needed. Here, a truly single-step procedure for synthesis of polymer nanocomposite films, structures and patterns at high loadings of nanoparticles (for example, >24 vol %) for a variety of compositions is presented. It is highly versatile with respect to rapid preparation of films possessing multiple layers and filler content gradients even on untreated challenging substrates (paper, glass, polymers). Such composites containing homogeneously dispersed nanoparticles even at high loadings can improve the mechanical strength of hydrogels, load-bearing ability of fragile microstructures, gas permeability in thin barriers, performance of dielectrics and device integration in stretchable electronics.

Characterization of typical metal particles during haze episodes in Shanghai, China

Aerosol particles were collected during three heavy haze episodes at Shanghai in the winter of 2013. Transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy was used to study the morphology and speciation of typical metal particles at a single-particle level. In addition, time-of-flight aerosol mass spectrometry (ATOFMS) was applied to identify the speciation of the Fe-containing particles. TEM analysis indicated that various metal-containing particles were hosted by sulfates, nitrates, and oxides. Fe-bearing particles mainly originated from vehicle emissions and/or steel production. Pb-, Zn-, and Sb-bearing particles were mainly contributed by anthropogenic sources. Fe-bearing particles were clustered into six groups by ATOFMS: Fe-Carbon, Fe-Inorganic, Fe-Trace metal, Fe-CN, Fe-PO_3, and Fe-NO₃. ATOFMS data suggested that Fe-containing particles corresponded to different origins, including industrial activities, resuspension of dusts, and vehicle emissions. Fe-Carbon and Fe-CN particles displayed significant diurnal variation, and high levels were observed during the morning rush hours. Fe-Inorganic and Fe-Trace metal particle levels peaked at night. Furthermore, Fe-Carbon and Fe-PO₃ were mainly concentrated in the fine particles. Fe-CN, Fe-Inorganic, and Fe-Trace metal exhibited bimodal distribution. The mixing state of the particles revealed that all Fe-bearing particles tended to be mixed with sulfate and nitrate. The data presented herein is essential for elucidating the origin, evolution processes, and health effects of metal-bearing particles.

Functional magnetic porous silica for T 1-T 2 dual-modal magnetic resonance imaging and pH-responsive drug delivery of basic drugs

A smart magnetic-targeting drug carrier γ-Fe₂O₃@p-silica comprising a γ-Fe₂O₃ core and porous shell has been prepared and characterized. The particles have a uniform size of about 60 nm, and a porous shell of thickness 3 nm. Abundant hydroxyl groups and a large surface area enabled the γ-Fe₂O₃@p-silica to be readily loaded with a large payload of the basic model drug rhodamine B (RB) (up to 73 mg g^-1). Cytotoxicity assays of the γ-Fe₂O₃@p-silica particles indicated that the particles were biocompatible and suitable for carrying drugs. It was found that the RB was released rapidly at pH 5.5 but at pH 7.4 the rate and extent of release was greatly attenuated. The particles therefore demonstrate an excellent pH-triggered drug release. In addition, the γ-Fe₂O₃@p-silica particles could be tracked by magnetic resonance imaging (MRI). A clear dose-dependent contrast enhancement in both T ₁-weighted and T ₂-weighted MR images indicated the potential of the γ-Fe₂O₃@p-silica particles to act as dual-mode T ₁ and T ₂ MRI contrast agents.

Lead (Pb2+) and copper (Cu2+) remediation from water using superparamagnetic maghemite (γ-Fe2O3) nanoparticles synthesized by Flame Spray Pyrolysis (FSP)

Superparamagnetic maghemite (γ-Fe₂O₃) nanoparticles of controllable morphology were successfully synthesized using a flame spray pyrolysis (FSP) technique. Their physico-chemical properties, size, morphology, and surface chemistries were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), selected area electron diffraction patterns (SAED), SEM-EDX, scanning electron microscopy (SEM), and pH_ZPC(6.3). Elemental contents before and after adsorption were identified using energy dispersive X-ray fluorescence (ED-XRF), energy dispersive X-ray analysis (EDX) and elemental mapping. Surface area (S_BET 79.35m²/g) and size distribution analyses were conducted using a surface area analyzer and dynamic light scattering (DLS), respectively. The magnetic moment (44.5 at 300K and 50.16 at 2K) was determined using a physical properties measurement system (PPMS). The first adsorption study using γ-Fe₂O₃ nanoparticles synthesized by FSP to successfully remediate Pb²⁺ and Cu²⁺ from water is reported. Batch adsorption studies were carried out. An optimum pH of 5.0 was studied for Pb²⁺ and Cu²⁺ removal. Pb²⁺ and Cu²⁺ removal mechanisms by these maghemite nanoparticles were presented. The adsorption of Pb²⁺ and Cu²⁺ was highly pH-dependent. The metal ion uptake was mainly governed by electrostatic attractions. Sorption kinetic data followed the pseudo-second-order model. The Freundlich, Langmuir, Redlich-Peterson, Radke and Sips adsorption isotherm models were applied to interpret equilibrium data. The Freundlich and Langmuir isotherm equations best fit the respective equilibrium data for Pb²⁺ and Cu²⁺. The maximum Langmuir adsorption capacities of these maghemite nanoparticles were 68.9mg/g at 45°C for Pb²⁺ and 34.0mg/g at 25 °C for Cu²⁺. Thus, these maghemite nanoparticles made by FSP were readily prepared, characterized and showed promise for remediating heavy metal ions from aqueous solutions.

