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Magnetic nanomaterials (MNMs) have attracted significant interest in the past few decades because of their unique properties such as superparamagnetism, which results from the influence of thermal energy on a ferromagnetic nanoparticle. In the superparamagnetic size regime, the moments of nanoparticles fluctuate as a result of thermal energy. To understand the fundamental behavior of superparamagnetism and develop relevant potential applications, various preparation routes have been explored to produce MNMs with desired properties and structures. However, some challenges remain for the preparation of well-defined magnetic nanostructures, including exchange-coupled nanomagnets, which are considered as the next generation of advanced magnets. In such a case, effective synthetic methods are required to achieve control over the chemical composition, size, and structure of MNMs. For instance, liquid-phase chemical syntheses, a set of emerging approaches to prepare various magnetic nanostructures, facilitate precise control over the nucleation and specific growth processes of nanomaterials with diverse structures. Among them, the high-temperature organic-phase method is an indispensable one in which the microstructures and physical/chemical properties of MNMs can be tuned by controlling the reaction conditions such as precursor, surfactant, or solvent amounts, reaction temperature or time, reaction atmosphere, etc. In this Account, we present an overview of our progress on the chemical synthesis of various MNMs, including monocomponent nanostructures (e.g., metals, metal alloys, metal oxides/carbides) and multicomponent nanostructures (heterostructures and exchange-coupled nanomagnets). We emphasize the high-temperature organic-phase synthetic method, on which we have been focused over the past decade. Notably, multicomponent nanostructures, obtained by growing or incorporating different functional components together, not only retain the functionalities of each single component but also possess synergic properties that emerge from interfacial coupling, with improved magnetic, optical, or catalytic features. Herein, potential applications of MNMs are covered in three representative areas: biomedicine, catalysis, and environmental purification. Regarding biomedicine, MNMs can detect or target biological entities after being modified with specific biomolecules, and they can be applied to magnetic resonance imaging, imaging-guided drug delivery, and photothermal therapy. Apart from their magnetic features, the catalytic performance of some MNMs resulting from their highly specific chemical components and surface structure will be briefly introduced, highlighting its impact in the methanol oxidation reaction, the oxygen reduction reaction, the oxygen and hydrogen evolution reactions, and the Fischer-Tropsch synthesis. Finally, environmental purification, primarily for water remediation, will be highlighted with two main aspects: the effective capture of bacteria and the removal of adverse ions in wastewater. We hope that this Account will clarify the progress on the controllable preparation of MNMs with specific compositions, sizes, and structures and generate broad interest in the realms of biomedicine and catalysis as well as in environmental issues and other potential applications. [ABSTRACT FROM AUTHOR]

Hybridnanoarchitectures are among the most promising nanotechnology-enabledmaterials for biomedical applications. Interfacing of nanoparticleswith active materials gives rise to the structures with unique multiplefunctionality. Superparamagnetic iron oxide nanoparticles particlesSPION are widely employed in the biology and in developing of advancedmedical technologies. Polymeric micelles offer the advantage of multifunctionalcarriers which can serve as delivery vehicles carrying nanoparticles,hydrophobic chemotherapeutics and other functional materials and molecules.Stimuli-responsive polymers are especially attractive since theirproperties can be modulated in a controlled manner. Here we reporton multifunctional thermo-responsive poly(N-isopropylacrylamide-co-acrylamide)-block-poly(ε-caprolactone)random block copolymer micelles as magnetic hyperthermia-mediatedpayload release and imaging agents. The combination of copolymers,nanoparticles and doxorubicin drug was tailored the way that the loadedmicelles were cable to respond to magnetic heating at physiologically-relevanttemperatures. A surface functionalization of the micelles with theintegrin β4 antibody and consequent interfacing of the resultingnanobio hybrid with squamous head and neck carcinoma cells which isknown to specifically over-express the A9 antigen resulted in concentrationof the micelles on the surface of cells. No inherent cytotoxicitywas detected for the magnetic micelles without external stimuli application.Furthermore, SPION-loaded micelles demonstrate significant MRI contrastenhancement abilities. [ABSTRACT FROM AUTHOR]

We report the synthesis of Fe3O4/silica core/shellnanoparticles and their functionalization with S-nitrosothiols.These nanoparticles are of immense interest because of their nitricoxide (NO) release capabilities in human alveolar epithelial cells.Moreover, they act as large storage reservoirs of NO that can be targetedmagnetically to the specific site with a sustainable release of NOfor up to 50 h. Such nanoparticles provide an enhancement of the biocompatibilitywith released NO while allowing intracellular accumulation ascribedto their small size. [ABSTRACT FROM AUTHOR]

We describe a simple method for synthesizing superparamagneticnanoparticles (SPIONs) as small, stable contrast agents for magneticresonance imaging (MRI) based on sulfobetaine zwitterionic ligands.SPIONs synthesized by thermal decomposition were coated with zwitterionsto impart water dispersibility and high in vivo stability throughthe nanoemulsion method. Zwitterion surfactant coating layers areformed easily on oleic acid-stabilized SPIONs via hydrophobic andvan der Waals interactions. Our zwitterion-coated SPIONs (ZSPIONs)had ultrathin (∼5 nm) coating layers with mean sizes of 12.0± 2.5 nm, as measured by dynamic light scattering (DLS). Uponincubation in 1 M NaCl and 10% FBS, the ZSPIONs showed high colloidalstabilities without precipitating, as monitored by DLS. The T2 relaxivitycoefficient of the ZSPIONs, obtained by measuring the relaxation rateon the basis of the iron concentration, was 261 mM–1 s–1. This value was much higher than that of thecommercial T2 contrast agent because of the ultrathin coating layer.Furthermore, we confirmed that ZSPIONs can be used as MR contrastagents for in vivo applications such as tumor imaging and lymph nodemapping. [ABSTRACT FROM AUTHOR]

