Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process

Nickel ferrite aerogels with monodisperse nanoscale building blocks--the importance of processing temperature and atmosphere

Using two-step (air/argon) thermal processing, sol-gel-derived nickel-iron oxide aerogels are transformed into monodisperse, networked nanocrystalline magnetic oxides of NiFe(2)O(4) with particle diameters that can be ripened with increasing temperature under argon to 4.6, 6.4, and 8.8 nm. Processing in air alone yields poorly crystalline materials; heating in argon alone leads to single phase, but diversiform, polydisperse NiFe(2)O(4), which hampers interpretation of the magnetic properties of the nanoarchitectures. The two-step method yields an improved model system to study magnetic effects as a function of size on the nanoscale while maintaining the particles within the size regime of single domain magnets, as networked building blocks, not agglomerates, and without stabilizing ligands capping the surface.

Bis-phosphonates-ultra small superparamagnetic iron oxide nanoparticles: a platform towards diagnosis and therapy

A new type of multifunctional magnetic nano-platform for diagnosis and therapy applications was designed using bisphosphonate/carboxylic ligands.

Monodisperse α-Fe(2)O(3)@SiO(2)@Au core/shell nanocomposite spheres: synthesis, characterization and properties

A new hybrid spherical structure α-Fe(2)O(3)@SiO(2)@Au with a size of about 141 nm was designed, with a hematite cubic core surrounded by a thick silica shell and further decorated with gold nanoparticles. The monodisperse α-Fe(2)O(3)@SiO(2) spheres were first prepared by a sol-gel process based on the modified Stöber method. Subsequently, the surface of the α-Fe(2)O(3)@SiO(2) particles was functionalized by-NH(2) functional groups. The electrostatic attraction of -NH(2) groups will attach the negatively charged Au nanoparticles to the amino-functionalized α-Fe(2)O(3)@SiO(2) nanospheres in order to prepare α-Fe(2)O(3)@SiO(2) monodisperse hybrid spheres. The M(H) hysteresis loop for α-Fe(2)O(3)@SiO(2) and α-Fe(2)O(3)@SiO(2)@Au spheres indicates that the nanocomposite spheres exhibit superparamagnetic characteristics at room temperature. The optical properties and the application of these hybrid nanocomposites as catalysts for the conversion of CO to CO(2) have also been studied.

Monodisperse magnetite nanoparticles coupled with nuclear localization signal peptide for cell-nucleus targeting

Functionalization of monodisperse superparamagnetic magnetite (Fe(3)O(4)) nanoparticles for cell specific targeting is crucial for cancer diagnostics and therapeutics. Targeted magnetic nanoparticles can be used to enhance the tissue contrast in magnetic resonance imaging (MRI), to improve the efficiency in anticancer drug delivery, and to eliminate tumor cells by magnetic fluid hyperthermia. Herein we report the nucleus-targeting Fe(3)O(4) nanoparticles functionalized with protein and nuclear localization signal (NLS) peptide. These NLS-coated nanoparticles were introduced into the HeLa cell cytoplasm and nucleus, where the particles were monodispersed and non-aggregated. The success of labeling was examined and identified by fluorescence microscopy and MRI. The work demonstrates that monodisperse magnetic nanoparticles can be readily functionalized and stabilized for potential diagnostic and therapeutic applications.

