Superparamagnetic Maghemite Nanoparticles Research Articles

Iron-based compounds coordinated with phospho-polymers as biocompatible probes for dual 31P/1H magnetic resonance imaging and spectroscopy

In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual 31P and 1H MR imaging and spectroscopy (MRI and MRS). The presented probes are composed of biocompatible semitelechelic and multivalent phospho-polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) coordinated with small paramagnetic Fe3+ ions or superparamagnetic maghemite (γ-Fe2O3) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short 1H T1 and T2 relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of 31P relaxation, with the effect being more pronounced for probes based on γ-Fe2O3 and multivalent polymer. While the water-soluble probe having one Fe3+ ion per polymer chain was satisfactorily visualized by both 31P-MRS and 31P-MRI, the probe with multiple Fe3+ ions could only be detected by 31P-MRS, and the probes consisting of γ-Fe2O3 nanoparticles could not be imaged by either technique due to their ultra-short 31P relaxations. In this proof-of-principle study performed on phantoms at a clinically relevant magnetic fields, we demonstrated how the different forms and concentrations of iron affect both the 1H MR signal of the surrounding water molecules and the 31P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.

Green synthesis of superparamagnetic maghemite nanoparticles using banana pseudo-stem: a reusable heterogeneous catalyst for Fenton-like degradation of tetracycline antibiotics

Ferric ions impregnated in banana pseudo stem biomass are converted to superparamagnetic maghemite nanoparticles (MNPs) which activated persulphate towards the degradation of tetracycline antibiotic.

Ferrofluidic aqueous two-phase system with ultralow interfacial tension and micro-pattern formation

Ferrofluids are magnetic liquids known for the patterns they form in external magnetic fields. Typically, the patterns form at the interface between a ferrofluid and another immiscible non-magnetic fluid with a large interfacial tension γ ∼ 10−2 N m−1, leading to large pattern periodicities. Here we show that it is possible to reduce the interfacial tension several orders of magnitude down to ca. γ ∼ 10−6 N m−1 by using two immiscible aqueous phases based on spontaneous phase separation of dextran and polyethylene glycol and the asymmetric partitioning of superparamagnetic maghemite nanoparticles into the dextran-rich phase. The system exhibits classic Rosensweig instability in a uniform magnetic field with a periodicity of ∼200 μm, significantly lower than in traditional systems (∼10 mm). This system paves the way towards the science of pattern formation at the limit of vanishing interfacial tension and ferrofluid applications driven by small external magnetic fields.

Catecholamine Coated Maghemite Nanoparticles for Asphaltene Adsorption/Desorption Process

In this study, a nano-layer polydopamine (PDA) coated superparamagnetic maghemite nanoparticles (MNPs) was applied to investigate the asphaltene adsorption-desorption behavior using a model solution. In this process, Fourier-transform infrared spectrum (FT-IR) spectroscopy of the polydopamine/MNP core/shell (MNP@PDA) before and after asphaltene adsorption was indicated the attachment of asphaltene molecules on the polymeric nano-adsorbent surface. The isotherms and kinetics of the asphaltene adsorption process on the MNP@PDA were studied. The good prediction of asphaltene adsorption by the modified Langmuir model indicated that adsorption occurs on an MNP@PDA surface by multilayer adsorption. Also, within the kinetic models, the double-exponential model can fit the experimental data well. The obtained results revealed that about 90% removal for asphaltene happened within 30 min which can be acceptable. The results of this study showed that natural polymers can be used for surface modification of nanoparticles and use it successfully for asphaltene adsorption from prepared asphaltene-toluene solution.

