Superparamagnetic Fe3O4 Nanocrystals Research Articles

An Electrochemiluminescence Sensor Based on Nafion/Magnetic Fe₃O₄ Nanocrystals Modified Electrode for the Determination of Bisphenol A in Environmental Water Samples.

The well-dispersive and superparamagnetic Fe3O4-nanocrystals (Fe3O4-NCs) which could significantly enhance the anodic electrochemiluminescence (ECL) behavior of luminol, were synthesized in this study. Compared to ZnS, ZnSe, CdS and CdTe nanoparticles, the strongest anodic ECL signals were obtained at +1.6 V on the Fe3O4-NCs coated glassy carbon electrode. The ECL spectra revealed that the strong ECL resonance energy transfer occurred between luminol and Fe3O4-NCs. Furthermore, under the optimized ECL experimental conditions, such as the amount of Fe3O4-NCs, the concentration of luminol and the pH of supporting electrolyte, BPA exhibited a stronger distinct ECL quenching effect than its structural analogs and a highly selective and sensitive ECL sensor for the determination of bisphenol A (BPA) was developed based on the Fe3O4-NCs. A good linear relationship was found between the ECL intensity and the increased BPA concentration within 0.01–5.0 mg/L, with a correlation coefficient of 0.9972. The detection limit was 0.66 × 10−3 mg/L. Good recoveries between 96.0% and 105.0% with a relative standard deviation of less than 4.8% were obtained in real water samples. The proposed ECL sensor can be successfully employed to BPA detection in environmental aqueous samples.

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.

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.

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.

Synthesis of uniform and superparamagnetic Fe3O4 nanocrystals embedded in a porous carbon matrix for a superior lithium ion battery anode

A facile and scalable strategy for the synthesis of discrete, homogeneous and small (mostly 5–15 nm) Fe3O4 nanocrystals embedded in a partially graphitized porous carbon matrix was developed, which involved the simple mixing of a metal precursor (Fe(NO3)3·9H2O), a carbon precursor (C6H8O7), and a dispersant (NaCl) in an aqueous solution followed by calcination at 600 °C for 2 h under Ar. As the anode materials for lithium-ion batteries, the Fe3O4/carbon composite with 55.24 wt% Fe3O4 exhibited superior electrochemical performances, such as high reversible lithium storage capacity (834 mA h g−1 at 1 C after 60 cycles, 1 C = 924 mA g−1), high Coulombic efficiency (∼100%), excellent cycling stability, and superior rate capability (588 mA h g−1 at 5 C and 382 mA h g−1 at 10 C). These excellent electrochemical performances could be attributed to the robust porous carbon matrix with a partially graphitized structure for embedding a mass of small Fe3O4 nanocrystals, which not only provided excellent electronic conductivity, short transportation length for both lithium ions and electrons, and enough elastic buffer space to accommodate volume changes upon lithium insertion/extraction, but also could effectively avoid agglomeration of the Fe3O4 nanocrystals and maintain the structural integrity of the electrode during the charge–discharge process. It is believed that the Fe3O4/carbon composite synthesized by the current method is a promising anode material for high energy and power density lithium-ion batteries.

Synthesis of superparamagnetic Fe3O4 nanocrystals in reverse microemulsion at room temperature

Superparamagnetic Fe3O4 nanocrystals were prepared via chemical precipitation in reverse microemulsion at room temperature. The water-in-oil reverse microemulsion system was composed of Triton X-100 as a surfactant, n-butanol as a co-surfactant, cyclohexane as a continuous oil phase, and aqueous phase. Powder X-ray diffraction and transmission electron microscopy results demonstrated that the nanoparticles were pure Fe3O4 with a polyhedral spinel structure and with an average size of 15 nm. Moreover, the sizes of Fe3O4 nanoparticles did not change as water/surfactant mole ratios (W0) increased from 5 to 60. From the magnetometer measurements data, the products exhibited superparamagnetic property with saturation magnetisations of 64·6 emu g−1 at room temperature. Such method was easy and mild, and could synthesise other metal oxide in such experiment situation.

