Superparamagnetic Nanocrystals Research Articles

New sol-gel-derived magnetic bioactive glass-ceramics containing superparamagnetic hematite nanocrystals for hyperthermia application

Although the three main phases of iron oxide – hematite, maghemite, and magnetite – exhibit superparamagnetic properties at the nanoscale, only maghemite and magnetite phases have been explored in magnetic bioactive glass-ceramics aimed at applications in cancer treatment by hyperthermia. In this work, it is reported for the first time the superparamagnetic properties of hematite nanocrystals grown in a 58S bioactive glass matrix derived from sol-gel synthesis. The glass-ceramics are based on the (100-x)(58SiO2-33CaO-9P2O5)-xFe2O3 system (x = 10, 20 and 30 wt%). A thermal treatment leads to the growth of hematite (α-Fe2O3) nanocrystals, conferring superparamagnetic properties to the glass-ceramics, which is enough to produce heat under an external alternating magnetic field. Besides, the crystallization does not inhibit materials bioactivity, evidenced by the formation of calcium phosphate onto the glass-ceramic surface upon soaking in simulated body fluid. Moreover, their cytotoxicity is similar to other magnetic bioactive glass-ceramics reported in the literature. Finally, these results suggest that hematite nanocrystals' superparamagnetic properties may be explored in multifunctional glass-ceramics applied in bone cancer treatment by hyperthermia allied to bone regeneration.

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.

Evaluation of polyol‐made Gd3+‐substituted Co0.6Zn0.4Fe2O4 nanoparticles as high magnetization MRI negative contrast agents

AbstractThe structural, microstructural, and magnetic properties of ~5‐nm‐sized Co0.6Zn0.4Fe2 − xGdxO4 nanoparticles were investigated in order to evaluate their capability to enhance the magnetic resonance imaging contrast as high magnetization agents. A focus was made on the solubility of Gd3+ cations within the spinel lattice. By coupling X‐ray diffraction to X‐ray fluorescence spectroscopy, we demonstrated that only a limited fraction of Gd3+ can substitute Fe3+ ions into the whole crystal structure and does not exceed 6 at.‐%. At this concentration, the room temperature (27°C) saturation magnetizations of the prepared superparamagnetic nanocrystals were found to be close to 80 emu g−1. Coating these nanoparticles with hydrophilic dopamine ligands leads to the formation of ~50‐nm‐sized clusters in water. As a consequence, relatively high r2/r1 ratios of transverse to longitudinal proton relaxivities and high r2 values were measured in the resulting colloids at physiological temperature (37°C) for an applied magnetic field of 1.41 T: 33 and 188 mM−1 sec−1, respectively, for the richest system in gadolinium. Moreover, after incubation with healthy human model cells (fibroblasts) at doses as high as 10 μg mL−1, they induce neither cellular death nor acute cellular damage making the engineered probes particularly valuable for negative magnetic resonance imaging contrasting.

One-Pot Method for Preparation of Magnetic Multi-Core Nanocarriers for Drug Delivery.

The development of various magnetically-responsive nanostructures is of great importance in biomedicine. The controlled assembly of many small superparamagnetic nanocrystals into large multi-core clusters is needed for effective magnetic drug delivery. Here, we present a novel one-pot method for the preparation of multi-core clusters for drug delivery (i.e., magnetic nanocarriers). The method is based on hot homogenization of a hydrophobic phase containing a nonpolar surfactant into an aqueous phase, using ultrasonication. The solvent-free hydrophobic phase that contained tetradecan-1-ol, γ-Fe2O3 nanocrystals, orlistat, and surfactant was dispersed into a warm aqueous surfactant solution, with the formation of small droplets. Then, a pre-cooled aqueous phase was added for rapid cooling and the formation of solid magnetic nanocarriers. Two different nonpolar surfactants, polyethylene glycol dodecyl ether (B4) and our own N1,N1-dimethyl-N2-(tricosan-12-yl)ethane-1,2-diamine (SP11), were investigated for the preparation of MC-B4 and MC-SP11 magnetic nanocarriers, respectively. The nanocarriers formed were of spherical shape, with mean hydrodynamic sizes <160 nm, good colloidal stability, and high drug loading (7.65 wt.%). The MC-B4 nanocarriers showed prolonged drug release, while no drug release was seen for the MC-SP11 nanocarriers over the same time frame. Thus, the selection of a nonpolar surfactant for preparation of magnetic nanocarriers is crucial to enable drug release from nanocarrier.