Magnetic Colloidal Particles in Combinatorial Thin-Film Gradients for Magnetic Resonance Imaging and Hyperthermia

A stable oil-in-water (O/W) magnetic emulsion was prepared by the emulsification of organic ferrofluid in an aqueous media, and its theranostic applications were investigated. The synthesis and characterization of the organic ferrofluid were carried out comprising of superparamagnetic maghemite nanoparticles with oleic acid coating stabilized in octane. Both exhibit spherical morphology with a mean size of 6 nm and 200 nm, respectively, as determined by TEM. Thermogravimetric analysis was carried out to determine the chemical composition of the emulsion. The research work described here is novel and elaborates the fabrication of thin-film gradients with 5, 10, 15, and 20 bilayers by layer-by-layer technique using polydimethyl diallyl ammonium chloride (PDAC) and prepared magnetic colloidal particles. The thin-film gradients were characterized for their roughness, morphology, and wettability. The developed gradient films and colloids were explored in magnetic resonance imaging (MRI) and hyperthermia. T1- and T2-weighted images and their corresponding signal intensities were obtained at 1.5 T. A decreasing trend in signal intensities with an increase in nanoparticle concentration in colloids and along the gradient was observed in T2-weighted images. The hyperthermia capability was also evaluated by measuring temperature rise and calculating specific absorption rates (SAR). The SAR of the colloids at 259 kHz, 327 kHz, and 518 kHz were found to be 156 W/g, 255 W/g, and 336 W/g, respectively. The developed magnetic combinatorial thin-film gradients present a significant potential for the future efficient simultaneous diagnostic and therapeutic bioapplications.

Gd- and Eu-Loaded Iron Oxide@Silica Core-Shell Nanocomposites as Trimodal Contrast Agents for Magnetic Resonance Imaging and Optical Imaging.

Superparamagnetic maghemite core-porous silica shell nanoparticles, γ-Fe2O3@SiO2 (FS), with 50 nm diameter and a 10 nm core, impregnated with paramagnetic complexes b-Ln ([Ln(btfa)3(H2O)2]) (where btfa = 4,4,4-trifluoro-l-phenyl-1,3-butanedione and Ln = Gd, Eu, and Gd/Eu), performing as promising trimodal T1-T2 MRI and optical imaging contrast agents, are reported. These nanosystems exhibit a high dispersion stability in water and no observable cytotoxic effects, witnessed by intracellular ATP levels. The structure and superparamagnetic properties of the maghemite core nanocrystals are preserved upon imbedding the b-Ln complexes in the shell. Hela cells efficiently and swiftly internalize the NPs into the cytosol, with no observable cytotoxicity below a concentration of 62.5 μg mL-1. These nanosystems perform better than the free b-Gd complex as T1 (positive) contrast agents in cellular pellets, while their performance as T2 (negative) contrast agents is similar to the FS. Embedding of the b-Eu complex in the silica pores endows the nanoparticles with strong luminescence properties. The impregnation of gadolinium and europium complexes in a 1:1 ratio afforded a trimodal nanoplatform performing as a luminescent probe and a double T1 and T2 MRI contrast agent even more efficient than b-Gd used on its own, as observed in cell-labeled imaging experiments and MRI cell pellets.

The Effect of Rhodamine-Derived Superparamagnetic Maghemite Nanoparticles on the Motility of Human Mesenchymal Stem Cells and Mouse Embryonic Fibroblast Cells.

Nanoparticles have become popular in life sciences in the last few years. They have been produced in many variants and have recently been used in both biological experiments and in clinical applications. Due to concerns over nanomaterial risks, there has been a dramatic increase in investigations focused on safety research. The aim of this paper is to present the advanced testing of rhodamine-derived superparamagnetic maghemite nanoparticles (SAMN-R), which are used for their nontoxicity, biocompatibility, biodegradability, and magnetic properties. Recent results were expanded upon from the basic cytotoxic tests to evaluate cell proliferation and migration potential. Two cell types were used for the cell proliferation and tracking study: mouse embryonic fibroblast cells (3T3) and human mesenchymal stem cells (hMSCs). Advanced microscopic methods allowed for the precise quantification of the function of both cell types. This study has demonstrated that a dose of nanoparticles lower than 20 µg·cm−2 per area of the dish does not negatively affect the cells’ morphology, migration, cytoskeletal function, proliferation, potential for wound healing, and single-cell migration in comparison to standard CellTracker™ Green CMFDA (5-chloromethylfluorescein diacetate). A higher dose of nanoparticles could be a potential risk for cytoskeletal folding and detachment of the cells from the solid extracellular matrix.

