Spherical Magnetite Nanoparticles Research Articles

Direct synthesis of ultrasmall and stable magnetite nanoparticles coated with one single carbon layer for sensitive surface-enhanced Raman scattering

Ultrasmall spherical magnetite nanoparticles (Fe3O4 NPs) coated with one single carbon layer (Fe3O4@1C NPs) were directly synthesized by a simple, fast one-step hydrothermal reaction at low temperature (200 °C). The as-synthesized Fe3O4@1C NPs were easily separated and purified from the resultant mixture, without the need for any additional energy input and chemicals. The as-purified Fe3O4@1C NPs not only displayed typical superparamagnetic behavior but also exhibited quite good long-term stability after being exposed to the open air under the room conditions for more than 2 months. Importantly, the long-term stored Fe3O4@1C NPs exhibited a highly sensitive surface-enhanced Raman spectroscopy (SERS) response toward Rhodamine-B (RdB) molecules with low concentration. The multifunctional and recyclable Fe3O4@1C NPs presented a prospective application for the selective enrichment and sensitive SERS detection of chemical and biomolecular assays.

Influence of solution pH on the formation of iron oxide nanoparticles

Iron oxide phase orientation were highly influenced by solution pH, crystalline structure, purity, surface enrichment, particle size, and morphology. This paper investigates the influence of pH changes by varying the precursor anions of chloride (FeCl2) and sulphate (FeSO4) on the formation of iron oxide nanoparticles using one step controlled precipitation technique. The obtained titration curve provided vital information on the reaction mechanism whereby different hydrolysis rate of precursor leads to different iron oxide phases. It was determined that at pH 4, goethite (α-FeOOH) was obtained. Continuous addition of hydroxyl ions (OH−) then forms iron hydroxides (Fe(OH)2) which will then subsequently react with the goethite precipitating magnetite (Fe3O4) nanoparticles (35–45 nm) at pH 10 with ferromagnetic behavior. By the use of Cl− anion, the slower hydrolysis process induced requires more hydroxyl ions to reach pH equilibrium leading to larger maghemite nanoparticles (50–60 nm). Spectroscopic analysis via Raman and FTIR analysis confirms the phases obtained. SEM and TEM imaging shows the correlation of structure orientation anisotropy which influenced the magnetic properties. Spherical magnetite nanoparticles strong dipolar interaction have higher coercivity (117G) and remanence (12 emu g−1) compared to the synthesised maghemite spinel needle-like structure nanoparticles. The understanding of the iron oxide structure directing effect by complex pH solution mechanism was essential for not only to prepare different forms of iron oxide and hydroxides but also controlled synthesis reproducibility.

Domain formation in rectangular magnetic nanoparticle assemblies

Rectangular assemblies with different aspect ratios were prepared with spherical magnetite nanoparticles (diameter $d=20\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$) on lithographically patterned substrates using a variant of the meniscus force deposition method. The aspect ratio (width:length) of the rectangular assemblies was varied from very low (1:1) to very high (1:1000) values. Angle-dependent ferromagnetic resonance measurements were performed to study the influence of the shape anisotropy on the magnetic properties. Using an analytical model based on the Smit-Suhl formalism for single-domain magnets, the demagnetizing factors were determined. The analysis of the resonance signals shows that, for small aspect ratios, the ratio of the in-plane demagnetization factors is inversely proportional to the corresponding ratio of width:length; that is, the assemblies behave like a single ferromagnet due to dipolar magnetic coupling between the particles. At larger aspect ratios a more complicated behavior is observed which indicates the formation of a multidomain-like structure inside the assemblies caused by geometrical inhomogeneities in the filling of the assemblies. Micromagnetic simulations of the magnetic properties of the assemblies support this assumption qualitatively and suggest that the formation of these inhomogeneities can be controlled by the fabrication process. The results provide insights into the collective magnetic behavior of nanoparticle assemblies, highlighting the high degree of tunability of the magnetic properties of such assemblies, which makes them promising building blocks for future magnetic devices.