Disposable micro stir bars by photodegradable organic encapsulation of hematite–magnetite nanoparticles

We present a novel method to synthesize microscale stirring bars by the anisotropic assembly of magnetite nanoparticles to overcome diffusion-limited mixing in micro-vessels.

Citrate precursor synthesis and multifunctional properties of YCrO3 nanoparticles

Monophasic and multifunctional YCrO₃ nanoparticles (22 nm) with a high surface area of 344 m² g⁻¹ exhibit well-defined multiferroic characteristics.

Structure evolution of nanoparticulate Fe2O3

The atomic structure and properties of nanoparticulate Fe2O3 are characterized starting from its smallest Fe2O3 building unit through (Fe2O3)n clusters to nanometer-sized Fe2O3 particles. This is achieved by combining global structure optimizations at the density functional theory level, molecular dynamics simulations by employing tailored, ab initio parameterized interatomic potential functions and experiments. With the exception of nearly tetrahedral, adamantane-like (Fe2O3)2 small (Fe2O3)n clusters assume compact, virtually amorphous structures with little or no symmetry. For n = 2-5 (Fe2O3)n clusters consist mainly of two- and three-membered Fe-O rings. Starting from n = 5 they increasingly assume tetrahedral shape with the adamantane-like (Fe2O3)2 unit as the main building block. However, the small energy differences between different isomers of the same cluster-size make precise structural assignment for larger (Fe2O3)n clusters difficult. The tetrahedral morphology persists for Fe2O3 nanoparticles with up to 3 nm in diameter. Simulated crystallization of larger nanoparticles with diameters of about 5 nm demonstrates pronounced melting point depression and leads to formation of ε-Fe2O3 single crystals with hexagonal morphology. This finding is in excellent agreement with the results obtained for Fe2O3 nanopowders generated by laser vaporization and provides the first direct indication that ε-Fe2O3 may be thermodynamically the most stable phase in this size regime.

Real-Time Nanoparticle-Cell Interactions in Physiological Media by Atomic Force Microscopy

Particle-cell interactions in physiological media are important in determining the fate and transport of nanoparticles and biological responses to them. In this work, these interactions are assessed in real time using a novel atomic force microscopy (AFM) based platform. Industry-relevant CeO2 and Fe2O3 engineered nanoparticles (ENPs) of two primary particle sizes were synthesized by the flame spray pyrolysis (FSP) based Harvard Versatile Engineering Nanomaterials Generation System (Harvard VENGES) and used in this study. The ENPs were attached on AFM tips, and the atomic force between the tip and lung epithelia cells (A549), adhered on a substrate, was measured in biological media, with and without the presence of serum proteins. Two metrics were used to assess the nanoparticle cell: the detachment force required to separate the ENP from the cell and the number of bonds formed between the cell and the ENPs. The results indicate that these atomic level ENP-cell interaction forces strongly depend on the physiological media. The presence of serum proteins reduced both the detachment force and the number of bonds by approximately 50% indicating the important role of the protein corona on the particle cell interactions. Additionally, it was shown that particle to cell interactions were size and material dependent.

Structure and magnetic properties of (Fe2O3)n clusters (n = 1–5)

Global minimum structures of (Fe₂O₃)_n clusters (n = 1–5) determined for the first time in this size range show weak dependence of the structure and relative stabilities of different isomers on their magnetic states.