Polycationic superparamagnetic nanoparticles (∼150–250nm) were evaluated as virucidal agents. The particles possess a core–shellstructure, with cores consisting of magnetite clusters and shellsof functional silica covalently bound to poly(hexamethylene biguanide)(PHMBG), polyethyleneimine (PEI), or PEI terminated with aziridinemoieties. Aziridine was conjugated to the PEI shell through cationicring-opening polymerization. The nanometric core–shell particlesfunctionalized with biguanide or aziridine moieties are able to bindand inactivate bacteriophage MS2, herpes simplex virus HSV-1, nonenvelopedinfectious pancreatic necrosis virus (IPNV), and enveloped viral hemorrhagicsepticaemia virus (VHSV). The virus–particle complexes canbe efficiently removed from the aqueous milieu by simple magnetocollection. [ABSTRACT FROM AUTHOR]

This Communication describes the synthesis of highly monodispersed 12 nm nickel nanocubes. The cubic shape was achieved by using trioctylphosphine and hexadecylamine surfactants under a reducing hydrogen atmosphere to favor thermodynamic growth and the stabilization of {100} facets. Varying the metal precursor to trioctylphosphine ratio was found to alter the nanoparticle size and shape from 5 nm spherical nanoparticles to 12 nm nanocubes. High-resolution transmission electron microscopy showed that the nanocubes are protected from further oxidation by a 1 nm NiO shell. Synchrotron-based X-ray diffraction techniques showed the nickel nanocubes order into [100] aligned arrays. Magnetic studies showed the nickel nanocubes have over 4 times enhancement in magnetic saturation compared to spherical superparamagnetic nickel nanoparticles. [ABSTRACT FROM AUTHOR]

The potential of superparamagnetic iron oxide nanoparticles(SPIONs)in various biomedical applications, including magnetic resonance imaging(MRI), sensing, and drug delivery, requires that their surface bederivatized to be hydrophilic and biocompatible. We report here thedesign and synthesis of a compact and water-soluble zwitterionic dopaminesulfonate (ZDS) ligand with strong binding affinity to SPIONs. Afterligand exchange, the ZDS-coated SPIONs exhibit small hydrodynamicdiameters, and stability with respect to time, pH, and salinity. Furthermore,small ZDS coated SPIONs were found to have a reduced nonspecific affinity(compared to negatively charged SPIONs) toward serum proteins; streptavidin/dyefunctionalized SPIONs were bioactive and thus specifically targetedbiotin receptors. [ABSTRACT FROM AUTHOR]

Important issues in the design of superparamagnetic iron oxide nanoparticles (SPIONs) for cancer diagnosis include stability under physiological conditions and specificity in targeting the cancer cells. In the present study, atom transfer radical polymerization (ATRP) was used to graft SPIONs with poly(glycidyl methacrylate-co-poly(ethylene glycol) methyl ether methacrylate) (SPIONs-P(GMA-co-PEGMA)). The PEGMA in the copolymer chain confers high stability to the nanoparticles in aqueous medium, and prevents recognition by macrophages with the aim of prolonging their in vivocirculation time. The GMA groups were used for conjugating the cancer targeting ligand, folic acid (FA), via‘click’ chemistry. Using this method, the amount of FA conjugated to the nanoparticles (SPIONs-P(GMA-co-PEGMA)-FA) can be readily controlled. The specificity of cellular uptake of the nanoparticles by three different cell lines was investigated. The cellular iron uptake by KB cells (human epidermoid carcinoma) after 24 h of incubation is about thirteen and five times higher than those by 3T3 fibroblasts and macrophages, respectively. No significant cytotoxicity was observed with these three types of cells. The high targeting efficiency and biocompatibility of these nanoparticles are promising features for in vivospecific targeting and detection of tumor cells which overexpress the folate receptor. [ABSTRACT FROM AUTHOR]

Highly ordered mineralized structures created by livingorganismsare often hierarchical in structure with fundamental structural elementsat nanometer scales. Proteins have been found responsible for formingmany of these structures, but the mechanisms by which these biomineralizationproteins function are generally poorly understood. To better understandits role in biomineralization, the magnetotactic bacterial protein,Mms6, which promotes the formation in vitro of superparamagnetic magnetitenanoparticles of uniform size and shape, was studied for its structureand function. Mms6 is shown to have two phases of iron binding: onehigh affinity and stoichiometric and the other low affinity, highcapacity, and cooperative with respect to iron. The protein is amphipathicwith a hydrophobic N-terminal domain and hydrophilic C-terminal domain.It self-assembles to form a micelle, with most particles consistingof 20–40 monomers, with the hydrophilic C-termini exposed onthe outside. Studies of proteins with mutated C-terminal domains showthat the C-terminal domain contributes to the stability of this multisubunitparticle and binds iron by a mechanism that is sensitive to the arrangementof carboxyl/hydroxyl groups in this domain. [ABSTRACT FROM AUTHOR]

Quantifying nanoparticle (NP) transport inside saturated porous geological media is imperative for understanding their fate in a range of natural and engineered water systems. While most studies focus upon finer grained systems representative of soils and aquifers, very few examine coarse-grained systems representative of riverbeds and gravel based sustainable urban drainage systems. In this study, we investigated the potential of magnetic resonance imaging (MRI) to image transport behaviors of nanoparticles (NPs) through a saturated coarse-grained system. MRI successfully imaged the transport of superparamagnetic NPs, inside a porous column composed of quartz gravel using T2-weighted images. A calibration protocol was then used to convert T2-weighted images into spatially resolved quantitative concentration maps of NPs at different time intervals. Averaged concentration profiles of NPs clearly illustrates that transport of a positively charged amine-functionalized NP within the column was slower compared to that of a negatively charged carboxyl-functionalized NP, due to electrostatic attraction between positively charged NP and negatively charged quartz grains. Concentration profiles of NPs were then compared with those of a convection-dispersion model to estimate coefficients of dispersivity and retardation. For the amine functionalized NPs (which exhibited inhibited transport), a better model fit was obtained when permanent attachment (deposition) was incorporated into the model as opposed to nonpermanent attachment (retardation). This technology can be used to further explore transport processes of NPs inside coarse-grained porous media, either by using the wide range of commercially available (super)paramagnetically tagged NPs or by using custom-made tagged NPs. [ABSTRACT FROM AUTHOR]