One-step solid state synthesis of capped γ-Fe(2)O(3) nanocrystallites

The thermally induced solid state synthesis of soluble organophilic maghemite (γ-Fe(2)O(3)) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt state of Fe(NO)(3)·9H(2)O and RCOOH (R = C(11)H(23), C(15)H(31)) at 240 °C. The method yields well-crystallized nanoparticles of γ-Fe(2)O(3) functionalized with the corresponding aliphatic acid. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations reveal composite particles with faceted magnetic cores and average size of 20 nm, which are well capped with the surrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermal analysis suggest a bimodal configuration of the organic shell including chemically coordinated and physisorbed molecules of aliphatic acid. The chemical bonding of the carboxylate groups to the surface iron atoms is also indicated by a paramagnetic doublet with unchanged area in the variable temperature Mössbauer spectra. The spinel γ-Fe(2)O(3) particles exhibit perfect structural and magnetic ordering, including the almost ideal ratio of octahedral to tetrahedral positions (5/3) and very low degree of spin canting, as confirmed by in-field Mössbauer spectroscopy. Magnetic measurements demonstrate the suitable properties required in various (bio)magnetic applications like superparamagnetic behavior at room temperature, high saturation magnetization achievable at low applied fields and suppressed magnetic interactions.

Design and synthesis of novel magnetic core-shell polymeric particles

A novel synthetic strategy was developed for the preparation of magnetic core-shell (MCS) particles consisting of hydrophobic poly(methyl methacrylate) cores with hydrophilic chitosan shells and gamma-Fe2O3 nanoparticles inside the cores via copolymerization of methyl methacrylate from chitosan in the presence of vinyl-coated gamma-Fe2O3 nanoparticles. The magnetic core-shell particles were characterized with transmission electron microscopy, field-emission scanning electron microscopy, particle size and zeta-potential measurements, vibrating sample magnetometry, and atomic force microscopy, respectively. The MCS particles were less than 200 nm in diameter with a narrow size distribution (polydispersity = 1.09) and had a good colloidal stability (critical coagulation concentration = 1.2 M NaCl at pH 6.0). Magnetization study of the particles indicated that they exhibited superparamagnetism at room temperature and had a saturation magnetization of 2.7 A m2/kg. The MCS particles were able to form a continuous film on a glass substrate, where magnetic nanoparticles could evenly disperse throughout the film. Thus, these new materials should be extremely useful in various applications.

Magnetic resonance imaging of major histocompatibility class II expression in the renal medulla using immunotargeted superparamagnetic iron oxide nanoparticles

We demonstrate the development and successful application of immunotargeted superparamagnetic iron oxide nanoparticles (ITSIONs), with in vivo magnetic resonance diagnostic and potential drug delivery capability for kidney disease. Further, the versatility of the conjugation chemistry presents an attractive route to the preparation of a range of biomolecule-nanoparticle conjugates. The ITSION contrast agent is a stable, biocompatible, targeted nanoparticle complex that combines a monodisperse iron oxide nanoparticle core with a functionalized phospholipid coating conjugated to antibodies that is capable of targeting normal cells expressing specific target antigens. The plasma half-life and R1 and R2 relaxivities suggest sufficient time for targeted binding while clearing from the system quick enough for detection of specific contrast enhancement. RT1 anti-MHC Class II antibodies were used to target the renal medulla of the rat, a section of the kidney in which MHC Class II, associated with inflammation, is specifically expressed. For in vivo resonance imaging, we compare phospholipid coated nanoparticles, nonspecific ITSIONs, and RT1 ITSIONs. Enhanced binding of the RT1 ITSIONS indicates specificity for the renal medulla and thus potential for disease detection or drug delivery.

Sonochemical synthesis of amorphous nanoscopic iron(III) oxide from Fe(acac)3

Amorphous nanoscopic iron(III) oxide with interesting magnetic properties was prepared by sonolysis of Fe(acac)(3) under Ar in tetraglyme with a small amount of added water. The organics content and the surface area of the Fe(2)O(3) nanoparticles can be controlled with an amount of water in the reaction mixture and it increases from 48 m(2)g(-1) for dry solvent up to 260 m(2)g(-1) when wet Ar is employed. For further monitoring of the particle size and morphology and for the study of the surface, magnetic and thermal properties, the sample with 2 vol.% of H(2)O was chosen. SEM showed nanoscopic composite particles of a uniform size distribution and nearly spherical shapes with an estimated diameter of 20 nm. Such composites are built from amorphous iron(III) oxide nanoparticles (3 nm) embedded in an acetate matrix as proved by TEM and IR spectroscopy. Temperature-dependent Mössbauer spectra demonstrate a very narrow magnetic transition with an unusually low transition temperature around 25K reflecting the system of magnetically non-interacting ultrasmall particles with a narrow size distribution. The in-field (5T) Mössbauer spectrum recorded at 5K shows a minimum change compared to the zero-field spectrum indicating an absence of the long-range magnetic ordering. The composite particles are thermally stable up to 150 degrees C, which is confirmed by DSC, TG, and by the constant surface area. At higher temperatures, acetate groups are removed from the particle surface, which is documented by the increased surface area and disappearance of their IR bands.