Combined antitumor effect of surface-modified superparamagnetic maghemite nanoparticles and a vitamin E derivative on experimental Walker-256 mammary gland carcinosarcoma

In a search for efficient anti-tumor agent, silica-coated superparamagnetic nanoparticles were designed and used in combination with vitamin E derivative as a potential new tool for anticancer treatment. The particles were characterized by numerous techniques, such as transmission electron microscopy and dynamic light scattering to determine the particle morphology and size both in dry state and water, atomic absorption spectroscopy to analyze the iron content, Fourier-transform infrared spectroscopy to confirm the presence of the functional groups, and vibrating sample magnetometry to determine the magnetic properties and content of maghemite. The next aim was to assess effect of the nanoparticles on suppression of experimental mammary gland carcinosarcoma W-256. Strong antitumor effect was achieved only with combined application of γ-Fe2O3@SiO2 and acetate derivative of α-tocopherol (Toc-6-Ac) resulting in 58% of tumor volume reduction. The results were compared with those obtained with poly(N,N-dimethylacrylamide)-coated iron oxide particles described earlier.

Apple pectin supported superparamagnetic (γ-Fe2O3) maghemite nanoparticles with antimicrobial potency

Magnetic nanoparticles are themselves a fascinating world due to their various applications in different fields mainly biomedical, catalysis, storage devices and many more. Till now magnetites have been explored extensively through different routes whereas another oxide of iron that is maghemite needs attention and yet to be discovered in different aspects. Here we show the simple, facile and less time consuming method to synthesize superparamagnetic maghemite nanoparticles. The highlights and novelty of the synthesis are marked by the use of sodium borohydride to obtain small sized iron oxide nanoparticles starting from a transition metal complex and further stabilizing them with a polysaccharide that is apple pectin. The maghemite nanoparticles thus synthesized, are characterized by SEM, TEM and XRD whereas, pectin binding with nanoparticles is confirmed by FTIR. The size of nanoparticles obtained is between 2 and 6 nm. The phase clarity of maghemites has been derived using Mossbauer spectra. Along with this, their antimicrobial behavior has also been studied using four different bacterial strains P. aerugenosa, S. aureus B. cereus and S. typhii. The nanoparticles were found to inhibit the growth of bacteria. The present work proposes green synthesis of maghemite nanoparticles in water as solvent and supports waste management by using polysaccharide obtained from apple peel.

Toward highly effective and easily separable halloysite-containing adsorbents: The effect of iron oxide particles impregnation and new insight into As(V) removal mechanisms

Abstract Halloysite containing composites impregnated with Fe oxide particles (10 and 25% loading) were synthesized by co-precipitation method. The obtained uncalcined and calcined materials were tested for aqueous As(V) removal in different experimental conditions. The experiments were designed to test both the material’s adsorption capacity and the mechanisms responsible for As(V) removal. The XRD, Mossbauer spectroscopy, FTIR and SEM results revealed that Fe oxides formed during the synthesis were superparamagnetic maghemite (γ-Fe 2 O 3 ) nanoparticles with approximate size of 20 nm. Their presence as well as their homogenous distribution induced a strong response of the composites to the applied magnetic field, enabling magnetic separation of the adsorbents. The impregnation with Fe oxide particles resulted in an increase of surface area and changes of porosity. The As(V) adsorption studies revealed, that the material impregnated with Fe oxide exhibited higher adsorption capacity, than the starting mineral sample. Moreover the highest adsorption capacity of 180 mmol/kg was noticed for calcined composites. In order to better understand the As(V) adsorption mechanisms, the effect of pH and ionic strength was investigated as well as desorption, and the XPS studies were applied. The results revealed the formation of inner-sphere complexes between As(V) and composites surface as well as As(V) reduction coupled with Fe(II) oxidation as the main removal mechanisms. The chemisorption had a significant impact on the mineral support structure by increasing its stiffness as indicated by Mossbauer spectroscopy. The studied composites showed high stability in a broad pH range, measured as As, Si, Al and Fe release, which enables their use in environmental applications.