Nanotechnology provides a flexible platform for the development of effective therapeutic nanomaterials that can interact specifically with a target in a biological system and provoke a desired response. Of the nanomaterials studied, iron oxide nanoparticles have emerged as one of top candidates for cancer therapy. Their intrinsic superparamagnetism enables noninvasive magnetic resonance imaging (MRI), and their biodegradability is advantageous for in vivoapplications. A therapeutic superparamagnetic iron oxide nanoparticle (SPION) typically consists of three primary components: an iron oxide nanoparticle core that serves as both a carrier for therapeutics and contrast agent for MRI, a coating on the iron oxide nanoparticle that promotes favorable interactions between the SPION and the biological system, and a therapeutic payload that performs the designated function in vivo. Often, the design may include a targeting ligand that recognizes the receptors over-expressed on the exterior surface of cancer cells. [ABSTRACT FROM AUTHOR]

The assembly and complexation of oppositely charged colloids are important phenomena in many natural and synthetic processes. Liposome-nanoparticle assemblies (LNAs) represent an interesting hybrid system that combines “soft” and “hard” colloidal materials. This work describes the formation and characterization of gel-phase LNAs formed by the binding of anionic superparamagnetic iron oxide (SPIO) nanoparticles to cationic dipalmitoylphosphatidylcholine (DPPC)/dipalmitoyltrimethylammonium propane (DPTAP) liposomes. Particles were examined with hydrodynamic diameters below (16 nm) and above (30 nm) the cutoff reported for supported lipid bilayer formation. LNA formation with 16 nm particles was entropically driven and particles bound individually to yield “decorated” structures. In this case, increasing nanoparticle concentration yielded colloidal LNA aggregates and eventual charge inversion. In contrast, LNA formation with 30 nm particles was enthalpically driven, and the nanoparticles aggregated at the bilayer interface. These aggregates led to significant LNA aggregation and large bilayer sheets due to liposome rupture despite minimal charge screening of the liposome surface. In this case SLBs were present, but these structures were not dominant. Differences in LNA structure were also revealed through the lipid phase transition behavior. This work infers size-dependent nanoparticle binding and LNA formation mechanisms that can be used to tailor colloidal and bilayer properties. Analogies are made to polyelectrolyte patch charge heterogeneities and DNA complexation with cationic liposomes. [ABSTRACT FROM AUTHOR]

Water-dispersible superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized by thermal decomposition of iron(III) acetylacetonate in the presence of triethylene glycol (TREG). The resulting TREG-coated SPIONs were not stable, undergoing agglomeration and loss of the TREG coating under prolonged storage at 37 °C or in the presence of increased saline concentrations. To avoid these problems, stable colloidal TREG-coated SPIONs were obtained by two different procedures: (i) dimercaptosuccinic acid (DMSA) ligand-exchange reactions to obtain DMSA-coated SPIONs and (ii) chemical modification of the TREG coating. Both procedures, but especially the DMSA exchange, increased the stability of the SPION suspension. Finally, the functionality of both types of particles for biological applications was demonstrated by conjugating a model antibody to the end carboxyl groups of the SPIONs and testing the immunoreactivity of the final antibody–particle conjugates by an enzyme-linked immunosorbent assay (ELISA). [ABSTRACT FROM AUTHOR]

A one-pot colloidal reaction strategy was developed to synthesize asymmetric magnetic composite particles (AMCPs) with high anisotropy and magnetic content. The asymmetricity was established by having two portions of the particle composed of both polystyrene and silica, among which the latter was conjugated with magnetite nanoparticles. Phase separation was found to be critical in developing the asymmetric structure between the inorganic and polymer components during miniemulsion polymerization and the sol–gel reaction. Morphological control of the magnetic composite particles was achieved in a straightforward fashion by adjusting the processing parameters. These asymmetric nanomaterials with superparamagnetic and amphiphilic properties will have significant potential in biomedical applications. [ABSTRACT FROM AUTHOR]

We present a new method for three-dimensional (3D) magnetic focusing of magnetic micropartides in a microfluidic system. On-chip magnetic particle manipulation in the microchannel is achieved bya high-gradient magnetic field generated by means of a micromachined field concentrator. The system allows retention of functionalized beads in a dense plug while flowing through buffer or analyte. Slowly reducing the magnetic retention force in the presence of a flow results in controlled release of the partides into a fine streamline with regular longitudinal interpartide spacing. Alignment at haliheight of the channel is readily obtained through the symmetry of the magnetic field. A single lateral sheath flow is required to provide full 3D focusing of the micropartides in the middle of the microchannel with a maximum deviation of ±5 μm from the center position. With the use of this system, a new approach for performing an immunoagglutination assay on-chip has been implemented. Three-dimensional focusing allowed reliable counting of singlets and agglutinated doublets. We demonstrate the potential of the agglutination assay in a microfluidic format using a streptasidin/biotinylated bovine serum albumin (bBSA) model system. A detection limit of about 400 pg/mL (6 pM) is achieved. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) is an emerging technology for desalination and water reuse. However, a big challenge is finding suitable draw solutes. In this work, we have synthesized magnetic nanoparticles (MNPs), investigated their potential as draw solutes in FO systems, and explored their recovery and reusability. A series of poly(ethylene glycol)diacid-coated (PEG−(COOH)2-coated) MNPs with different size distributions have been synthesized by means of the thermal decomposition method. The physical properties and chemical compositions of the resultant MNPs are fully characterized. Transmission electron microscopy (TEM) analyses show the characteristics of spherical morphology with narrow size distribution, and a mean size from 4.2 to 17.5 nm depending on the ratio of the two starting materials of PEG−(COOH)2to ferric triacetylacetonate (Fe(acac)3). Vibrating sample magnetometer analyses confirm the magnetic behavior of the PEG−(COOH)2MNPs. The PEG−(COOH)2layer on the MNPs ascertained from Fourier transform infrared (FTIR) analysis and thermogravimetric analysis demonstrates a hydrophilic surface composition. The as-prepared PEG−(COOH)2MNPs exhibit good dispersibility and generate high osmotic pressures in aqueous solutions. Water fluxes of >10 L m−2h−1are achieved across Hydration Technologies Inc. flat sheet membranes when deionized water is used as the feed solution. The MNPs can be easily recovered from draw solutions by applying a magnetic field. The MNPs remain active after nine runs of recycle but with a total water flux decrease of 21% due to slight aggregation. Results have demonstrated that using PEG−(COOH)2MNPs as draw solutes is feasible in the FO process. [ABSTRACT FROM AUTHOR]