Controlling transport and chemical functionality of magnetic nanoparticles

A wide range of metal, magnetic, semiconductor, and polymer nanoparticles with tunable sizes and properties can be synthesized by wet-chemical techniques. Magnetic nanoparticles are particularly attractive because their inherent superparamagnetic properties make them desirable for medical imaging, magnetic field assisted transport, and separations and analyses. With such applications on the horizon, synthetic routes for quickly and reliably rendering magnetic nanoparticle surfaces chemically functional have become an increasingly important focus. This Account describes common synthetic routes for making and functionalizing magnetic nanoparticles and discusses initial applications in magnetic field induced separations. The most widely studied magnetic nanoparticles are iron oxide (Fe2O3 and Fe3O4), cobalt ferrite (CoFe 2O4), iron platinum (FePt), and manganese ferrite (MnFe 2O4), although others have been investigated. Magnetic nanoparticles are typically prepared under either high-temperature organic phase or aqueous conditions, producing particles with surfaces that are stabilized by attached surfactants or associated ions. Although it requires more specialized glassware, high-temperature routes are generally preferred when a high degree of stability and low particle size dispersity is desired. Particles can be further modified with a secondary metal or polymer to create core-shell structures. The outer shells function as protective layers for the inner metal cores and alter the surface chemistry to enable postsynthetic modification of the surfactant chemistry. Efforts by our group as well as others have centered on pathways to yield nanoparticles with surfaces that are both easily functionalized and tunable in terms of the number and variety of attached species. Ligand place-exchange reactions have been shown quite successful for exchanging silanes, acids, thiols, and dopamine ligands onto the surfaces of some magnetic particles. Poly(ethylene oxide)-modified phospholipids can be inserted into nonpolar surface monolayers of as-prepared nanoparticles as a method for modifying the surface chemistry that induces water solubility. In general, reactive termini can subsequently be used to append a range of chemical groups. For example, surfactants with trifluoroethylester or azide termini have been used to attach a range of amine- or alkyne-containing species, respectively. Chemically functionalized magnetic nanoparticles are promising as advanced materials for analytical separations and analysis. Magnetic field flow fractionation leverages the size-dependent magnetic moments to purify and separate the components of a complex mixture of particles. Similarly, magnetic field gradients are useful for manipulating transport and separation in simple microfluidic devices. By either approach, magnet-induced transport of the particles is a simple method in which an attached reagent, catalyst, or bioanalytical tag can be moved between flow streams within a lab on a chip device.

Solvothermal synthesis of well-dispersed MF(2) (M = Ca,Sr,Ba) nanocrystals and their optical properties

MF(2) (M = Ca,Sr,Ba) nanocrystals (NCs) were synthesized via a solvothermal process in the presence of oleic acid and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, UV/vis absorption spectra, photoluminescence (PL) excitation and emission spectra, and lifetimes, respectively. In the synthetic process, oleic acid as a surfactant played a crucial role in confining the growth and solubility of the MF(2) NCs. The as-prepared CaF(2), SrF(2) and BaF(2) NCs present morphologies of truncated octahedron, cube and sheet in a narrow distribution, respectively. Possible growth mechanisms were proposed to explain these results. The as-prepared NCs are highly crystalline and can be well dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrate strong emission bands centred at 400 nm in photoluminescence (PL) spectra compared with the cyclohexane solvent. The PL properties of the colloidal solutions of the as-prepared NCs can be ascribed to the trap states of surface defects.