Non-Aqueous Sol-Gel Synthesis of FePt Nanoparticles in the Absence of In Situ Stabilizers.

The synthesis of FePt nanocrystals is typically performed in an organic solvent at rather high temperatures, demanding the addition of the in situ stabilizers oleic acid and oleylamine to produce monomodal particles with well-defined morphologies. Replacing frequently-used solvents with organic media bearing functional moieties, the use of the stabilizers can be completely circumvented. In addition, various morphologies and sizes of the nanocrystals can be achieved by the choice of organic solvent. The kinetics of particle growth and the change in the magnetic behavior of the superparamagnetic FePt nanocrystals during the synthesis with a set of different solvents, as well as the resulting morphologies and stoichiometries of the nanoparticles were determined by powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES)/mass spectrometry (ICP-MS), and superconducting quantum interference device (SQUID) measurements. Furthermore, annealing of the as-prepared FePt nanoparticles led to the ordered L10 phase and, thus, to hard magnetic materials with varying saturation magnetizations and magnetic coercivities.

Surface-optimized core–shell nanocomposites (Fe3O4@MnxFeyO4) for ultra-high uranium sorption and low-field separation in water

In this work, we systematically design and synthesize manganese ferrite coated superparamagnetic magnetite nanocrystals, with oleylphosphate bilayer surface coatings (Fe3O4@MnxFeyO4@OP), for ultra high capacity uranium sorption and low-field magnetic-based separation in water.

Temperature dependence of the spin relaxation time of Fe3O4 and hemozoin superparamagnetic nanocrystals

We report experimental temperature and concentration dependences of the natural spin relaxation time of superparamagnetic Fe3O4 and hemozoin nanocrystals. We recorded the 1H NMR spectrum of 0.5% benzene dissolved in CS2 in function of superparamagnetic particle concentration and temperature, interpreting the 7.261±0.002ppm benzene line broadening. Our model for the line broadening includes natural, hyperfine magnetic dipole-dipole, and contact hyperfine contributions. The latter arises due to exchange interaction between benzene molecules and suspended nanoparticles. Estimated frequency of fluctuation in the 1 cm3 sample volume is in the 107Hz scale. Estimated natural electron spin-lattice relaxation frequencies of the superparamagnetic nanocrystals using frequency of fluctuations, and developed theoretical model applied to analysis of experimental data are in good agreement between each other. Thus the presently developed approach may be used to study fluctuations and natural spin-lattice relaxation frequencies in different media.

Luminescent/magnetic PLGA-based hybrid nanocomposites: a smart nanocarrier system for targeted codelivery and dual-modality imaging in cancer theranostics.

Cancer diagnosis and treatment represent an urgent medical need given the rising cancer incidence over the past few decades. Cancer theranostics, namely, the combination of diagnostics and therapeutics within a single agent, are being developed using various anticancer drug-, siRNA-, or inorganic materials-loaded nanocarriers. Herein, we demonstrate a strategy of encapsulating quantum dots, superparamagnetic Fe3O4 nanocrystals, and doxorubicin (DOX) into biodegradable poly(d,l-lactic-co-glycolic acid) (PLGA) polymeric nanocomposites using the double emulsion solvent evaporation method, followed by coupling to the amine group of polyethyleneimine premodified with polyethylene glycol-folic acid (PEI-PEG-FA [PPF]) segments and adsorption of vascular endothelial growth factor (VEGF)-targeted small hairpin RNA (shRNA). VEGF is important for tumor growth, progression, and metastasis. These drug-loaded luminescent/magnetic PLGA-based hybrid nanocomposites (LDM-PLGA/PPF/VEGF shRNA) were fabricated for tumor-specific targeting, drug/gene delivery, and cancer imaging. The data showed that LDM-PLGA/PPF/VEGF shRNA nanocomposites can codeliver DOX and VEGF shRNA into tumor cells and effectively suppress VEGF expression, exhibiting remarkable synergistic antitumor effects both in vitro and in vivo. The cell viability waŝ14% when treated with LDM-PLGA/PPF/VEGF shRNA nanocomposites ([DOX] =25 μg/mL), and in vivo tumor growth data showed that the tumor volume decreased by 81% compared with the saline group at 21 days postinjection. Magnetic resonance and fluorescence imaging data revealed that the luminescent/magnetic hybrid nanocomposites may also be used as an efficient nanoprobe for enhanced T2-weighted magnetic resonance and fluorescence imaging in vitro and in vivo. The present work validates the great potential of the developed multifunctional LDM-PLGA/PPF/VEGF shRNA nanocomposites as effective theranostic agents through the codelivery of drugs/genes and dual-modality imaging in cancer treatment.