Bactericidal paramagnetic particles were obtained either through the attachment of a conjugate of poly(ethyleneimine) (PEI) and poly(hexamethylene biguanide) (PHMBG) to the surface of magnetite (Fe3O4) particles, or via the sol-gel encapsulation of magnetite particles with a functional silane (3-glycidoxypropyl trimethoxysilane) and subsequent binding of the polysiloxane shell by the amine/imine groups of PHMBG. The encapsulated core-shell particles possess a high saturation magnetization, which is preserved for more than 10 months while in contact with air in aqueous suspensions. The minimum inhibitory concentration (MIC) of the encapsulated particles for eight types of bacteria was size-dependent, with polydisperse submillimeter particles possessing a several-fold higher MIC than analogous particles sized below 250 nm. The encapsulated particles are biocompatible and nontoxic to mammalian cells such as mouse fibroblasts. The particles efficiently bind both glycopeptide components mimicking the Gram-positive bacteria membranes and whole bacteria, and possess broad-range bactericidal activity. The cell-particle complexes can be captured, manipulated, and removed by means of a magnet. [ABSTRACT FROM AUTHOR]

A model paramagnetic nanoparticle (MNP) assay is demonstrated for surface-enhanced Raman scattering (SERS) detection of DNA oligonucleotides derived from the West Nile virus (WNV) genome. Detection is based on the capture of WNV target sequences by hybridization with complementary oligonucleotide probes covalently linked to fabricated MNPs and Raman reporter tagconjugated gold nanoparlicles (GNPs) and the subsequent removal of GNP-WNV target sequence-MNP hybridization complexes from solution by an externally applied magnetic source. Laser excitation of the pelleted material provided a signature SERS spectrum which is diagnostic for the reporter, 5,5'-dithiobis(succinimidy-2-nitrobenzoate) (DSNB), and restricted to hybridization reactions containing WNV target sequences. Hybridizations containing dilutions of the target oligonucleotide were characterbed by a reduction in the intensification of the spectral peaks accorded to the SERS signaling of DSNB, and the limit of detection for target sequence in buffer was 10 μM. Due to the short hybridization limes required to conduct the assay and ease with which reproducible Raman spectra can be acquired, the assay is amenable to adaptation within a portable, user-friendly Raman detection platfonn for nucleic acids. [ABSTRACT FROM AUTHOR]

Monte Carlo simulation results predicting the state of dispersion (single, dimer, trimer, and so on) of coated superparamagnetic iron oxide (Fe3O4) nanoparticles in an aqueous medium are compared with our experimental data for the same. Measured values of the volume percentage of particles in the dispersion, core particle diameter, coating-shell thickness, grafting density of the coating agent, saturation magnetization, and zeta potential for the citric acid-coated and poly(acrylic acid) [PAA]-coated particles have been used in our simulation. The simulation was performed by calculating the total interaction potential between two nanoparticles as a function of their interparticle distance and applying a criterion for the two particles to aggregate, with the criterion being that the minimum depth of the secondary minima in the total interaction potential must be at least equal to kBT. Simulation results successfully predicted both experimental trendsaggregates for citric acid-coated particles and an individual isolated state for PAA-coated particles. We have also investigated how this state changes for both kind of coating agents by varying the particle volume percentage from 0.01 to 25%, the particle diameter from 2 to 19 nm, the shell thickness from 1 to 14 nm, and grafting density from 1015to 1022molecules/m2. We find that the use of a lower shell thickness and a higher particle volume percentage leads to the formation of larger aggregates. The possible range of values of these four variables, which can be used experimentally to prepare a stable aqueous dispersion of isolated particles, is recommended on the basis of predictions from our simulation. [ABSTRACT FROM AUTHOR]

This study reports on the fabrication of magnetically responsive hollow titania capsules by confining the superparamagnetic Fe3O4nanoparticles within a hollow and porous titania (TiO2) shell. The employed protocol involves precipitation of titania shell on the magnetite (Fe3O4) encapsulated polystyrene beads followed by the calcination of resulting composite particles at elevated temperature. Scanning electron microscopy and transmission electron microscopy reveal the presence of a thick, complete but irregular titania shell on the magnetic polystyrene beads after the templating process. Electron energy loss mapping image analysis has been employed to investigate the spatial distribution of titania and magnetite phases of magnetic hollow titania capsules (MHTCs). Magnetic characterization indicates that both titania-coated magnetic polystyrene beads (TMPBs) and MHTCs are superparamagnetic in nature with the saturated magnetizations of 5.6 and 8.1 emu/g, respectively. X-ray diffraction (XRD) analysis reveals that titania shell of these capsules is composed of photoactive anatase phase. Nitrogen adsorption−desorption analysis has been employed to estimate the specific surface area and the average pore diameter of the fabricated hollow structures. Photocatalytic activity of the fabricated MHTCs for the photodegradation of rhodamine 6G dye has been demonstrated and compared with that of bulk titania nanoparticles. [ABSTRACT FROM AUTHOR]