Development of Co3[Co(CN)6]2/Fe3O4 Bifunctional Nanocomposite for Clinical Sensor Applications

In this study, a magnetically separable three-dimensional (3D) Co3[Co(CN)6]2/Fe3O4 nanocomposite comprising magnetic nanoparticles (NPs) adsorbed on the nanocubes of a cobalt Prussian blue analogue was prepared. The nanocomposite exhibited enhanced electrochemical performance in Co2+/Co3+ conversion, while the superparamagnetic behavior of the magnetite NPs was preserved even after adsorption on the nanocubes. Increased Faradaic currents were observed in the cyclic voltammograms (CV) for Co3[Co(CN)6]2/Fe3O4 in comparison with the CV of isolated Co3[Co(CN)6]2. This increase was attributed to supramolecular charge transfer between the cobalt Prussian blue analogue and the magnetic NPs and the larger amount of electroactive species on the electrode. Transmission electron microscopy images showed well-defined Co3[Co(CN)6]2 nanocubes that had edge lengths of 21–140 nm and were decorated with spherical magnetite NPs less than 10 nm in diameter. Interestingly, an intimate contact between the nanocubes and aggreg...

Specific Absorption Rate of Assembly of Magnetite Nanoparticles with Cubic Magnetic Anisotropy

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Magnetic Vortices as Efficient Nano Heaters in Magnetic Nanoparticle Hyperthermia

Magnetic vortices existing in soft magnetic nanoparticles with sizes larger than the single-domain diameter can be efficient nano-heaters in biomedical applications. Using micromagnetic numerical simulation we prove that in the optimal range of particle diameters the magnetization reversal of the vortices in spherical iron and magnetite nanoparticles is possible for moderate amplitudes of external alternating magnetic field, H0 < 100 Oe. In contrast to the case of superparamagnetic nanoparticles, for the vortex configuration the hysteresis loop area increases as a function of frequency. Therefore, high values of the specific absorption rate, on the order of 1000 W/g, can be obtained at frequencies f = 0.5–1.0 MHz. Because the diameter D of a non single-domain particle is several times larger than the diameter d of a superparamagnetic particle, the volume of heat generation for the vortex turns out to be (D/d)3 times larger. This shows the advantage of vortex configurations for heat generation in alternating magnetic field in biomedical applications.

Facile electrosynthesis and characterization of superparamagnetic nanoparticles coated with cysteine, glycine and glutamine

A novel and facile strategy has been developed for the preparation of cysteine-, glycine- and glutamine-coated magnetite nanoparticles (MNPs). According to this strategy, Fe3O4 nanoparticles were electrodeposited from an aqueous electrolyte containing a dissolved iron salt and amino acids. A simple deposition mode i.e., constant current and two-electrode set-up was used in the electrosynthesis procedure. The magnetite phase of the deposited nanoparticles was confirmed through XRD and FT-IR analyses. Morphological observations through FE-SEM and TEM confirmed the formation of spherical MNP particles with an average size of 10 nm. The formation of cysteine, glycine and glutamine layers on the surface of the electro-synthesized particles was proved based on FT-IR, DLS and TG data. Vibrating sample magnetometery (VSM) measurements confirmed the prepared iron oxide nanoparticles to have a super-paramagnetic nature, since they exhibit a high saturation magnetization (Ms ≈ 58 emu g−1), as well as, negligible remnant magnetization (Mr) and coercivity (Ce). Based on the obtained results, the proposed platform can be considered as a fast, simple and efficient method for the preparation of surface-coated magnetite nanoparticles.

Ethylenediaminetetraacetic acid capped superparamagnetic iron oxide (Fe3O4) nanoparticles: A novel preparation method and characterization

A novel and facile strategy is introduced for the preparation of ethylenediaminetetraacetic acid (EDTA) capped magnetite nanoparticles (MNPs). In this strategy, Fe3O4 nanoparticles were electrodeposited from a deposition bath containing 0.005M Fe2+/Fe3+ nitrate and chlorides alts and 1g/L EDTA. A simple deposition mode i.e. constant current and two-electrode set-up was used in the electro-synthesis procedure. The magnetite phase of the deposited nanoparticles was confirmed through XRD and FT-IR analyses. Morphological observations through FE-SEM and TEM confirmed the formation of spherical MNP particles with an average size of 10nm. The EDTA layer on the surface of the electro-synthesized magnetite nanoparticles was proved based on FT-IR, DLS and TG data. Vibrating sample magnetometer (VSM) measurements confirmed the EDTA capped iron oxide nanoparticles to have a super-paramagnetic nature, since they exhibit a high saturation magnetization (Ms=51.9emug−1), as well as, negligible remnant magnetization (Mr=0.59emug−1) and coercivity (Hc=0.85Oe). Based on the obtained results, the proposed platform can be considered as a fast, simple and efficient method for the preparation of the EDTA capped magnetite nanoparticles.