基于磁性质的药物递送系统

There has been unprecedented progress in the development of biomedical nanotechnology and nanomaterials over the past few decades, and nanoparticle-based drug delivery systems (DDSs) have great potential for clinical applications. Among these, magnetic drug delivery systems (MDDSs) based on magnetic nanoparticles (MNPs) are attracting increasing attention owing to their favorable biocompatibility and excellent multifunctional loading capability. MDDSs primarily have a solid core of superparamagnetic maghemite (γ-Fe2O3) or magnetite (Fe3O4) nanoparticles ranging in size from 10 to 100 nm. Their surface can be functionalized by organic and/or inorganic modification. Further conjugation with targeting ligands, drug loading, and MNP assembly can provide complex magnetic delivery systems with improved targeting efficacy and reduced toxicity. Owing to their sensitive response to external magnetic fields, MNPs and their assemblies have been developed as novel smart delivery systems. In this review, we first summarize the basic physicochemical and magnetic properties of desirable MDDSs that fulfill the requirements for specific clinical applications. Secondly, we discuss the surface modifications and functionalization issues that arise when designing elaborate MDDSs for future clinical uses. Finally, we highlight recent progress in the design and fabrication of MNPs, magnetic assemblies, and magnetic microbubbles and liposomes as MDDSs for cancer diagnosis and therapy. Recently, researchers have focused on enhanced targeting efficacy and theranostics by applying step-by-step sequential treatment, and by magnetically modulating dosing regimens, which are the current challenges for clinical applications.

Lead (Pb2+) and copper (Cu2+) remediation from water using superparamagnetic maghemite (γ-Fe2O3) nanoparticles synthesized by Flame Spray Pyrolysis (FSP)

Superparamagnetic maghemite (γ-Fe2O3) nanoparticles of controllable morphology were successfully synthesized using a flame spray pyrolysis (FSP) technique. Their physico-chemical properties, size, morphology, and surface chemistries were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), selected area electron diffraction patterns (SAED), SEM-EDX, scanning electron microscopy (SEM), and pHZPC(6.3). Elemental contents before and after adsorption were identified using energy dispersive X-ray fluorescence (ED-XRF), energy dispersive X-ray analysis (EDX) and elemental mapping. Surface area (SBET 79.35m2/g) and size distribution analyses were conducted using a surface area analyzer and dynamic light scattering (DLS), respectively. The magnetic moment (44.5 at 300K and 50.16 at 2K) was determined using a physical properties measurement system (PPMS). The first adsorption study using γ-Fe2O3 nanoparticles synthesized by FSP to successfully remediate Pb2+ and Cu2+ from water is reported. Batch adsorption studies were carried out. An optimum pH of 5.0 was studied for Pb2+ and Cu2+ removal. Pb2+ and Cu2+ removal mechanisms by these maghemite nanoparticles were presented. The adsorption of Pb2+ and Cu2+ was highly pH-dependent. The metal ion uptake was mainly governed by electrostatic attractions. Sorption kinetic data followed the pseudo-second-order model. The Freundlich, Langmuir, Redlich–Peterson, Radke and Sips adsorption isotherm models were applied to interpret equilibrium data. The Freundlich and Langmuir isotherm equations best fit the respective equilibrium data for Pb2+ and Cu2+. The maximum Langmuir adsorption capacities of these maghemite nanoparticles were 68.9mg/g at 45°C for Pb2+ and 34.0mg/g at 25 °C for Cu2+. Thus, these maghemite nanoparticles made by FSP were readily prepared, characterized and showed promise for remediating heavy metal ions from aqueous solutions.

Rhodamine bound maghemite as a long-term dual imaging nanoprobe of adipose tissue-derived mesenchymal stromal cells.

In the last few years, magnetically labeled cells have been intensively explored, and non-invasive cell tracking and magnetic manipulation methods have been tested in preclinical studies focused on cell transplantation. For clinical applications, it is desirable to know the intracellular pathway of nanoparticles, which can predict their biocompatibility with cells and the long-term imaging properties of labeled cells. Here, we quantified labeling efficiency, localization, and fluorescence properties of Rhodamine derivatized superparamagnetic maghemite nanoparticles (SAMN-R) in mesenchymal stromal cells (MSC). We investigated the stability of SAMN-R in the intracellular space during a long culture (20days). Analyses were based on advanced confocal microscopy accompanied by atomic absorption spectroscopy (AAS) and magnetic resonance imaging. SAMN-R displayed excellent cellular uptake (24h of labeling), and no toxicity of SAMN-R labeling was found. 83% of SAMN-R nanoparticles were localized in lysosomes, only 4.8% were found in mitochondria, and no particles were localized in the nucleus. On the basis of the MSC fluorescence measurement every 6days, we also quantified the continual decrease of SAMN-R fluorescence in the average single MSC during 18days. An additional set of analyses showed that the intracellular SAMN-R signal decrease was minimally caused by fluorophore degradation or nanoparticles extraction from the cells, main reason is a cell division. The fluorescence of SAMN-R nanoparticles within the cells was detectable minimally for 20days. These observations indicate that SAMN-R nanoparticles have a potential for application in transplantation medicine.