A new method is presented for patterning surfaces with gradient properties. The method is based on magnetolithography in which the surface patterning is performed by applying a gradient of a magnetic field on the substrate, using paramagnetic metal masks in the presence of a constant magnetic field. Superparamagnetic nanoparticles (NPs) are deposited on the substrate, and they assemble according to the field and its gradients induced by the mask. Once they pattern the substrate, they protect their sites on the substrate from interacting with any other species. The areas not protected by the NPs can be covered by molecules that chemically bind to the substrate. After these molecules are bound, the NPs are removed, and other molecules may be adsorbed on the newly exposed area. The new technique is based on a parallel process that can be carried out on a full wafer. It provides high resolution, it creates gradient continuously from submicrometers to milimeters, and it can be performed on surfaces that are not flat and that are even on the inside of a tube. The gradient that is formed is not limited to a specific property or type of substrate. [ABSTRACT FROM AUTHOR]

Magnetite and metallic cobalt-based nanoparticles with sizes ranging from 10 to 300 nm and surface-functionalized with poly(hexamethylene biguanide) (PHMBG) are introduced as capable lipopolysaccharide (LPS)-sequestering agents. The nanoparticles efficiently bind to whole E. colicells and can be used to separate the cells effectively from suspension using a magnet. A fluorescence dye displacement assay shows strong affinities of the nanoparticles for lipid A, the glycolipid component of LPS responsible for septic shock. The particle−lipid A affinity is of the same order of magnitude or higher than that of polymyxin B. The affinity of smaller (100 nm) due to their higher surface area to volume ratio. The nanoparticles possess high saturation capacity for double-stranded λDNA from E. coli, with which particle−polyelectrolyte complexes are formed. The PHMBG-modified nanoparticles are potent bactericides, inhibiting E. coliviability and growth at concentrations at ≤10 μg/mL. [ABSTRACT FROM AUTHOR]

Three polarity-sensitive organic molecules (DIAA, DIUA, and DISA) were designed and synthesized for functionalizing high-quality superparamagnetic Fe3O4nanoparticles (NPs) via the ligand exchange strategy to prepare polarity-sensitive Fe3O4NPs. The functional group is chosen to be the carboxyl group (one for DIAA and DIUA, two for DISA) that is a universal coordinating site for iron oxide NPs. The method for binding these functional molecules onto the surface of the NPs is simple and straightforward. Among the three molecules, the DISA molecules passivate the NPs’ surface most efficiently owing to their particular structure with two carboxyl groups and a general good solubility. The DISA-functionalized Fe3O4NPs (DISA−Fe3O4NPs) display distinctly different fluorescence emissions in various solvents of different polarities with the magnetism well preserving. The prepared polarity-sensitive Fe3O4NPs that are dual functional can be used as a visualized polarity sensor and perform NPs’ superparamagnetic properties simultaneously. It also provides a conceptual design for preparing the polarity-sensitive nanomaterials with multifunction. [ABSTRACT FROM AUTHOR]

In this work, we report a robust wet-chemical route to synthesize monosized octahedron-shaped magnetite (Fe3O4) nanoparticles with average sizes ranging from 8 to ∼430 nm. In other words, we are able to adjust the magnetic properties of the as-synthesized nanoparticles from superparamagnetic to single-domain to multidomain ferrimagnetic regimes. We also demonstrate a simple solvent-evaporation assembly process to obtain either 2D monolayer or 3D microrod superstructures made of 21 nm-sized nanooctahedra by applying a weak magnetic field (∼0.06 T) in the horizontal or vertical direction, respectively. The as-obtained 2D monolayer assembly not only exhibits a long-range translational order (hexagonal close packing) but also has a high degree of crystallographic orientational order (⟨111⟩ texture normal to the substrate). Large-area assemblies (up to 10 × 10 μm) can be formed on various substrates, for example, silicon substrates and carbon films of transmission electron microscopy copper grids, as demonstrated. By changing the magnetic field to the vertical direction, uniform 3D microrod superstructures with an aspect ratio of approximately 5 are obtained, and they also exhibit the specific crystallographic orientations. [ABSTRACT FROM AUTHOR]

Superparamagnetic single crystal single domain Co nanoparticles of 6 nm in diameter evaporated onto highly pyrolytic oriented graphite spontaneously self-assemble into super structures with an elongated shape. These structures have been studied by optical and scanning electron microscopies, atomic and magnetic force microscopy, electron dispersive X-ray analysis, and SQUID magnetometry. We propose that the weak dipolar interactions between superparamagnetic dipoles of the cobalt nanoparticles are responsible for the formation of these structures when the dipolar magnetic interactions are strong enough to influence the general process of self-assembly dominated by van der Waals forces between neighboring nanoparticles and between nanoparticles and the substrate during evaporation of the solvent. [ABSTRACT FROM AUTHOR]