AC susceptibility as a tool to probe the dipolar interaction in magnetic nanoparticles

The dipolar interaction is known to substantially affect the properties of magnetic nanoparticles. This is particularly important when the particles are kept in a fluid suspension or packed within nano-carriers. In addition to its usual long-range nature, in these cases the dipolar interaction may also induce the formation of clusters of particles, thereby strongly modifying their magnetic anisotropies. In this paper we show how AC susceptibility may be used to obtain information regarding the influence of the dipolar interaction in a sample. We develop a model which includes both aspects of the dipolar interaction and may be fitted directly to the susceptibility data. The usual long-range nature of the interaction is implemented using a mean-field approximation, whereas the particle-particle aggregation is modeled using a distribution of anisotropy constants. The model is then applied to two samples studied at different concentrations. One consists of spherical magnetite nanoparticles dispersed in oil and the other of cubic magnetite nanoparticles embedded on polymeric nanospheres. We also introduce a simple technique to address the presence of the dipolar interaction in a given sample, based on the height of the AC susceptibility peaks for different driving frequencies.

Tunable High Aspect Ratio Iron Oxide Nanorods for Enhanced Hyperthermia

Despite magnetic hyperthermia being considered one of the most promising techniques for cancer treatment, until now spherical magnetite (Fe3O4) or maghemite (γ-Fe2O3) nanoparticles, which are the most commonly employed and only FDA approved materials, yield the limited heating capacity. Therefore, there is an increasing need for new strategies to improve the heating efficiency or the specific absorption rate (SAR) of these nanosystems. Recently, a large improvement in SAR has been reported for nanocubes of Fe3O4 relative to their spherical counterpart, as a result of their enhanced surface anisotropy and chainlike particle formation. Considering the proven advantages of high aspect ratio one-dimensional (1D) Fe3O4 nanostructures over their spherical and cubic counterparts, such as larger surface area, multisegmented capabilities, enhanced blood circulation time, and prolonged retention in tumors, we propose a novel approach that utilizes this 1D nanostructure for enhanced hyperthermia. Here, we demonstrat...

High-performance iron oxide nanoparticles for magnetic particle imaging - guided hyperthermia (hMPI).

Magnetic particle imaging (MPI) is an emerging imaging modality that allows the direct and quantitative mapping of iron oxide nanoparticles. In MPI, the development of tailored iron oxide nanoparticle tracers is paramount to achieving high sensitivity and good spatial resolution. To date, most MPI tracers being developed for potential clinical applications are based on spherical undoped magnetite nanoparticles. For the first time, we report on the systematic investigation of the effects of changes in chemical composition and shape anisotropy on the MPI performance of iron oxide nanoparticle tracers. We observed a 2-fold enhancement in MPI signal through selective doping of magnetite nanoparticles with zinc. Moreover, we demonstrated focused magnetic hyperthermia heating by adapting the field gradient used in MPI. By saturating the iron oxide nanoparticles outside of a field free region (FFR) with an external static field, we can selectively heat a target region in our test sample. By comparing zinc-doped magnetite cubic nanoparticles with undoped spherical nanoparticles, we could show a 5-fold improvement in the specific absorption rate (SAR) in magnetic hyperthermia while providing good MPI signal, thereby demonstrating the potential for high-performance focused hyperthermia therapy through an MPI-guided approach (hMPI).

Synthesis and optimization of methods for the production of magnetite nanoparticles with different sizes and morphology for biological application

Herein we report on the synthesis, optimization of the synthetic procedure, functionalization, and characterization of cubic and spherical superparamagnetic magnetite nanoparticles. Spherical nanoparticles (16 ± 2 nm) were synthesized using oleylamine and oleic acid, and cubic (20 ± 2, 5 ± 0.5 nm) nanoparticles were synthesized with oleic acid and small amounts of oleylamine. Covalent modification of the nanoparticles was carried out using heterobifunctional PEG with aminopropyltriethoxysilane and N-hydroxysuccinimide ester moieties. This modification makes both water emulsion stability and further modification of the nanoparticles with cytotoxic drugs possible.

