Superparamagnetic Magnetite Research Articles

Enhancement of GAD Storage Stability with Immobilization on PDA-Coated Superparamagnetic Magnetite Nanoparticles

To improve the storage stability of glutamic acid decarboxylase (GAD), superparamagnetic magnetite (Fe3O4) nanoparticles were synthesized by co-precipitation method and coated with polydopamine (PDA) for GAD immobilization. Dynamic light scattering and transmission electron microscopy were used to determine size of the nanoparticles, which were approximately 10 nm, increasing to 15 nm after PDA-coating and to 20 nm upon GAD binding. Vibrational scanning measurements significantly represented the superparamagnetic behavior of the Fe3O4, and X-ray diffraction analysis confirmed that the crystalline structure before and after coating with PDA and the further immobilization of GAD remained the same. Thermogravimetric analysis and Fourier-transform infrared spectroscopy proved that the PDA-coating on Fe3O4 and further immobilization of GAD were successful. After immobilization, the enzyme can be used with a relative specific activity of 40.7% after five successive uses. The immobilized enzyme retained relative specific activity of about 50.5% after 15 days of storage at 4 °C, while free enzyme showed no relative specific activity after two days of storage. The GAD immobilization on PDA-coated magnetite nanoparticles was reported for the improvement of enzyme storage stability for the first time.

Relationship between nanostructure-magnetic property induced by temperature for iron oxide nanoparticles in vacuum, Ar and O2 environments

It is known that superparamagnetic magnetite (Fe3O4) nanoparticles (NPs) become ferromagnetic under Si2+ ion irradiation due to particle size growth and microstructure evolution; it has been proposed that this feature could be used for in situ high temperature (up to 500 °C) radiation monitoring in the core of nuclear reactors. Herein, magnetite NPs synthesized by a nanocluster deposition system are heated to 800 °C in three different environments (argon, oxygen and vacuum), and nanostructure-magnetic property correlations are investigated by vibrating sample magnetometry, scanning electron microscopy, and X-ray diffraction. Magnetization of the NPs is increased due to the sintering and overall size growth by the agglomeration of the particles, while the morphology remains nearly unchanged up to 800 °C, with the one anomaly that zerovalent Fe appeared due to the reduction of the Fe3O4 at 800 °C in vacuum. In argon and oxygen at high-temperature, antiferromagnetic hematite is created, which causes a reduction of the magnetization, and abrupt growth of particle size above 500 °C.

A Simple and Reliable Synthesis of Superparamagnetic Magnetite Nanoparticles by Thermal Decomposition of Fe(acac)3

Magnetic nanoparticles have been largely proposed as means of technological tools due to its value in different fields, especially in biomedicine. Herein, we present a robust, highly reproducible and low-cost method to obtain superparamagnetic magnetite nanoparticles (MNP-II) of about 15±5 nm diameter by thermal decomposition of [Fe(acac)3] in a one-pot, two-step method. In the first step, magnetite nanoparticles (MNP-I) of lower size, 9±4 nm, with a saturation magnetization (MS) of 65 emu/g and a coercive field (Hc) of 1 Oe are obtained. In the second step, those particles MNP-I act as seeds for the final MNP-II which present a saturation magnetization of 70 emu/g and a coercive field of 12 Oe.

Ultra-low remanence and weak magnetic agglomeration of superparamagnetic magnetite nanoparticles caused by high magnetic moment Tb3+ doping

The structure and magnetic properties of the magnetite can be substantial corrected by incorporating foreign cations. In this work, Tb3+ was successfully incorporated into magnetite and superparamagnetic magnetite nanoparticles were obtained, using solvothermal method. The doping of Tb3+ greatly reduces the Mr and Hc values of the magnetite. Due to the doping of high magnetic moment Tb3+, the original magnetic moment of the magnetite is destroyed and magnetic domain are decomposed, resulting in a significant reduction in remanence and magnetic agglomeration. The remarkable effect of Tb3+ doping degaussing will provide new prospects for the application of magnetite materials in the superparamagnetic direction.