Efficient penetration of ceric ammonium nitrate oxidant-stabilized gamma-maghemite nanoparticles through the oval and round windows into the rat inner ear as demonstrated by MRI.

We aimed to evaluate the magnetic resonance imaging (MRI) contrast effect and delivery efficiency through the middle ear into the inner ear using novel super-paramagnetic maghemite (γ-Fe2 O3 ) nanoparticles (NPs) generated using ceric ammonium nitrate (CAN)-mediated oxidation of Fe3 O4 NPs (CAN-γ-Fe2 O3 NPs). The CAN-γ-Fe2O3 NPs, having hydrodynamic diameters of 50-60 nm and potentials of +55.2 mV, displayed super-paramagnetic behavior characterized by a saturation magnetization Ms of 75.2 emu/g NPs. The r1 and r2* relaxivity (curve slopes) values were 0.0015 and 189 mmol-1 s-1 , respectively, indicating strong T2* relaxation maghemite-based NPs. The CAN-γ-Fe2 O3 NPs were stable in the 7.0 T magnetic field. At 3 h after the tympanic medial wall administration, the NPs had significantly located to the cochlea and vestibule. The signal started to recover at 6 h in the ipsilateral cochlea and by 2 d in the vestibule post-administration. There was no difference in the signal intensity between the left and right ears on the 14th d. Prussian blue staining for iron demonstrated NP distribution in the inner ear tissue. The novel CAN-γ-Fe2 O3 NPs are a strong MRI T2 contrast agent and penetrated the round and oval windows and have potential application in the molecular imaging of the inner ear. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1883-1891, 2017.

Superparamagnetic nanoparticles encapsulated in lipid vesicles for advanced magnetic hyperthermia and biodetection

A multifunctional nanocomposite formed by superparamagnetic maghemite nanoparticles of 12.8 ± 1.7 nm diameter encapsulated in lipid unilamellar vesicles (i.e., magnetoliposomes) was prepared using size exclusion chromatography (SEC). The quality of the synthesized nanoparticles was characterized by transmission electron microscopy and X-ray diffraction measurements. Using a modified Langevin model, we analyzed the magnetic measurement data. We found that the SEC prepared magnetoliposomes possess superparamagnetic characteristics. We also performed calorimetric based magnetic hyperthermia measurement to quantify field dependent heating efficiency of the obtained magnetoliposomes. A heating efficiency of ∼160 W/g at 800 Oe and 310 kHz was obtained. Finally, we used magnetoreactance-based biodetection to explore the effect of magnetoliposomes on magneto-impedance (MI) and magneto-reactance (MX) ratios. Compared to pure vesicles, magnetoliposomes were found to increase the MI and MX ratios by ∼1.0% and 4.5%, respectively. Together, our magnetic hyperthermia and magneto-detection measurements indicate that our SEC prepared magnetoliposomes exhibit good qualities for hyperthermia and biosensing applications.

The Effect of Temperature on Synthesis and Stability of Superparamagnetic Maghemite Nanoparticles Suspension

Maghemite (γ-Fe2O3) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM) and thermogravimetryanalysis (TGA). The stability of the maghemite nanoparticles suspension was studied at different pH and time of storage by dynamic light scattering (DLS) and zeta potential measurements. The XRD patterns confirmed that the particles were maghemite. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with good thermal stability. The increasing of temperature in the synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability and more stable maghemite nanoparticle suspension.