Fabrication and Size‐Selective Bioseparation of Magnetic Silica Nanospheres with Highly Ordered Periodic Mesostructure

AbstractIn this paper, we report a novel synthesis and selective bioseparation of the composite of Fe3O4 magnetic nanocrystals and highly ordered MCM‐41 type periodic mesoporous silica nanospheres. Monodisperse superparamagnetic Fe3O4 nanocrystals were synthesized by thermal decomposition of iron stearate in diol in an autoclave at low temperature. The synthesized nanocrystals were encapsulated in mesoporous silica nanospheres through the packing and self‐assembly of composite nanocrystal–surfactant micelles and surfactant/silica complex. Different from previous studies, the produced magnetic silica nanospheres (MSNs) possess not only uniform nanosize (90 ∼ 140 nm) but also a highly ordered mesostructure. More importantly, the pore size and the saturation magnetization values can be controlled by using different alkyltrimethylammonium bromide surfactants and changing the amount of Fe3O4 magnetic nanocrystals encapsulated, respectively. Binary adsorption and desorption of proteins cytochrome c (cyt c) and bovine serum albumin (BSA) demonstrate that MSNs are an effective and highly selective adsorbent for proteins with different molecular sizes. Small particle size, high surface area, narrow pore size distribution, and straight pores of MSNs are responsible for the high selective adsorption capacity and fast adsorption rates. High magnetization values and superparamagnetic property of MSNs provide a convenient means to remove nanoparticles from solution and make the re‐dispersion in solution quick following the withdrawal of an external magnetic field.

Preparations of bifunctional polymeric beads simultaneously incorporated with fluorescentquantum dots and magnetic nanocrystals

Bifunctional polystyrene beads simultaneously incorporated withfluorescent CdTe quantum dots (Q-dots) and superparamagneticFe3O4 nanocrystals were prepared by a modified mini-emulsion polymerization method, in whichpolymerizable surfactants were used as both phase transfer agent for aqueous colloidalnanoparticles and emulsifier. In addition, silica coating was also introduced toFe3O4 nanocrystals for regulating the internal structure of the composite beads.Transmission electron microscopy, confocal fluorescence microscopy andconventional spectroscopy were used to characterize the composite beads,as well as the polymerizable surfactant-coated CdTe Q-dots and silica-coatedFe3O4 nanoparticles. Different mixing methods were also attempted in order to vary the size ofthe resultant bifunctional beads.

Direct Coprecipitation Route to Monodisperse Dual‐Functionalized Magnetic Iron Oxide Nanocrystals Without Size Selection

Water-soluble monodisperse superparamagnetic Fe3O4 nanocrystals decorated with two distinct functional groups are prepared in a single-step procedure by injecting iron precursors into a refluxing aqueous solution of a polymer ligand, trithiol-terminated poly(methacrylic acid) (PMAA-PTTM), bearing both carboxylate and thiol functionalities. The ratio of carboxylic acid groups in the polymer-protecting ligand to the iron precursors plays a key role in determining the particle size and particle size distribution. The surface functionalities of the ligands allow post-synthesis modification of the materials to produce water-soluble fluorescent magnetic nanocrystals.

Synthesis and characterization of functionalized silica-coated Fe3O4 superparamagnetic nanocrystals for biological applications

Superparamagnetic Fe3O4 nanocrystals were prepared by a chemical coprecipitation method with a thin thickness-adjustable silica layer coated on the surface by hydrolysis of tetraethyl orthosilicate. The silica-coated Fe3O4 nanocrystals were well dispersed and consisted of a 6–7 nm diameter magnetic core and a silica shell about 2 nm thick, according to transmission electron microscopy observations. Fourier transform infrared spectra revealed that amino (–NH2) groups were successfully covalently bonded to the silica-coated Fe3O4 and then carboxyl (–COOH) groups were functionalized to the surface through the reaction of –NH2 and glutaric anhydride. The synthesized nanocrystals have a cubic spinel structure as characterized by x-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. Their magnetic properties were carefully investigated by a SQUID magnetometer. The results showed that the nanocrystals were superparamagnetic and the blocking temperature TB shifted from 131 K down to 92 K after they were coated with a thin nonmagnetic layer, since this layer can effectively suppress the magnetic dipolar interaction between particles; the chemically inert silica layer can limit the outside environment effect on the Fe3O4 cores quite well due to the excellent magnetic reproducibility of the coated nanocrystals after ageing for 7 months at room temperature. In addition, the dependence of their high-field specific magnetization on temperature has a T2 relationship. These functionalized silica-coated Fe3O4 superparamagnetic nanocrystals have great potential in biomagnetic applications.