Potential anticancer activity of protocatechuic acid loaded in montmorillonite/Fe3O4 nanocomposites stabilized by seaweed Kappaphycus alvarezii.

Superparamagnetic magnetite nanocomposites (Fe3O4-NCs) were successfully synthesized, which comprised of montmorillonite (MMT) as matrix support, Kappaphycus alvarezii (SW) as bio-stabilizer and Fe3O4 as filler in the composites to form MMT/SW/Fe3O4-NCs. Nanocomposite with 0.5 g Fe3O4 (MMT/SW/0.5Fe3O4) was selected for anticancer activity study because it revealed high crystallinity, particle size of 7.2 ± 1.7 nm with majority of spherical shape, and Ms = 5.85 emu/g with negligible coercivity. Drug loading and release studies were carried out using protocatechuic acid (PCA) as the model for anticancer drug, which showed 19% and 87% of PCA release in pH 7.4 and 4.8, respectively. Monolayer anticancer assay showed that PCA-loaded MMT/SW/Fe3O4 (MMT/SW/Fe3O4-PCA) had selectivity towards HCT116 (colorectal cancer cell line). Although MMT/SW/Fe3O4-PCA (0.64 mg/mL) showed higher IC50 than PCA (0.148 mg/mL) and MMT/SW/Fe3O4 (0.306 mg/mL, MMT/SW/Fe3O4-PCA showed more effective killing towards tumour spheroid model generated from HCT116. The IC50 for MMT/SW/Fe3O4-PCA, MMT/SW/Fe3O4 and PCA were 0.132, 0.23 and 0.55 mg/mL, respectively. This suggests the improved penetration efficiency and drug release of MMT/SW/Fe3O4-PCA towards HCT116 spheroids. Moreover, concentration that lower than 2 mg/mL MMT/SW/Fe3O4-PCA did not result any hemolysis in human blood, which suggests them to be ideal for intravenous injection. This study highlights the potential of MMT/SW/Fe3O4-NCs as drug delivery agent.

Cr(VI) Adsorption on Engineered Iron Oxide Nanoparticles: Exploring Complexation Processes and Water Chemistry.

Surface-functionalized magnetic nanoparticles are promising adsorbents due to their large surface areas and ease of separation after contaminant removal. In this work, the affinity of Cr(VI) adsorption to 8 nm surface-functionalized superparamagnetic magnetite nanoparticles was determined for surface coatings with amine (trimethyloctadecylammonium bromide, CTAB) and carboxyl (stearic acid, SA) functional groups. Cr(VI) adsorbed more strongly to the CTAB-coated nanoparticles than to the SA-coated materials due to electrostatic interactions between positively charged CTAB and anionic Cr(VI) species. The adsorption of Cr(VI) by CTAB- and SA-coated nanoparticles increased with decreasing pH (4.5-10), which could be simulated by a surface complexation model. Cr(VI) removal performance by the nanocomposite was evaluated for two realistic drinking water compositions. The co-occurrence of divalent cations (Ca2+ and Mg2+) and Cr(VI) resulted in decreased Cr(VI) adsorption as particles were destabilized, leading to the aggregation and lower effective surface area, confirming the importance of the overall water composition on the performance of novel engineered nanomaterials for water treatment applications.

Wildfire severity: Environmental effects revealed by soil magnetic properties

AbstractStrong wildfires pose significant damage to all soil qualities and lead to land degradation. The complex nature and properties of fire‐derived materials require multidisciplinary efforts for their reliable characterization. The main objective of our study was to evaluate the suitability of magnetic properties of fire‐affected soils as proxy parameters for wildfire severity and to relate magnetic signature of burnt soils to carbon and nitrogen contents as influenced by wildfires. We present mineral magnetic investigation of 22 sites with wildfire‐affected soils and 17 nonburnt soils from nearby locations. We employed measurements of magnetic susceptibility and anhysteretic remanence in combination with scanning and transmission electron microscopy observations on magnetic particles from burnt soils and ashes. Bulk soil and vegetation ash analyses of total carbon and nitrogen, organic carbon, and elemental content were carried out as well. We show that pyrogenic magnetic enhancement is restricted to the uppermost 0‐ to 2‐cm soil depth and can be used as a proxy for wildfire severity. Strong wildfires lead to the production of nanometer‐sized superparamagnetic magnetite and/or maghemite particles and smaller amount of single‐domain fraction. These strongly magnetic minerals have typical characteristics of high‐temperature combustion products with spherical shape and diameters between 0.1 and 2 μm. Fire‐affected soils show relative enrichment with phosphorous, manganese, and heavy metals (Cu, Pb, Zn, Ni, Co, and As) calculated with respect to soils from nonburnt nearby localities. Our results demonstrate the potential of environmental magnetic methods as an additional tool for assessment of wildfire severity and the content of main soil nutrients.