Superparamagnetic Fe3O4/MWCNTs heterostructures for high frequency microwave absorption

Superparamagnetic Fe3O4 nanocrystals anchored on multiwalled carbon nanotubes (MWCNTs) were fabricated using co-precipitating technique which nicely integrates the magnetic and dielectric components into a synergistic microwave absorber.

Biomimetic Crystallization of MnFe2O4 Mediated by Peptide-Catalyzed Esterification at Low Temperature.

Enzymes are some of the most efficient catalysts in nature. If small catalytic peptides mimic enzymes, there is potential for broad applications from catalysis for new material synthesis to drug development, due to the ease of molecular design. Recently a hydrogel-based combinatory phage display library was developed and protease-mimicking peptides were identified. Here we advanced the previous discovery to apply one of these catalytic peptides for the synthesis of bimetal oxide nanocrystals through the catalytic ester-elimination pathway. Conventional bimetal oxide crystallization usually requires high temperatures above several hundred °C; however, this catalytic peptide could grow superparamagnetic MnFe2O4 nanocrystals at 4°C. Superconducting quantum interference device (SQUID) analysis revealed that MnFe2O4 nano-crystals grown by the catalytic peptide exhibit superpara-magnetism. This study demonstrates the usefulness of protease-mimicking catalytic peptides in the field of material synthesis.

Lactoferrin-assisted synthesis of zinc ferrite nanocrystal: Its magnetic performance and photocatalytic activity

Lactoferrin (LF) was used to assist the synthesis of zinc ferrite (ZnFe2O4, ZFO) semiconductor photocatalysts in this study, and superparamagnetic ZFO nanocrystals with an average crystallite size ranging from 11.3 nm to 20.1 nm were successfully obtained via the hydrothermal method. It was found that LF was conducive to fast formation of ZFO nuclei, which resulted in remarkable crystallinity enhancement of the as-prepared ZFO nanocrystals. The saturation magnetization (Ms) of the as-prepared ZFO crystals would be greatly improved with increasing the LF content, and the Ms of the as-prepared ZFO crystals synthesized with 50 mg of LF (ZFO-50LF) could reach 19.9 emu/g, whereas the Ms of the as-prepared ZFO crystals synthesized in the absence of LF (ZFO-0LF) was only 8.8 emu/g. In addition, although the specific surface area of ZFO-0LF nanocrystals (127.2 m2/g) was larger than that of ZFO-50LF nanocrystals (101.6 m2/g), and ZFO-0LF exhibited a higher absorption of methyl orange (MO) molecules in contrast with ZFO-50LF, but ZFO-50LF possessed a larger optical absorption coefficient, smaller band gap and higher photocatalytic degradation efficiency per unit area. After being irradiated under UV light for 3 h, ZFO-50LF almost could make MO molecules completely degrade. Therefore, the LF-assisted synthesized ZFO nanocrystals have a promising application prospect to be used as a new high-efficiency recyclable photocatalyst.

Superparamagnetic Liposomes for MRI Monitoring and External Magnetic Field‐Induced Selective Targeting of Malignant Brain Tumors

Magnetic‐fluid‐loadedliposomes (MFLs) of optimized magnetic responsiveness are newly worked out from the entrapment of superparamagnetic maghemite nanocrystals in submicronic PEG‐ylated rhodamine‐labelled phospholipid vesicles. This nanoplatform provides an efficient tool for the selective magnetic targeting of malignant tumors localized in brain and non‐invasive traceability by MRI through intravascular administration. As assessed by in vivo 7‐T MRI and ex vivo electron spin resonance, 4‐h exposure to 190‐T m–1 magnetic field gradient efficiently concentrates MFLs into human U87 glioblastoma implanted in the striatum of mice. The magnetoliposomes are then longer retained therein as checked by MRI monitoring over a 24‐h period. Histological analysis by confocal fluorescence microscopy confirms the significantly boosted accumulation of MFLs in the malignant tissue up to the intracellular level. Electron transmission microscopy reveals effective internalization by endothelial and glioblastoma cells of the magnetically conveyed MFLs as preserved vesicle structures. The magnetic field gradient emphasizes MFL distribution solely in the tumors according to the enhanced permeability and retention (EPR) effect while comparatively very low amounts are recovered in the other cerebral areas. Such a selective targeting precisely traceable by MRI is promising for therapeutic applications since the healthy brain tissue can be expected to be spared during treatments by deleterious anticancer drugs carried by magnetically guided MFLs.