Dialkylamide as Both Capping Agent and Surfactant in a Direct Solvothermal Synthesis of Magnetite and Titania Nanoparticles

An ecofriendly, low-cost, one-pot solvothermal approach has been developed to prepare spherical magnetite nanoparticles with sizes in the 7–12 nm range capped with a dialkylamine. Iron isopropoxide, water vapor, absolute ethanol, oleic acid, and oleylamine were used as iron oxide precursor, hydrolysis agent, solvent and surfactants, respectively. The surfactants’ role was investigated and an accurate correlation among the synthetic parameters, the crystallographic phases, and both crystallite and particle size was found. The amounts of oleylamine and oleic acid and the temperature have been revealed to be the key parameters in order to tune particle size and their polydispersity. An in-depth study on the role of each surfactant has pointed out the fundamental role of the amine as a reduction promoter as demonstrated by using different amines and confirmed by Mössbauer measurements. A dual 1H NMR-Fourier transform infrared spectroscopy approach on selected experiments for the investigation of the capping agents (in the presence of a magnetic phase (Magnetite) or a diamagnetic one (Anatase) prepared in the same synthetic conditions) has been found to be fundamental to clarify the actual nature of the capping agent of the nanoparticles and the reactions involved between the surfactants. New insights on the reaction mechanism confirm the formation of an amide that represents a new cosurfactant for the size and shape regulation and a biocompatible molecular coating of magnetite and anatase nanoparticles.

Quantitative phase analysis and microstructure characterization of magnetite nanocrystals obtained by microwave assisted non-hydrolytic sol–gel synthesis

An innovative preparation procedure, based on microwave assisted non-hydrolytic sol–gel synthesis, to obtain spherical magnetite nanoparticles was reported together with a detailed quantitative phase analysis and microstructure characterization of the synthetic products. The nanoparticle growth was analyzed as a function of the synthesis time and was described in terms of crystallization degree employing the Rietveld method on the magnetic nanostructured system for the determination of the amorphous content using hematite as internal standard. Product crystallinity increases as the microwave thermal treatment is increased and reaches very high percentages for synthesis times longer than 1h. Microstructural evolution of nanocrystals was followed by the integral breadth methods to obtain information on the crystallite size-strain distribution. The results of diffraction line profile analysis were compared with nanoparticle grain distribution estimated by dimensional analysis of the transmission electron microscopy (TEM) images. A variation both in the average grain size and in the distribution of the coherently diffraction domains is evidenced, allowing to suppose a relationship between the two quantities. The traditional integral breadth methods have proven to be valid for a rapid assessment of the diffraction line broadening effects in the above-mentioned nanostructured systems and the basic assumption for the correct use of these methods are discussed as well.

Preparation and Characterization of Magnetite Nanoparticles

The preparation of magnetite nanoparticles with controlled size has attracted of scientific and technological broad attention. Spherical magnetite nanoparticles in the size range from 8nm to 22 nm were synthesized by coprecipiation method using hexadecyl trimethyl ammonium bromide (CTAB) as dispersant. Magnetite nanoparticles have good dispersibility and uniform particles size distribution. The properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), automated surface area and pore size analyzer, vibrating sample magnetometer (VSM) and the catalytic performance was measured using high performance liquid chromatography (HPLC). The saturation magnetization is 13.785emu/g, and the coercive force of the sample is 23.738G, the average size of the particles is 13.6 nm, specific surface area is 19.318 m2/g and phenol conversion is up to 99.5%. These results indicate the synthesized magnetite particles have good performance.

Preparation and Complex Characterization of Magnetic Nanoparticles in Magnetic Fluid

This paper deals with the preparation and complex characterization of magnetite nanoparticles (MNPs), stabilized with sodium oleate (SO), by the routine methods such as infrared spectroscopy (FTIR), magnetic measurements, scanning electron microscopy (SEM) and dynamic light scattering (DLS). The FTIR spectra showed that SO molecules were linked to MNPs through chemical bonding. Magnetic measurements proved that the MNPs are superparamagnetic in nature. Four di erent methods were used to determine the size and size distribution of the MNPs: SEM, DLS, di erential centrifugal sedimentation (DCS) and magnetic measurements. SEM analysis showed a relatively narrow size distribution of roughly spherical MNPs with a mean diameter of 61 nm. DLS analysis con rmed monodispersed MNPs production with hydrodynamic diameter of 75 nm. The size distribution determined by DCS was found to be 69 nm. Finally, the calculated magnetic core diameter obtained from magnetization curve was 10 nm. The obtained results demonstrate that SO coated MNPs ful l the requirements for a useful drug delivery system.