Ferritin RNA interference inhibits the formation of iron granules in the trophocytes of worker honey bees (Apis mellifera)

Iron granules containing superparamagnetic magnetite act as magnetoreceptor for magnetoreception in honey bees. Biomineralization of iron granules occurs in the iron deposition vesicles of trophocytes and requires the participation of actin, myosin, ferritin2, and ATP synthase. The mechanism of magnetoreception in honey bees can be explored by suppressing the formation of iron granules. Toward this goal, we injected double-stranded RNA of ferritin2 and ferritin1 into newly emerged worker honey bees to knock down these genes via RNA interference. We confirmed that mRNA and protein production of the ferritins was inhibited, leading to immature iron granules. Downregulating ferritin2 and ferritin1, moreover, leads to different deposition morphology of 7.5-nm diameter iron particles, indicating that the two genes play different roles in the formation of iron granules in worker honey bees.

Symbiosis of Silica Biomorphs and Magnetite Mesocrystals

AbstractSilica biomorphs are extraordinary inorganic superstructures formed via autocatalytic co‐precipitation and bottom‐up self‐assembly of alkaline‐earth carbonates and silica. However, they show no inherent functionality except for their striking textural motifs and curved morphologies. This work presents strategies to magnetize silica biomorphs, thus creating thermally stable ceramic microswimmers with unique elaborate shapes. This is achieved by growing super paramagnetic magnetite mesocrystals on and around the complex curved surfaces of biomorphs, while keeping their morphology and maintaining mesocrystal integrity. Selective mesocrystal formation on certain parts of the substrates is induced by chemical modification of the biomorph surface, increasing the loading of magnetite on the silica–carbonate structures and, in suitable cases, rendering them able to respond to external magnetic fields and move as microswimmer entities. In this way, the complex ultrastructure of silica biomorphs is successfully used as a template for functional ceramics. Furthermore, selective dissolution of the carbonate core from the biomorphs leads to hollow magnetic structures that could be filled with actives, thus serving as microcarriers with considerable loading capacity.

Liquid reconfigurable ferromagnetic materials

Magnetic Materials Ferromagnetic materials show a permanent magnetic dipole, whereas superparamagnetic ones only show magnetic properties under an applied field. Some materials, like ferrofluids, show liquid-like behavior but do not retain their magnetization in the absence of an applied field. Liu et al. show remnant magnetization of otherwise superparamagnetic magnetite nanoparticles at an oil-water interface of emulsion droplets (see the Perspective by Dreyfus). The permanent magnetization could be controlled by coupling and uncoupling the magnetization of individual nanoparticles, making it possible to “write and erase” shapes of the droplets or to elongate them into cylinders. Science , this issue p. [264][1]; see also p. [219][2] [1]: /lookup/doi/10.1126/science.aaw8719 [2]: /lookup/doi/10.1126/science.aax8979

Reconfigurable ferromagnetic liquid droplets.

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.