Nanoparticles with monodisperse, spherical magnetic iron oxide cores and contiguous gold shells (Fe/Au NPs) have been synthesized in order to combine magnetophoretic responsiveness and localized surface plasmon resonance in a single nanoparticle. Such particles are sufficiently charged to be stable against flocculation in low ionic strength media, but they require surface modification to be stably dispersed in elevated ionic strength media that are appropriate for biotechnological applications. Dynamic light scattering and ultraviolet−visible spectrophotometry are used to monitor the colloidal stability of Fe/Au NPs in pH 7.4 phosphate buffered saline containing 154 mM NaCl (PBS). While uncoated particles flocculate immediately upon introduction to PBS, Fe/Au NPs with adsorbed layers of bovine serum albumin or the amphiphilic triblock copolymers Pluronic F127 and Pluronic F68 resist flocculation after more than 5 days in PBS. Adsorbed dextran allowed flocculation that was limited to the formation of small clusters, while poly(ethylene glycol) homopolymers ranging in molecular weight from 6000 to 100 000 were ineffective steric stabilizers. The effectiveness of adsorbed Pluronic copolymers as steric stabilizers was interpreted in terms of the measured adsorbed layer thickness and extended Derjaguin−Landau−Verwey−Overbeek (DLVO) theory predictions of interparticle interactions. [ABSTRACT FROM AUTHOR]

Secondary structural, superparamagnetic Fe3O4microparticles with an average diameter of 280 nm have been successfully synthesized by using a one-step hydrothermal method. The size of the primary nanograins has been controlled from 5.9 to 21.5 nm by varying the sodium acrylate/sodium acetate weight ratios. The magnetic properties of the Fe3O4microparticles have been characterized at room temperature, whereas the saturation magnetization values of the Fe3O4microparticles increase with increasing grain sizes. Magnetic resonance imaging reveals that Fe3O4microparticle with larger grain size yields higher molar T2relaxation rate. A plausible growth mechanism of the particles is proposed, and the role of sodium acrylate and sodium acetate for tuning the grain size of the particles has been discussed. Additionally, the size of the secondary structural Fe3O4particles can also be continuously controlled from 6 to 170 nm by varying the volume ratio of ethylene glycol/diethylene glycol in a bisolvent system. The described method presents the synthesis of secondary structural nanomaterials with tunable sizes, grain sizes, and different magnetic responses. [ABSTRACT FROM AUTHOR]

Nanoparticles and their interaction with human cells have been a focus of many groups during the past decade. We discuss and review here the progress in the field of understanding and harnessing the interactions of polymeric nanoparticles synthesized by the miniemulsion process with different cell types. Nanotechnology and the hereby produced nanomaterials have promised to make use of specific properties of supramolecular assemblies and nanomaterials so that hitherto inaccessible effects can be exploited for new applications. Examples are superparamagnetism or the high surface area helpful for catalysis and adsorption. In biology and medicine, superparamagnetic iron oxide nanoparticles have been used for cell selection and as magnetic resonance imaging (MRI) contrast agents. Furthermore, uptake of nanoparticles into a wide variety of cells is an effect that seems to be specific for materials in the range of 50−200 nm. Surface modifications (positively or negatively charged side groups of the polymers, amino acids, or peptides/proteins) enhance this uptake. Knowledge about factors influencing cellular uptake, like size, surface properties, cell type, and endocytotic pathways, enables optimization of labeling and selection of cells and nanoparticles for applications in vitro and in vivo. For in vivo applications, we will focus on how nanoparticles can cross the blood−brain barrier. [ABSTRACT FROM AUTHOR]

Superparamagnetic nanoparticles were encapsulated in liposomes prior to the stepwise adsorption of polyelectrolytes of opposite charges commonly known as the layer-by-layer (LbL) technique. Magnetic fields allow a fast separation of coated liposomes from unbound polyelectrolytes. The coated particles were characterized by dynamic light scattering (DLS), cryo-TEM, AFM, and zeta-potential techniques. The presence of magnetic nanoparticles and the polyelectrolyte shell opens the possibility of their magnetic manipulation and targeting by applying an external magnetic or electric field. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles are frequently coated with SiO2to improve their functionality and biocompatibility in a range of biomedical and polymer nanocomposite applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coated with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis of iron acetylacetonate in xylene/acetonitrile solutions and the resulting aerosol was in situ coated with silicon dioxide by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3(maghemite) particle properties and the thickness of their silica coating film. This ensures that the nonmagnetic SiO2layer can be closely controlled and minimized. The optimal SiO2content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe2O3coated with about 2 nm thin SiO2layers was nearly identical to that of uncoated, pure Fe2O3nanoparticles. [ABSTRACT FROM AUTHOR]

Folic acid-functionalized Fe3O4nanoparticles (FA-Fe3O4NPs) were synthesized from iron(III) 3-allylacetylacetonate (IAA) through in situhydrolysis and ligand modification, by applying the principle of “click chemistry”. The γ-carboxylic acid of FA was successfully bound to the ligand of the Fe3O4NPs without the loss of the α-carboxylic acid group of folic acid (FA), which has an affinity for folate receptors (FRs) expressed on tumor cells. The Fe3O4NPs were monodisperse, and their size was controlled by varying the conditions of IAA hydrolysis. The FA-Fe3O4NPs, which had diameters of 8 nm, exhibited superparamagnetic behavior and a relatively high magnetization at room temperature. The blocking temperature was determined to be 220 K, and the magnetization curve exhibited a remanence of 19 emu/g and a coercivity of 550 Oe at 5 K. The specific absorption rate (SAR) was dependent on the size of the FA-Fe3O4NPs and the strength of the applied magnetic field. The SAR of the 8-nm FA-Fe3O4NPs was 670 W/g in a 230 kHz alternating magnetic field and 100 Oe. The chemoselective surface modification of magnetite particles with FA yielded a novel cancer-targeting system for use in hyperthermia treatment. [ABSTRACT FROM AUTHOR]