One-pot synthesis and characterization of size-controlled bimagnetic FePt-iron oxide heterodimer nanocrystals

A one-pot, two-step colloidal strategy to prepare bimagnetic hybrid nanocrystals (HNCs), comprising size-tuned fcc FePt and inverse spinel cubic iron oxide domains epitaxially arranged in a heterodimer configuration, is described. The HNCs have been synthesized in a unique surfactant environment by temperature-driven sequential reactions, involving the homogeneous nucleation of FePt seeds and the subsequent heterogeneous growth of iron oxide. This self-regulated mechanism offers high versatility in the control of the geometric features of the resulting heterostructures, circumventing the use of more elaborate seeded growth techniques. It has been found that, as a consequence of the exchange coupling between the two materials, the HNCs exhibit tunable single-phase-like magnetic behavior, distinct from that of their individual components. In addition, the potential of the heterodimers as effective contrast agents for magnetic resonance imaging techniques has been examined.

Magnetic nanoparticles for gene and drug delivery

Investigations of magnetic micro- and nanoparticles for targeted drug delivery began over 30 years ago. Since that time, major progress has been made in particle design and synthesis techniques, however, very few clinical trials have taken place. Here we review advances in magnetic nanoparticle design, in vitro and animal experiments with magnetic nanoparticle-based drug and gene delivery, and clinical trials of drug targeting.

Functionalization of magnetic nanoparticles with organic molecules: Loading level determination and evaluation of linker length effect on immobilization

A general method is introduced to immobilize organic molecules on magnetic nanoparticles through silanization reactions and determine the maximum loading level by UV-vis spectroscopy. Loading levels of 1.5 x 10(-3) mol per gram of nanoparticle were obtained with structurally diverse compounds such as rhodamine B and glucosamine. The length of the linker did not have a significant effect on loading as comparable maximum amounts of rhodamine B were immobilized on magnetic nanoparticles regardless of the linker length. Interestingly, rhodamine B derivatives lost conjugation during synthetic manipulations due to reversible spiroisobenzofuran formation. Full regeneration of conjugation was found to be slow with rhodamine B attached on magnetic nanoparticles. The results obtained from these studies will be useful for studying surface functionalization of MNPs in general.

Simple synthesis of functionalized superparamagnetic magnetite/silica core/shell nanoparticles and their application as magnetically separable high-performance biocatalysts

Uniformly sized silica-coated magnetic nanoparticles (magnetite@silica) are synthesized in a simple one-pot process using reverse micelles as nanoreactors. The core diameter of the magnetic nanoparticles is easily controlled by adjusting the w value ([polar solvent]/[surfactant]) in the reverse-micelle solution, and the thickness of the silica shell is easily controlled by varying the amount of tetraethyl orthosilicate added after the synthesis of the magnetite cores. Several grams of monodisperse magnetite@silica nanoparticles can be synthesized without going through any size-selection process. When crosslinked enzyme molecules form clusters on the surfaces of the magnetite@silica nanoparticles, the resulting hybrid composites are magnetically separable, highly active, and stable under harsh shaking conditions for more than 15 days. Conversely, covalently attached enzymes on the surface of the magnetite@silica nanoparticles are deactivated under the same conditions.

A facile synthesis to Zn2SiO4:Mn2+ phosphor with controllable size and morphology at low temperature

Sphere- and rod-shaped Zn(2)SiO(4):Mn(2+) phosphor nanocrystals were synthesized at 230 degrees C. The process consists of tuning the surfactant concentration in the oil/surfactant/ethanol system. Powder X-ray (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, size and morphology. Photoluminescent (PL) spectra were collected and analyzed. Fourier transform infrared (FT-IR) spectra of the samples indicate the removal of surfactant in the phosphor nanoparticles. As a result, the sphere-shaped phosphor nanoparticles of 100 nm in size can be redispersed in ethanol ultrasonically. The suspension maintain stable for over 48 h.