Rock magnetic constraints for the Mid-Miocene Climatic Optimum from a high-resolution sedimentary sequence of the northwestern Qaidam Basin, NE Tibetan Plateau

The thick sequence of Cenozoic deposits in the Qaidam Basin of the NE Tibetan Plateau has great potential for understanding the tectonic and climatic evolution of the region. In this study, we performed detailed rock magnetic analyses of a well-dated (~20.7–11.2 Ma) Upper Cenozoic sedimentary sequence from the Huatugou (HTG) section in the NW Qaidam Basin. The magnetic susceptibility of the sequence is relatively low before 17.4 Ma, high during 17.4–14.5 Ma, and lower after 14.5 Ma again. This pattern is consistent with the occurrence of the Mid-Miocene Climatic Optimum (MMCO) during 17.4–14.5 Ma, with global climatic cooling thereafter. Measurements of multiple rock magnetic parameters indicate a peak in the concentration of fine-grained magnetic minerals during 17.4–14.5 Ma. This feature demonstrates that the enhancement of the magnetic susceptibility is due to the pedogenic production of superparamagnetic (SP) and single domain (SD) magnetite, suggesting the occurrence of relatively high effective precipitation and high temperature in the Qaidam Basin at this time. Comparing with regional and global climatic records, the warm and humid climatic conditions coincide with the MMCO, implying that global climate changes were responsible for the climatic evolution in the Qaidam Basin throughout the MMCO. However, after 14.5 Ma, the rapid uplift of the northern Tibetan Plateau caused it to reach a critical elevation which blocked the moisture supply to the Qaidam Basin and may also have contributed to the observed climatic changes.

The role of spin-phonon coupling in enhanced desorption kinetics of antioxidant flavonols from magnetic nanoparticles aggregates

Abstract An important criterion in the evaluation of drug delivery systems based on nanoparticles is the drug release kinetics. From numerous published works, it is obvious that the fraction of the released drug as a function of time shows qualitatively the same behaviour, even when the release is assisted by an external force. In this study a series of experiments has been performed on a system that can be considered as the simplest drug delivery system. It consists only of uncoated/unprotected superparamagnetic magnetite nanoparticles in the form of mesoporous aggregates and adsorbed flavonols (quercetin, myricetin, or myricitrin). The simultaneous utilization of external permanent and oscillating magnetic fields remarkably accelerated the flavonol release. There is no a specific pulling force that eventually causes the rupture of the bonds between the molecules and the particle surface, i.e. the detachment of an individual molecule is thermally activated. The adsorption of molecules onto nanoparticles follows almost without delay quick changes in the field-induced motion of the nanoparticles, and they are subject to more frequent collisions with the surrounding solvent molecules. The barrier fluctuations occur due to the magnetic field dependence of the nanoparticle phonon spectra, to which the adsorbed flavonol molecule vibrations are strongly coupled. The phonon frequencies and phonon damping of a ferromagnetic nanoparticle are actually affected by the magnetic field through the spin-phonon coupling. The rate of release (spontaneous or forced) is invariably a first-order process, which can be considered a basic property of a broad class of drug nanodelivery systems.

Synthesis and physical investigation of PVA-based cast films reinforced with non-covalently functionalized magnetite-deposited carbon nanotubes

This paper describes the mechanical behavior of flexible polymer nanocomposite films loaded with MWCNT/Fe3O4 nanopowders as filler. A simple and expedite casting evaporation methodology was used for manufacturing the PVA-based films with a portion of HPC and PVDF polymers. The average crystallite size of superparamagnetic magnetite nanoparticles (NPs) deposited onto the functionalized carbon nanotubes (f-MWCNTs) was located between ca. 9.6–11.9 nm, while the analysis of VSM data came up with results showing an awful lot of magnetic strength for these treated nanopowders. A non-covalent functionalization procedure on the resultant colloidal MWCNT/Fe3O4 nanopowders was carried out by introducing hydrophilic PVA chains around the tubes. Importantly, the hypothesis behind our work was that the tight PVDF polymer could effectively enhance the tensile strength of soft PVA polymer film, whereas high-stretchable HPC polymer could be used to increase the elongation at break of PVA-based films. Advantageously, this idea therefore gave rise to interesting mechanical indices of PVA-based polymer films, and even as a significant observation it was found that the magnetic interactions between magnetite NPs could further amplify the mechanical stability of the specimens. We emphasize that the resultant MWCNT/Fe3O4-contained multi-polymer films are thus capable of being exploited in industrial and medical gadgets such as mechanical sensors, biohybrid swimmers, artificial hearts, mechanical respiration devices, and the like.