Nanoparticle-nanoparticle interactions in biological media by atomic force microscopy

Particle-particle interactions in physiological media are important determinants for nanoparticle fate and transport. Herein, such interactions are assessed by a novel atomic force microscopy (AFM)-based platform. Industry-relevant CeO2, Fe2O3, and SiO2 nanoparticles of various diameters were made by the flame spray pyrolysis (FSP)-based Harvard Versatile Engineering Nanomaterials Generation System (Harvard VENGES). The nanoparticles were fully characterized structurally and morphologically, and their properties in water and biological media were also assessed. The nanoparticles were attached on AFM tips and deposited on Si substrates to measure particle-particle interactions. The corresponding force was measured in air, water, and biological media that are widely used in toxicological studies. The presented AFM-based approach can be used to assess the agglomeration potential of nanoparticles in physiological fluids. The agglomeration potential of CeO2 nanoparticles in water and RPMI 1640 (Roswell Park Memorial Institute formulation 1640) was inversely proportional to their primary particle (PP) diameter, but for Fe2O3 nanoparticles, that potential is independent of PP diameter in these media. Moreover, in RPMI+10% Fetal Bovine Serum (FBS), the corona thickness and dispersibility of the CeO2 are independent of PP diameter, while for Fe2O3, the corona thickness and dispersibility were inversely proportional to PP diameter. The present method can be combined with dynamic light scattering (DLS), proteomics, and computer simulations to understand the nanobio interactions, with emphasis on the agglomeration potential of nanoparticles and their transport in physiological media.

A Perspective on the Flame Spray Synthesis of Photocatalyst Nanoparticles

The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active catalysts, that is, high surface area and surface energetics. For these reasons, FSP finds applications in various thermally inducible catalytic reactions. However, the design and synthesis of photocatalysts by FSP requires a knowledge set which is different from that established for thermal catalysts. Unknown to many, this has resulted in frustrations to those entering the field unprepared, especially since FSP appears to be an elegant tool in synthesising oxide nanoparticles of any elemental construct. From simple oxide to doped-oxide, and mixed metal oxide to the in situ deposition of noble metals, this Perspective gives an overview on the development of photocatalysts made by FSP in the last decade that led to a better understanding of the design criteria. Various challenges and opportunities are also highlighted, especially those beyond simple metal oxides, which perhaps contain the greatest potential for the exploitation of photocatalysts design by FSP.

Double-faced γ-Fe2O3||SiO2 nanohybrids: flame synthesis, in situ selective modification and highly interfacial activity

Double-faced γ-Fe2O3||SiO2 nanohybrids (NHs) and their in situ selective modification on silica faces with the 3-methacryloxypropyltrimethoxysilane molecules have been successfully prepared by a simple, rapid and scalable flame aerosol route. The double-faced NHs perfectly integrate magnetic hematite hemispheres and non-magnetic silica parts into an almost intact nanoparticle as a result of phase segregation during the preparation process. The unique feature allows us to easily manipulate these particles into one-dimensional chain-like nanostructures. On the other hand, in situ selectively modified double-faced γ-Fe2O3||SiO2 NHs possess excellent interfacial activities, which can assemble into many interesting architectures, such as interfacial film, magnetic responsive capsules, novel magnetic liquid marbles and so forth. The modified NHs prefer to assemble at the interface of water-oil or oil-water systems. It is believed that the highly interfacial active NHs are not only beneficial for the development of interface reaction in a miniature reactor, but also very promising functional materials for other smart applications.

The effect of polymer coatings on proton transverse relaxivities of aqueous suspensions of magnetic nanoparticles

Iron oxide magnetic nanoparticles are good candidates for magnetic resonance imaging (MRI) contrast agents due to their high magnetic susceptibilities. Here we investigate 19 polyether-coated magnetite nanoparticle systems comprising three series. All systems were synthesized from the same batch of magnetite nanoparticles. A different polyether was used for each series. Each series comprised systems with systematically varied polyether loadings per particle. A highly significant (p < 0.0001) linear correlation (r = 0.956) was found between the proton relaxivity and the intensity-weighted average diameter measured by dynamic light scattering in the 19 particle systems studied. The intensity-weighted average diameter measured by dynamic light scattering is sensitive to small number fractions of larger particles/aggregates. We conclude that the primary effect leading to differences in proton relaxivity between systems arises from the small degree of aggregation within the samples, which appears to be determined by the nature of the polymer and, for one system, the degree of polymer loading of the particles. For the polyether coatings used in this study, any changes in relaxivity from differences in water exclusion or diffusion rates caused by the polymer are minor in comparison with the changes in relaxivity resulting from variations in the degree of aggregation.