Kinetics of Monodisperse Iron Oxide Nanocrystal Formation by “Heating-Up” Process

We studied the kinetics of the formation of iron oxide nanocrystals obtained from the solution-phase thermal decomposition of iron-oleate complex via the "heating-up" process. To obtain detailed information on the thermal decomposition process and the formation of iron oxide nanocrystals in the solution, we performed a thermogravimetric-mass spectrometric analysis (TG-MS) and in-situ magnetic measurements using SQUID. The TG-MS results showed that iron-oleate complex was decomposed at around 320 degrees C. The in-situ SQUID data revealed that the thermal decomposition of iron-oleate complex generates intermediate species, which seem to act as monomers for the iron oxide nanocrystals. Extensive studies on the nucleation and growth process using size exclusion chromatography, the crystallization yield data, and TEM showed that the sudden increase in the number concentration of the nanocrystals (burst of nucleation) is followed by the rapid narrowing of the size distribution (size focusing). We constructed a theoretical model to describe the "heating-up" process and performed a numerical simulation. The simulation results matched well with the experimental data, and furthermore they are well fitted to the well-known LaMer model that is characterized by the burst of nucleation and the separation of nucleation and growth under continuous monomer supply condition. Through this theoretical work, we showed that the "heating-up" and "hot injection" processes could be understood within the same theoretical framework in which they share the characteristics of nucleation and growth stages.

A general approach for transferring hydrophobic nanocrystals into water

Hydrophobic inorganic nanocrystals have been transferred from organic solvent to aqueous solution through a robust and general ligand exchange procedure. Polyelectrolytes such as poly(acrylic acid) and poly(allylamine) are used to replace the original hydrophobic ligands on the surface of nanocrystals at an elevated temperature in a glycol solvent and eventually render the nanocrystals highly water soluble. The physical properties of the nanocrystals, such as superparamagnetism, photocatalytic activity, and photoluminescence, are maintained or improved after ligand exchange.

Formation of protein-metal oxide nanostructures by the sonochemical method: observation of nanofibers and nanoneedles

The sonochemical reaction of iron pentacarbonyl is explored in water and in water with the protein BSA (bovine serum albumen). In water, the reaction is found to produce spherical nanoparticles of magnetite (Fe3O4) with a particle size distribution of <10 to approximately 60 nm. In water with BSA, the reaction produces either nanofibers or nanoneedles, depending on the concentration of BSA. The nanofiber and nanoneedle samples are found to be mixtures of goethite, lepidocrocite, and hematite (alpha-FeOOH, gamma-FeOOH, and alpha-Fe2O3, respectively). The sonochemical reaction of iron pentacarbonyl with BSA in water is thought to proceed through the thermal decomposition mechanism for iron pentacarbonyl with BSA acting as a templating agent.

Ultrasensitive detection and molecular imaging with magnetic nanoparticles

Recent advances in nanotechnology have produced a variety of nanoparticles ranging from semiconductor quantum dots (QDs), magnetic nanoparticles (MNPs), metallic nanoparticles, to polymeric nanoparticles. Their unique electronic, magnetic, and optical properties have enabled a broad spectrum of biomedical applications such as ultrasensitive detection, medical imaging, and specific therapeutics. MNPs made from iron oxide, in particular, have attracted extensive interest and have already been used in clinical studies owing to their capability of deep-tissue imaging, non-immunogenesis, and low toxicity. In this Research Highlight article, we attempt to highlight the recent breakthroughs in MNP synthesis based on a non-hydrolytic approach, nanoparticle (NP) surface engineering, their unique structural and magnetic properties, and current applications in ultrasensitive detection and imaging with a special focus on innovative bioassays. We will also discuss our perspectives on future research directions.