A comprehensive toxicity evaluation of novel amino acid-modified magnetic ferrofluids for magnetic resonance imaging.

Stem cells have been widely exploited as remedial agents in regenerative medicine due to its tremendous potential in treatment of various debilitating diseases. In spite of this fact, there is need of a reliable, clinically applicable cell tracker for deciphering the homing and distribution of stem cells post-transplantation. Researchers have proposed the use of superparamagnetic magnetite (Fe3O4) nanoparticles for in vivo and in vitro tracking and imaging of stem cells. However, there is not much understanding of the chemical coatings on the nanoparticles, which is very important for the sustainability of stem cells in biological system. For any biomedical applications, the surface properties and the core structure of nanoparticles play a significant role. This study reports surface modification of magnetic Fe3O4 nanofluid with biocompatible amino acids viz., arginine and histidine to maintain colloidal stability at neutral pH, impart least disruption when encountered with the biological system and allow labeling with mesenchymal stem cells (MSCs). The size of amino acids-modified magnetic nanoferrofluid (AA@MNFs) was restricted to 15-25nm for enhanced uptake in stem cells. In vitro cytotoxicity profile of stem cells labeled AA@MNFs was estimated using various assays like MTT, LDH and AO/EtBr followed by detailed pre-clinical toxicity assessment of AA@MNFs which illustrated least toxicity effects in major tissues of the animals. In vitro MRI scans of the stem cells labeled AA@MNFs confirmed the suitability of the reported ferrofluids for the use as MR contrast agents.

From gel-like Pickering emulsions to highly ordered superparamagnetic magnetite aggregates with embedded gold nanoparticles

Pickering emulsions with two types of nanoparticles, i.e., superparamagnetic magnetite nanoparticles dispersed in n-hexane and gold nanoparticles dispersed in water, were formed by rigorous mixing in presence of surface active polymeric surfactants. Monodisperse magnetite nanoparticles with a mean particle size of 4 nm were obtained by a microwave-assisted synthesis in n-hexane in presence of oleic acid, and gold nanoparticles were produced in aqueous solution in presence of the hyperbranched poly(ethyleneimine) (PEI) or sodium citrate as reducing and stabilizing agent. After mixing the prepared nanoparticle dispersions in presence of the Pluronics an intermediate gel-like phase is formed. The Pickering emulsion droplets in the intermediate phase are stabilized by both types of nanoparticles, as to be seen by cryo-SEM micrographs. After separating, solvent evaporation and redispersion in water highly ordered Pluronic-stabilized superparamagnetic magnetite nanoparticle aggregates with embedded gold nanoparticles can be obtained.

Size-controlled synthesis of superparamagnetic magnetite nanoclusters for heat generation in an alternating magnetic field

We report the size-controlled synthesis of monodisperse magnetite (Fe3O4) nanoclusters by a facile and economic solvothermal route by using polyacrylic acid (PAA) as the coordinative ligand. In comparison with previous reports, nanocluster sizes were tuned over a broad range of 640–250 nm while retaining the superparamagnetic behaviour in the present study. The nanocluster sizes are varied by changing the amounts of PAA as well as water added in the reaction medium during the solvothermal treatment. As-synthesized Fe3O4 nanoclusters are characterized using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The radio frequency alternating magnetic field induced heating studies indicate that the as-synthesized Fe3O4 nanoclusters are promising candidates for magnetic fluid hyperthermia applications. In the case of magnetic nanoclusters, consisting of individual superparamagnetic nanocrystals, the field induced heating occurs at two different length scale, viz. Neel-Brown relaxation of the individual superparamagnetic nanocrystals (length scale <10 nm) and Brownian relaxation of the entire nanoclusters (length scale ~250 nm or higher). Experimental findings indicate that the heating efficiency of the magnetic nanoclusters vary significantly with variations in the relaxation time at both length scales. The heating efficiency of the magnetic nanoclusters is also found to increase linearly with the square of the external field amplitudes, in accordance with the linear response theory.