Superparamagnetic iron oxide nanoparticles (SPIONs) have been receiving great attention lately due to their various biomedical applications, such as in MR imaging and image guided drug delivery. However, their systemic administration still remains a challenge. In this study, the ability of biodegradable thermosensitive polymeric micelles to stably encapsulate hydrophobic oleic-acid-coated SPIONs (diameter 5−10 nm) was investigated, to result in a system fulfilling the requirements for systemic administration. The micelles were composed of amphiphilic, thermosensitive, and biodegradable block copolymers of poly(ethylene glycol)-b-poly[N-(2-hydroxypropyl) methacrylamide dilactate] (mPEG-b-p(HPMAm-Lac2)). The encapsulation was performed by addition of one volume of SPIONs in THF to nine volumes of a cold aqueous mPEG-b-p(HPMAm-Lac2) solution (0 °C; below the cloud point of the polymer), followed by rapid heating of the resulting mixture to 50 °C, to induce micelle formation (“rapid heating” procedure). Dynamic light scattering (DLS) measurements revealed that ∼200 nm particles (PDI = 0.2) were formed, while transmission electron microscopy (TEM) analysis demonstrated that clusters of SPIONs were present in the core of the micelles. A maximum loading of 40% was obtained, while magnetic resonance imaging (MRI) scanning of the samples demonstrated that the SPION-loaded micelles had high r2and r2* relaxivities. Furthermore, the r2* values were found to be at least 2-fold higher than the r2values, confirming the clustering of the SPIONs in the micellar core. The particles showed excellent stability under physiological conditions for 7 days, even in the presence of fetal bovine serum. This, together with their ease of preparation and their size of ∼200 nm, makes these systems highly suitable for image-guided drug delivery. [ABSTRACT FROM AUTHOR]

A method for isolating single crystalline sub-5 nm carbon coated iron nanoparticles (Fe@C NPs) from a carbon nanotube matrix has been developed. The isolation of such particles allows for their characterization by high resolution electron microscopy methods and SQUID magnetometry. While the NPs are superparamagnetic at room temperature, at 10 K they exhibit a coercivity nearly 30 times greater than that of commercial Fe 3O 4NPs of comparable size. A novel nanotemplate directed assembly method for manipulating the particles at the individual particle level is also reported. [ABSTRACT FROM AUTHOR]

Abstract: A major challenge in magnetic nanoparticle synthesis and (bio)functionalization concerns the precise characterization of the nanoparticle surface ligands. We report the first analytical NMR investigation of organic ligands stably anchored on the surface of superparamagnetic nanoparticles (MNP5) through the development of a new experimental application of high-resolution magic-angle spinning (HRMAS). The conceptual advance here is that the HRMAS technique, already being used for MAS NMR analysis of gels and semisolid matrixes, enables the fine-structure-resolved characterization of even complex organic molecules bound to paramagnetic nanocrystals, such as nanosized iron oxides, by strongly decreasing the effects of paramagnetic disturbances. This method led to detail-rich, well-resolved 1H NMR spectra, often with highly structured first-order couplings, essential in the interpretation of the data. This HRMAS application was first evaluated and optimized using simple ligands widely used as surfactants in MNP synthesis and conjugation. Next, the methodology was assessed through the structure determination of complex molecular architectures, such as those involved in MNP3 and MNP4. The comparison with conventional probes evidences that HRMAS makes it possible to work with considerably higher concentrations, thus avoiding the loss of structural information. Consistent 2D homonuclear 1H-1H and 1H-13C heteronuclear single-quantum coherence correlation spectra were also obtained, providing reliable elements on proton signal assignments and carbon characterization and opening the way to 13C NMR determination. Notably, combining the experimental evidence from HRMAS 1H NMR and diffusion-ordered spectroscopy performed on the hybrid nanoparticle dispersion confirmed that the ligands were tightly bound to the particle surface when they were dispersed in a ligand-free solvent, while they rapidly exchanged when an excess of free ligand was present in solution. In addition to HRMAS NMR, matrix-assisted laser desorption ionization time-of-flight MS analysis of modified MNPs proved very valuable in ligand mass identification, thus giving a sound support to NMR characterization achievements. [ABSTRACT FROM AUTHOR]

A magnetically separable palladium catalyst was simply synthesized through a wet impregnation incorporating palladium nanoparticles and superparamagnetic Fe 3O 4nanoparticles in KBH 4solution, which is a highly efficient catalyst for the carbonylative Sonogashira coupling reaction of aryl iodides with terminal alkynes under phosphine-free conditions. This catalyst is completely magnetically recoverable due to the super paramagnetic behavior of Fe 3O 4and can be reused with sustained selectivity and activity. [ABSTRACT FROM AUTHOR]

The transverse ¹H relaxivities of aqueous colloidal solutions of dextran coated Dy2O3 nanoparticles of different sizes were investigated at magnetic field strengths (B) between 7 and 17.6 T. The particle size with the maximum relaxivity (r2) appears to vary between 70 nm at 7 T (r2 ≈190 s-1 mM-1) and 60 nm at 17.6 T (r2 ≈ 675 s-1 mM-1). A small difference between r2 and r2* was observed, which was ascribed to the effect of the dextran coating. The value of r2 is proportional to B² up to 12 T after which it saturates. Independent magnetization measurements on these particles at room temperature at magnetic field strengths up to 30 T, however, show a typical paramagnetic behavior with a magnetization of the particle that is proportional to the field strength. The saturation in the curve of r2 as a function of B² was tentatively explained by the presence of an extremely fast relaxing component of the signal at high field strengths, which is not observable on the NMR time scale. The results of this Study can be exploited for the rational design of MRI contrast agents, based on lanthanide oxide particles, with high efficiencies at magnetic field strengths of more than 1.5 T. [ABSTRACT FROM AUTHOR]