Antibody - Conjugated Superparamagnetic Iron Oxide Nanoparticles for Active Targeting of Adenosine Receptors

Superparamagnetic iron oxide nanoparticles (SPIO) are regarded as advanced tools in biomedical science in disease diagnostics and therapies. We report the synthesis of antibody-conjugated nanoparticles (Ab-SPIO) that combine MRI behavior of nanoparticles with the selective and specific targeting of cellular proteins. Our novel Ab-SPIO will serve as a MRI biomarker for preventive PAH diseases. It is known that adenosine 1-type receptors (A1R) are involved in several cardiovascular diseases and offer promising therapeutic potential. In our study, we developed new A1R antibodies (Ab) conjugated SPIO nanocarriers as a specific Ab-MRI contrast agent. Spherical magnetite nanoparticles with a hydrodynamic diameter of 145 nm and particle size distribution of 15 - 60 nm were obtained. Surface of SPIO nanoparticles was stabilized by biocompatible polymer carboxymethyl cellulose (CMC) and precisely characterized in stability by measuring of zeta potential (- 43 mV). Strong magnetic response with a saturation magnetization of 75 Am2/kg confirmed appropriate magnetic behavior for MRI application. Oriented immobilization of antibody (Adenosine A1-R Antibody (H-40)) on free carboxyl groups of CMC provides active targeting of adenosine receptors. We conducted microscopic evaluation of the Ab-SPIO probe in VVEC cells, localization (plasma membrane vs. intracellular), and we determined the effects of hypoxia on A1R expression, compared A1R expression in VVEC-Hyp vs. VVEC-Co, and determined the effects of acute hypoxia on A1R expression in VVEC-Hyp vs. VVEC-Co. The experiments are proposed for MRI imaging of VV in control and hypoxic animals.Functionalized A1R-Ab-SPIO complexes will be utilized as a specific MRI biomarker in early disease diagnostics.

Magnetoresistance and electroresistance effects in Fe3O4 nanoparticle system

Nearly monodisperse spherical magnetite (Fe3O4) nanoparticles are prepared by colloidal chemistry route. Magnetic and electronic transport properties of the annealed pellets of these nanoparticles are reported. Effect of external magnetic and electric fields on the magnetic and transport properties of the material are studied as a function of temperature. We find that the highest resistance state of the ferromagnetic system occurs at a magnetic field which is approximately equal to its magnetic coercivity; this establishes the magnetoresistance (MR) in this system to be of the conventional tunnelling type MR as against the spin-valve type MR found more recently in some ferromagnetic oxide systems. The material also shows electroresistance (ER) property with its low-temperature resistance being strongly dependent on the excitation current that is used for the measurement. This ER effect is concluded to be intrinsic to the material and is attributed to the electric field-induced melting of the charge-order state in magnetite.

Transient magnetic birefringence for determining magnetic nanoparticle diameters in dense, highly light scattering media

The increasing use of biofunctionalized magnetic nanoparticles in biomedical applications calls for further development of characterization tools that allow for determining the interactions of the nanoparticles with the biological medium in situ. In cell-incubating conditions, for example, nanoparticles may aggregate and serum proteins adsorb on the particles, altering the nanoparticles’ performance and their interaction with cell membranes. In this work we show that the aggregation of spherical magnetite nanoparticles can be detected with high sensitivity in dense, highly light scattering media by making use of magnetically induced birefringence. Moreover, the hydrodynamic particle diameter distribution of anisometric nanoparticle aggregates can be determined directly in these media by monitoring the relaxation time of the magnetically induced birefringence. As a proof of concept, we performed measurements on nanoparticles included in an agarose gel, which scatters light in a similar way as a more complex biological medium but where particle–matrix interactions are weak. Magnetite nanoparticles were separated by agarose gel electrophoresis and the hydrodynamic diameter distribution was determined in situ. For the different particle functionalizations and agarose concentrations tested, we could show that gel electrophoresis did not yield a complete separation of monomers and small aggregates, and that the electrophoretic mobility of the aggregates decreased linearly with the hydrodynamic diameter. Furthermore, the rotational particle diffusion was not clearly affected by nanoparticle–gel interactions. The possibility to detect nanoparticle aggregates and their hydrodynamic diameters in complex scattering media like cell tissue makes transient magnetic birefringence an interesting technique for biological applications.

Synthesis, characterization and magnetic properties of polymer–Fe3O4 nanocomposite

The chemical stability of magnetic particles is of great importance for their applications in medicine and biotechnology. The most challenging problem in physics of disordered systems of magnetic nanoparticles is the investigation of their dynamic properties. The chemical coprecipitation process was used to synthesize spherical magnetite nanoparticles of 14nm. The as-prepared magnetite nanoparticles have been aged in the matrix. Magnetic properties and aging effect were studied by Mössbauer spectroscopy at temperatures ranging from 77 to 300K, and X-ray diffraction. At room temperature, the Mössbauer spectrum showed superparamagnetic behavior of the particles, while well-defined sextets were observed at 77K, indicating a blocked regime. The superparamagnetic magnetite nanoparticles can be used as microbead biosensors.