Super-paramagnetic magnetite nanoparticles obtained by different synthesis and separation methods stabilized by biocompatible coatings

Magnetite nanoparticles were chemically synthesized by co-precipitation method, using gelatine added in-situ and ex-situ and also using two different separation techniques for the magnetite particles (magnet or centrifuge). The product was analysed by different techniques, such as SEM, DLS, FTIR and XRD. From the comparison of the results it was concluded that the added gelatine can be preserved in the final product with a higher probability if it is added ex-situ. This is because a larger and more uncertain part of gelatine is lost during the washing – separation steps when it is added in-situ. Thus, the ex-situ addition of gelatine is more efficient to stabilize nano-magnetite particles. Also, it was concluded that particle separation by centrifuge was more efficient to separate larger and mostly paramagnetic magnetite particles, while separation by a magnet was more efficient for smaller superparamagnetic magnetite particles. This is explained by different mechanism behind these two separation techniques. Thus, for the production of suspensions with superparamagnetic nano-magnetite particles the separation method using a strong magnet is preferred vs a centrifuge. It was further shown that when sucrose was applied together with gelatine, the stabilization of magnetite particles was improved compared to the case when only gelatine was used.

Preparation and characterization of superparamagnetic magnetite (Fe3O4) nanoparticles: A short review

Magnetic magnetite (Fe3O4) nanoparticles have attracted a great deal of attention in both fundamental research and practical applications over the past decades. Down to the nanoscale, superparamagnetic Fe3O4 nanoparticles with only a single magnetic domain exhibit high magnetic susceptibility, which provides a stronger and faster magnetic response. Their superparamagnetic properties together with other intrinsic properties such as low toxicity, high surface area-to-volume ratio and simple separation methodology, making them ideal for environmental remediation, biomedical, and agricultural applications. This review discusses three conventional wet chemical methods, including chemical co-precipitation, sol-gel synthesis and thermal decomposition for the preparation of superparamagnetic Fe3O4 nanoparticles with controlled size and magnetic properties. Nowadays, with the growing research interest in Fe3O4 nanoparticles, there is a great amount of researches reported on efficient routes to prepare size-controlled magnetic nanoparticles. Thus, this review is designed to report the recent information from synthesis to the characterization of Fe3O4 nanoparticles as well as the discussion of future perspective in this research area.

Adsorption of bovine serum albumin at oil-water interface in the presence of polyelectrolytes and nature of interaction forces

Here we report the adsorption behavior of protein at an oil-water interface, that is covered with polyelectrolytes (PE) and the interaction forces involved. The weak and strong PE’s used are poly(acrylic acid), PAA and poly(diallyldimethylammonium chloride), PDDA, respectively. The protein and oil used are bovine serum albumin (BSA) and octane droplets in water, containing superparamagnetic magnetite nanoparticles, respectively. The intermolecular forces, hydrodynamic diameter and electrophoretic mobility measurements are used to study the adsorption behavior of protein. The results showed an enhanced displacement of the adsorbed PDDA and PAA with increasing concentrations of BSA. In the absence of BSA, the emulsion droplets covered with PDDA and PAA exhibited a long range repulsive interaction. The addition of BSA into PDDA and PAA stabilized emulsion resulted in a decrease in the onset of interaction of repulsive force profile. The reversal of the sign and the change in the magnitude of zeta potential indicates the displacement of PDDA by BSA molecules at the oil-water (O/W) interface, which was in agreement with the findings of Satulovsky et.al. [Proc. Natl. Acad. Sci. 97 (2000) 9037–9041] that polymers on hydrophobic surfaces are not effective in preventing protein adsorption. These results indicate the displacement of macromolecule of very large molecular weight and preferential adsorption of small macromolecules at the O/W interfaces, irrespective of the nature of adsorbed PE’s (strong or weak, anionic or cationic with high or low charge density). These finding provides new insights into adsorption of proteins at the oil-water interfaces and may have important implication in tailoring industrial formulations with an extended shelf life and in increasing biocompatibility of implants.