Exchange bias effect in alloys and compounds

The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

Flame spray pyrolysis: An enabling technology for nanoparticles design and fabrication

Combustion of appropriate precursor sprays in a flame spray pyrolysis (FSP) process is a highly promising and versatile technique for the rapid and scalable synthesis of nanostuctural materials with engineered functionalities. The technique was initially derived from the fundamentals of the well-established vapour-fed flame aerosols reactors that was widely practised for the manufacturing of simple commodity powders such as pigmentary titania, fumed silica, alumina, and even optical fibers. In the last 10 years however, FSP knowledge and technology was developed substantially and a wide range of new and complex products have been synthesised, attracting major industries in a diverse field of applications. Key innovations in FSP reactor engineering and precursor chemistry have enabled flexible designs of nanostructured loosely-agglomerated powders and particulate films of pure or mixed oxides and even pure metals and alloys. Unique material morphologies such as core-shell structures and nanorods are possible using this essentially one step and continuous FSP process. Finally, research challenges are discussed and an outlook on the next generation of engineered combustion-made materials is given.

Assembly of polyethylenimine-based magnetic iron oxide vectors: insights into gene delivery

The use of a nonviral magnetic vector, comprised of magnetic iron oxide nanoparticles (MNP), polyethylenimine (PEI), and plasmid DNA, for transfection of BHK21 cells under a magnetic field is presented. Four different vector configurations were studied by systematically varying the mixing order of MNP, PEI, and DNA. The assembly of the vector has significant effects on its vector size, surface charge, cellular uptake, and level of gene expression. Mixing MNP with PEI first improved MNP stability, giving a narrow aggregate size distribution and positive surface charge at physiological pH, which in turn facilitated DNA binding onto MNP. The presence of serum in culture media improves vector dispersion and alters the surface charge of all vectors to negative charge, indicating serum protein adsorption. Cellular uptake was greater for larger vectors than the smaller vectors due to enhanced gravitational and magnetic aided sedimentation onto the cells. High MNP uptake by the cells, however, does not inevitably lead to increase gene expression efficiency. It can be shown that besides vector uptake, gene expression is affected by extracellular factors such as premature DNA release from MNP and DNA degradation by serum as well as intracellular factors such as vector lysosomal degradation, inability of DNA to detach from MNP, and cytotoxic effects of MNP at high uptake. Some of these extra- and intracellular properties are shown to be mediated by the presence of PEI.

GAS-PHASE FLAME SYNTHESIS AND PROPERTIES OF MAGNETIC IRON OXIDE NANOPARTICLES WITH REDUCED OXIDATION STATE

Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane.

Experimental validation of proton transverse relaxivity models for superparamagnetic nanoparticle MRI contrast agents

Analytical models of proton transverse relaxation rate enhancement by magnetic nanoparticles were tested by making measurements on model experimental systems in a field of 1.4 T. Proton relaxivities were measured for five aqueous suspensions of iron oxide (maghemite) nanoparticles with nominal mean particle sizes of 6, 8, 10, 11, and 13 nm. Proton relaxivity increased with mean particle size ranging from 13 s(-1) mM Fe(-1) for the 6 nm sample, up to 254 s(-1) mM Fe(-1) for the 13 nm sample. A strong correlation between the measured and predicted values of the relaxivity was observed, with the predicted values being consistently higher than the measured values. The results indicate that the models give a reasonable agreement with experimental results and hence can be used as the basis for the design of new magnetic resonance imaging contrast and labelling agents.

Development and optimization of iron- and zinc-containing nanostructured powders for nutritional applications

Reducing the size of low-solubility iron (Fe)-containing compounds to nanoscale has the potential to improve their bioavailability. Because Fe and zinc (Zn) deficiencies often coexist in populations, combined Fe/Zn-containing nanostructured compounds may be useful for nutritional applications. Such compounds are developed here and their solubility in dilute acid, a reliable indicator of iron bioavailability in humans, and sensory qualities in sensitive food matrices are investigated. Phosphates and oxides of Fe and atomically mixed Fe/Zn-containing (primarily ZnFe2O4) nanostructured powders were produced by flame spray pyrolysis (FSP). Chemical composition and surface area were systematically controlled by varying precursor concentration and feed rate during powder synthesis to increase solubility to the level of ferrous sulfate at maximum Fe and Zn content. Solubility of the nanostructured compounds was dependent on their particle size and crystallinity. The new nanostructured powders produced minimal color changes when added to dairy products containing chocolate or fruit compared to the changes produced when ferrous sulfate or ferrous fumarate were added to these foods. Flame-made Fe- and Fe/Zn-containing nanostructured powders have solubilities comparable to ferrous and Zn sulfate but may produce fewer color changes when added to difficult-to-fortify foods. Thus, these powders are promising for food fortification and other nutritional applications.