We report the fabrication and characterization of antifouling polymer-coated magnetic nanoparticles as nanoprobes for magnetic resonance (MR) contrast agents. Magnetite superparamagnetic iron oxide nanoparticles (SPION) were coated with the protein- or cell-resistant polymer, poly(TMSMA-r-PEGMA), to generate stable, protein-resistant MR probes. Coated magnetic nanoparticles synthesized using two different preparation methods (in situ and stepwise, respectively) were both well dispersed in PBS buffer at a variety of pH conditions (pH 1 -10). In addition, dynamic light scattering data revealed that their sizes were not altered even after 24 h of incubation in 10% serum containing cell culture medium, indicative of a lack of protein adsorption on their surfaces. When the antibiofouling polymer-coated SPION were incubated with macrophage cells, uptake was significantly lower in comparison to that of the popular contrast agent, Feridex IV., suggesting that the polymer-coated SPION can be long-circulated in plasma by escaping from uptake by the reticular endothelial system (RES) such as macrophages. Indeed, when the coated SPION were administered to tumor xenograft mice by intravenous injection, the tumor could be detected in 12-weighted MR images within 1 h as a result of the accumulation of the nanomagnets within the tumor site. Although the poly(TMSMA-r-PEGMA)-coated SPION do not have any targeting ligands on their surface, they are potentially useful for cancer diagnosis in vivo. [ABSTRACT FROM AUTHOR]

We present a simple model to describe the induction of magnetic behavior on gold clusters upon chemisorption of one organic molecule with different chemical linkers. In particular, we address the problem of stability of the lowest lying singlet and show that for some linkers there exists a spin symmetry-breaking that lowers the energy and leads to preferential spin density localization on the gold atoms neighboring the chemisorption site. The model is basically an adaptation of the Stoner model for itinerant electron ferromagnetism to finite clusters and it may have important implications for our understanding of surface magnetism in larger nanosystems and its relevance to electronic transport in electrode−molecule interfaces. [ABSTRACT FROM AUTHOR]

The structure, magnetism, and phase transition of core-shell type CoPt nanoparticles en route to solid solution alloy nanostructures are systematically investigated. The characterization of COcorePtshell nanoparticles obtained by a "redox transmetalation" process by transmission electron microscopy (TEM) and, in particular, X-ray absorption spectroscopy (XAS) provides clear evidence for the existence of a core-shell type bimetallic interlacial structure. Nanoscale phase transitions of the COcorePtshell structures toward c-axis compressed face-centered tetragonal (fct) solid solution alloy CoPt nanoparticles are monitored at various stages of a thermally induced annealing process and the obtained fct nanoalloys show a large enhancement of their magnetic properties with ferromagnetism. The relationship between the nanostructures and their magnetic properties is in part elucidated through the use of XAS as a critical analytical tool. [ABSTRACT FROM AUTHOR]

Reports that a correlation between the electron spin-orbital angular momentum coupling and the superparamagnetic properties has been established in MgFe2O4 and CoFe2O4 spinel ferrite nanoparticles. Contribution of the magnetic anisotropy from the Fe3+ lattice sites; Neutron diffraction studies.

We have successfully prepared a series of magnetically separable "quasi-homogeneous" Pd-Ni nanoalloy catalysts with tunable composition in a one-pot wet chemical route. We have evaluated the catalytic activity of these Pd-Ni alloy catalysts with different compositions through the Miyaura-Suzuki coupling reaction. These palladium/non-noble metal alloy catalysts show better catalytic activity than an equal amount of palladium nanoparticles. Furthermore, these catalysts exhibited excellent performance in superparamagnetism owing to its great advantage for reducing the usage of noble metal. [ABSTRACT FROM AUTHOR]

The functionalization of superparamagnetic iron oxide nanoparticles (SPIOs) by meso-2,3-dimercaptosuccinic acid (DMSA) was investigated. Under ambient conditions, the thiol groups from DMSA are not stable and do not allow a direct functionalization without storage in stringent conditions or a chemical regeneration of free thiols. In this study, we have developed a protocol based on poly(ethylene glycol) (PEG) grafting of SPIO prior to DMSA anchoring. We have observed that PEG helps to increase the stability of thiol groups under ambient conditions. The thiol functionalized SPIOs were stable under physiological pH and ionic strength as determined by Ellman’s essay and allowed us to graft a thiol reactive fluorescent dye: tetramethylrhodamine-5-maleimide (TMRM). [ABSTRACT FROM AUTHOR]

The article presents a study which reports on the reversible switching of paramagnetism of gold nanoparticle system consisting of truly monodisperse nanoparticles with 25 gold atoms stabilized by 18 thiolate ligands. The origin of the magnetism was successfully explained using the density dunctional theory (DFT) calculations. Study shows that the unpaired spin in the Au25(SR)18 nanoparticle resides in the Kohn-Sham highest occupied molecular orbital (HOMO).

The grafting of a monolayer of 6 nm superparamagnetic cyanide-bridged CsNiCr nanoparticles was achieved on a Ni(II)-functionalized Si(100) substrate; magnetic studies reveals that the grafted nanoparticles are nearly magnetically isolated within the monolayer. [ABSTRACT FROM AUTHOR]

The article describes the initial evidence of photoinduced superparamagnetism in 3 nm CuNiMo(CN)8 trimetallic coordination nanoparticles (CNP). The growth of the coordination network was confined using organic polymer polyvinyl pyrrolidone. The organic polymer also stabilized the nanoparticles. The trimetallic CNP features quantum magnetic tunneling at low temperature as observed in single-molecule magnets.

Examines the self-assembly of magnetic light modulators from exfoliated perovskite and magnetite nanoparticles. Synthesis of the nanostructure particles; Identification of the birefringence and light-scattering properties of nanoparticle; Superparamagnetism of the magnetite particles.

The article discusses the development of biotechnology nanoworms used to image tumor cells. The nanoworms consist of about 10 dextran-coated nanospheres of iron oxide which are superparamagnetic. The elongated nanostructures accumulated in the tumor cells and remained longer than nanospheres. The research was directed by Michael Sailor’s group at the University of California San Diego in collaboration with the Massachusetts Institute of Technology and the University of California at Santa Barbara. The research is published in the vol. 20, 2008 issue of “Advanced Materials.”