Iron phosphide nanostructures produced from a single-source organometallic precursor: nanorods, bundles, crosses, and spherulites

Single-source molecular precursors were found to produce iron phosphide materials. In a surfactant system of trioctylamine and oleic acid, H2Fe3(CO)9PtBu reacted to form Fe4(CO)12(PtBu)2, which decomposed to give Fe2P nanorods and "bundles." Control of the morphology obtained was possible by varying the surfactant system; addition of increasing amounts of oleic acid resulted in crystal splitting, while the addition of microliter amounts of an alkane enhanced the crystal splitting to give sheaflike structures. The different morphologies seen were attributed to imperfect crystal growth mechanisms.

Formation of Monodisperse and Shape-Controlled MnO Nanocrystals in Non-Injection Synthesis: Self-Focusing via Ripening

Formation of nearly monodiperse MnO nanocrystals by simple heating of Mn stearate in octadecene was studied systematically and quantitatively as a model for non-injection synthesis of nanocrystals. For controlling the shape of the nanocrystals, that is, rice, rods, peanuts, needles, and dots, either an activation reagent (ocadecanol) or an inhibitor (stearic acid) might be added prior to heating. The quantitative results of this typical non-injection system reveal that the formation of nearly monodisperse nanocrystals did not follow the well-known "focusing of size distribution" mechanism. A new growth mechanism, self-focusing enabled by inter-particle diffusion, is proposed. Different from the traditional "focusing of size distribution", self-focusing not only affects the growth process of the nanocrystals, but may also play a role in controlling nucleation. Because of the simplicity of the reaction system, it was possible to also identify the chemical reactions associated with the growth and ripening of MnO nanocrystals with a variety of shapes. Through a recycling reaction path, water was identified as a decisive component in determining the kinetics for both growth and ripening in this system, although the reaction occurred at around 300 degrees C.

One-Step Synthesis of Highly Water-Soluble Magnetite Colloidal Nanocrystals

A high-temperature solution-phase hydrolysis approach has been developed for the synthesis of colloidal magnetite nanocrystals with well-controlled size and size distribution, high crystallinity, and high water solubility. The synthesis was accomplished by the hydrolysis and reduction of iron(III) cations in diethylene glycol with a rapidly injected solution of sodium hydroxide at an elevated temperature. The high reaction temperature allows for control over size and size distribution and yields highly crystalline products. The superior water solubility is achieved by using a polyelectrolyte, that is, poly(acrylic acid) as the capping agent, the carboxylate groups of which partially bind to the nanocrystal surface and partially extend into the surrounding water. The direct synthesis of water-soluble nanocrystals eliminates the need for additional surface modification steps which are usually required for treating hydrophobic nanocrystals produced in nonpolar solvents through the widely recognized pyrolysis route. The abundant carboxylate groups on the nanocrystal surface allow further modifications, such as bioconjugation, as demonstrated by linking cysteamine to the particle surface. The monodisperse, highly water-soluble, superparamagnetic, and biocompatible magnetite nanocrystals should find immediate important biomedical applications.

Transparent CoAl2O4 Hybrid Nano Pigment by Organic Ligand-Assisted Supercritical Water

Transparent types of inorganic pigments are important as they can be used in a variety of applications, such as metallic finishing, contrast enhancing luminescent pigments, high-end optical filters, and so on. Currently, the difficulty in producing monodisperse and stable binary metal oxide nano pigments at low temperature hampers the applicability and realization of transparent blue nano pigments. Here, for the first time, we report organic ligand capped CoAl2O4 hybrid transparent nano pigment, which has a particle size less than 8 nm with well-stabilized single nanocrystals, using organic ligand-assisted supercritical water as the reaction medium. The organic ligand capping could effectively inhibit the particle growth and also control the size of nanocrystals. This helps to diminish the scattering effect of the nano blue pigment, realizing a transparent cobalt blue nano pigment without any postheat treatment.