X-Ray and Infrared Studies on Superparamagnetic Ni–Zn Ferrite Nanocrystals

Series of zinc-substituted nickel ferrite, Ni1−x ZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), nanoparticles were synthesized at low temperature by using sol–gel auto-combustion method. Powder X-ray diffraction confirmed the single-spinel structure of the synthesized Ni–Zn ferrite nanocrystals with average crystallite size was found to be 30 nm which is close to that of critical size for exhibiting superparamagnetism which was further verified from Mossbauer spectroscopic studies. The stoichiometric analysis of the ferrite samples carried out by employing energy-dispersive X-ray spectroscopy is found to be as expected. Results of infrared spectroscopic studies carried out on these superparamagnetic ferrite nanocrystals are reported in this paper. The tetrahedral and octahedral absorption band frequencies suggested the spinel structure of the ferrite samples and its behavior with zinc content x is attributed to the nanosize effect and occupation of zinc cations at the octahedral [B] sites. Further, the force constants are found to be in the reported range of that for ferrites.

Hydrophobic graphene nanosheets decorated by monodispersed superparamagnetic Fe3O4 nanocrystals as synergistic electromagnetic wave absorbers

Superparamagnetic Fe3O4 nanocrystals anchored on hydrophobic graphene nanosheets are prepared and are shown to act as synergistic electromagnetic wave absorbers with good stability.

Size- and composition-dependent radio frequency magnetic permeability of iron oxide nanocrystals.

We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals. All nanocrystalline samples are confirmed to be in the superparamagnetic state at room temperature by SQUID magnetometry. Through the one-turn inductor method, the ac magnetic properties of the nanocrystalline oxides are characterized. In magnetite-rich iron oxide nanocrystals, size-dependent magnetic permeability is not observed, while maghemite iron oxide nanocrystals show clear size dependence. The inductance, resistance, and quality factor of hand-wound inductors with a superparamagnetic composite core are measured. The superparamagnetic nanocrystals are successfully embedded into hand-wound inductors to function as inductor cores.

Magnetochromatic thin-film microplates.

A new type of magnetochromatic material is developed based on thin-film interference of microplates self-assembled from super-paramagnetic nanocrystals. Dynamic optical tuning can be achieved through orientational manipulation of free-standing super-paramagnetic thin-film microplates using external magnetic fields.

Magnetic, X-ray and Mössbauer studies on magnetite/maghemite core–shell nanostructures fabricated through an aqueous route

Uniform 6–13 nm sized 0D superparamagnetic Fe3O4 nanocrystals were synthesized by an aqueous ‘co-precipitation method’ under a N2 atmosphere as a function of temperature to understand the growth kinetics. The crystal phases, surface charge, size, morphology and magnetic characteristics of as-synthesized nanocrystals were characterized by XRD, Raman spectroscopy, FTIR, TG-DTA, BET surface area, dynamic light scattering along with zeta potential, HR-TEM, EDAX, vibrating sample magnetometry and Mossbauer spectroscopy. TEM investigation revealed highly crystalline spherical magnetite particles in the 8.2–12.5 nm size range. The kinetically controlled as-grown nanoparticles were found to possess a preferential (311) orientation of the cubic phase, with a highest magnetic susceptibility of ∼57 emu g−1. The Williamson–Hall technique was employed to evaluate the mean crystallite size and microstrain involved in the as-synthesized nanocrystals from the X-ray peak broadening. In addition to FTIR and Raman spectra, Rietveld structural refinement of XRD confirms the magnetite phase with 5–20% maghemite in the sample. VSM and Mossbauer spectral data allowed us to fit the magnetite/maghemite content to a core–shell model where the shell is 0.2–0.3 nm thick maghemite over a magnetite core. The activation energy of <10 kJ mol−1 calculated from an Arrhenius plot for the complex process of nucleation and growth by diffusion during synthesis shows the significance of the precipitation temperature in the size controlled fabrication processes of nanocrystals. Brunauer–Emmett–Teller (BET) results reveal a mesoporous structure and a large surface area of 124 m2 g−1. Magnetic measurement shows that the particles are ferromagnetic at room temperature with zero remanence and zero coercivity. This method produced highly crystalline and dispersed 0D magnetite nanocrystals suitable for biological applications in imaging and drug delivery.