Preparation of superparamagnetic maghemite (γ-Fe2O3) nanoparticles by wet chemical route and investigation of their magnetic and dielectric properties

Maghemite (γ-Fe2O3) nanoparticles have been synthesized using a wet chemical route, optimizing the reaction time, PH value and size of the crystallite during synthesis. The Powder X-ray diffraction (XRD) measurements confirmed the presence of an impurity free maghemite phase in our sample with an average crystallite size of 16 nm as calculated from the Debye–Scherrer equation. In physical characterization, the room temperature hysteresis (M−H loop) and blocking temperature (as observed from the M-T plot) revealed that the particles are in the superparamagnetic phase at room temperature. Dielectric behaviour of γ-Fe2O3 with respect to the variation of frequency and temperature was also performed. At room temperatures, we observe a decaying behaviour of both dielectric constant (έ) and tangent looses (tanδ) at smaller frequencies while at higher frequencies both saturate to smaller constant values. In temperature dependent dielectric properties we notice that the dielectric constant (both real and imaginary parts) show an increasing trend with increasing temperatures but an overall slower enhancement at elevated frequencies. The former effect can be attributed to the possible delocalization of impurities at higher temperatures while the latter effect can be explained as an inability of the electric dipole moments to respond at higher frequencies.

Preparation and Physical Characterizations of Superparamagnetic Maghemite Nanoparticles

Superparamagnetic maghemite nanoparticles were prepared by chemical co-precipitation, followed by a temperate oxidation stage, and investigated using FE-SEM, XRD, TGA, VSM, and Mossbauer spectroscopy. Through SEM image and XRD analysis, its average particle size was found to be 13.9 nm. While VSM magnetic measurement showed typical superparamagnetic behavior at room temperature, Mossbauer spectroscopic investigation revealed that non-vanishing magnetic hyperfine structure were retained. Cation distribution estimated from Mossbauer spectroscopy confirmed the formation of maghemite nanophase in the sample.

Phase and surface area studies of maghemite nanoparticles dispersed in silica gel

First, the superparamagnetic maghemite nanoparticles were synthesised using Massart's procedure. Then, the nanocomposites of the synthesised maghemite nanoparticles and silica were produced by dispersing the as-synthesised maghemite nanoparticles into the silica xerogel prepared by sol–gel technique. The system was then heated for 3 days at 140°C. The phase analysis performed using X-ray diffraction confirmed that the as-synthesised nanoparticles and the nanoparticles within the silica gel were maghemite. Surface characteristic of the nanocomposite was evaluated by N2 adsorption. The ‘pure’ silica gel and maghemite nanoparticles showed high values of surface area (150–160 m2 g−1), while the surface area of nanocomposite was less than 40 m2 g−1. This was probably due to the formation of dense structures caused by incorporation of maghemite nanoparticles within the pores of silica gel. The pore width increased with increasing content of maghemite nanoparticles.

Molecular insights of oxidation process of iron nanoparticles: spectroscopic, magnetic, and microscopic evidence.

Oxidation behavior of nano-Fe(0) particles in an anoxic environment was determined using different state-of-the-art analytical approaches, including high resolution transmission electron microscopy (HR-TEM) combined with energy filtered transmission electron microscopy (EFTEM), X-ray absorption spectroscopy (XAS), and magnetic measurements. Oxidation in controlled experiments was compared in standard double distilled (DD) water, DD water spiked with trichloroethene (TCE), and TCE contaminated site water. Using HR-TEM and EFTEM, we observed a surface oxide layer (∼3 nm) formed immediately after the particles were exposed to water. XAS analysis followed the dynamic change in total metallic iron concentration and iron oxide concentration for the experimental duration of 35 days. The metallic iron concentration in nano-Fe(0) particles exposed to water, was ∼40% after 35 days; in contrast, the samples containing TCE were reduced to ∼15% and even to nil in the case of TCE contaminated site water, suggesting that the contaminants enhance the oxidation of nano-Fe(0). Frequency dependence measurements confirmed the formation of superparamagnetic particles in the system. Overall, our results suggest that nano-Fe(0) oxidized via the Fe(0) - Fe(OH)2 - Fe3O4 - (γ-Fe2O3) route and the formation of superparamagnetic maghemite nanoparticles due to disruption of the surface oxide layer.