Lethal drug combination: Arsenic loaded multiple drug mesoporous silica for theranostic applications

Simultaneous delivery of multiple therapeutic agents is of great importance for effective chemotherapy due of its well-known drug synergism and suppression to chemoresistance. We report a new theranostic nanoformulation to shuttle multiple chemotherapeutic agents for successfully exterminating cancer cells. This strategy is based on the fabrication of magnetite doped mesoporous silica nanoparticles (MSNs) in which both internal porous and external surface of MSN are respectively exploited to load two different kinds of cytotoxic cargoes. Notably, an exceptionally high quantity (29%) of poorly hydrophobic drug camptothecin (CPT) is loaded into the nanopores of MSNs; however, in previous reports less than 1% loading efficiency is reported. Following CPT loading in the pores of MSNs, another unconventional but FDA approved arsenic trioxide (ATO) is conjugated onto the surface of nanocomposite via exploiting the thiophilic nature of ATO. Cell inhibition performance of dual drug nanoformulation is significantly higher than single drug formulation, possibly due to additional or synergistic effect, as low as 3μg/ml of double drug nanocarrier were found effective to exterminate cancer cells. Besides drug delivery, the presence of superparamagnetic magnetite nanocrystals additionally empowers this system to be used as a contrast agent in magnetic resonance (MR) imaging for either monitoring diseased tissues or feedback of chemotherapy. We anticipate that the integration of combination therapy with nanotechnology coupled with versatile magnetic manipulation feature may prove a significant step forward toward the development of effective theranostic agents.

Low-density lipoprotein-mimicking nanoparticles for tumor-targeted theranostic applications.

This study introduces multifunctional lipid nanoparticles (LNPs), mimicking the structure and compositions of low-density lipoproteins, for the tumor-targeted co-delivery of anti-cancer drugs and superparamagnetic nanocrystals. Paclitaxel (4.7 wt%) and iron oxide nanocrystals (6.8 wt%, 11 nm in diameter) are co-encapsulated within folate-functionalized LNPs, which contain a cluster of nanocrystals with an overall diameter of about 170 nm and a zeta potential of about -40 mV. The folate-functionalized LNPs enable the targeted detection of MCF-7, human breast adenocarcinoma expressing folate receptors, in T2 -weighted magnetic resonance images as well as the efficient intracellular delivery of paclitaxel. Paclitaxel-free LNPs show no significant cytotoxicity up to 0.2 mg mL(-1) , indicating the excellent biocompatibility of the LNPs for intracellular drug delivery applications. The targeted anti-tumor activities of the LNPs in a mouse tumor model suggest that the low-density lipoprotein-mimetic LNPs can be an effective theranostic platform with excellent biocompatibility for the tumor-targeted co-delivery of various anti-cancer agents.

Taking the temperature of the interiors of magnetically heated nanoparticles.

The temperature increase inside mesoporous silica nanoparticles induced by encapsulated smaller superparamagnetic nanocrystals in an oscillating magnetic field is measured using a crystalline optical nanothermometer. The detection mechanism is based on the temperature-dependent intensity ratio of two luminescence bands in the upconversion emission spectrum of NaYF4:Yb3+, Er3+. A facile stepwise phase transfer method is developed to construct a dual-core mesoporous silica nanoparticle that contains both a nanoheater and a nanothermometer in its interior. The magnetically induced heating inside the nanoparticles varies with different experimental conditions, including the magnetic field induction power, the exposure time to the magnetic field, and the magnetic nanocrystal size. The temperature increase of the immediate nanoenvironment around the magnetic nanocrystals is monitored continuously during the magnetic oscillating field exposure. The interior of the nanoparticles becomes much hotter than the macroscopic solution and cools to the temperature of the ambient fluid on a time scale of seconds after the magnetic field is turned off. This continuous absolute temperature detection method offers quantitative insight into the nanoenvironment around magnetic materials and opens a path for optimizing local temperature controls for physical and biomedical applications.