Synthesis,characterization, and in vitro biological evaluation of highly stable diversely functionalized superparamagnetic iron oxide nanoparticles

In this article, we report the design and synthesis of a series of well-dispersed superparamagnetic iron oxide nanoparticles (SPIONs) using chitosan as a surface modifying agent to develop a potential T ₂ contrast probe for magnetic resonance imaging (MRI). The amine, carboxyl, hydroxyl, and thiol functionalities were introduced on chitosan-coated magnetic probe via simple reactions with small reactive organic molecules to afford a series of biofunctionalized nanoparticles. Physico-chemical characterizations of these functionalized nanoparticles were performed by TEM, XRD, DLS, FTIR, and VSM. The colloidal stability of these functionalized iron oxide nanoparticles was investigated in presence of phosphate buffer saline, high salt concentrations and different cell media for 1 week. MRI analysis of human cervical carcinoma (HeLa) cell lines treated with nanoparticles elucidated that the amine-functionalized nanoparticles exhibited higher amount of signal darkening and lower T ₂ relaxation in comparison to the others. The cellular internalization efficacy of these functionalized SPIONs was also investigated with HeLa cancer cell line by magnetically activated cell sorting (MACS) and fluorescence microscopy and results established selectively higher internalization efficacy of amine-functionalized nanoparticles to cancer cells. These positive attributes demonstrated that these nanoconjugates can be used as a promising platform for further in vitro and in vivo biological evaluations.     

Cell viability and MRI performance of highly efficient polyol-coated magnetic nanoparticles

This work aimed at determining conditions that would allow us to control the size of the NPs and create a system with characteristics apt for biomedical applications. We describe a comprehensive study on the synthesis and physical characterization of two highly sensitive sets of triethylene glycol (TREG) and polyethylene glycol (PEG)-coated superparamagnetic iron oxide nanoparticles (SPIONs) to be evaluated for use as magnetic resonance (MR) contrast agents. The ferrofluids demonstrated excellent colloidal stability in deionized water at pH 7.0 as indicated by dynamic light scattering (DLS) data. The magnetic relaxivities, r ₂, were measured on a 1.5 T clinical MRI instrument. Values in the range from 205 to 257 mM^?1 s^?1 were obtained, varying proportionally to the SPIONs’ sizes and coating nature. Further in vitro cell viability tests and in vivo biodistribution analyses of the intravenously administered nanoparticles showed that the prepared systems have good biocompatibility and migrate to several organs, mainly the meninges, spleen, and liver. Based on these results, our findings demonstrated the potential utility of these nanosystems as clinical contrast agents for MR imaging.     

Synthesis of amino-group functionalized superparamagnetic iron oxide nanoparticles and applications as biomedical labeling probes

Superparamagnetic iron oxide (SPIO) nanoparticles were synthesized by coprecipitation technique and further functionalized with amino-group to obtain amino-group functionalized (amino-SPIO) nanoparticles. The X-ray diffraction results reveal the structure of amino-SPIO nanoparticles, from which the average iron core diameter is approximately 10 nm by calculation; while Zetasizer reveals their hydrodynamic diameter are mainly distributed in the range of 40?C60 nm. These nanoparticles can be taken up by liver tissue, resulting in dramatically darkening of liver tissue under T2-magnetic resonance imaging (MRI). The spin?Cspin relaxivity coefficient of these nanoparticles is 179.20 mM^?1 s^?1 in a 1.5 T magnetic resonance system. In addition, amino-SPIO nanoparticles were conjugated to Tat (FITC) peptide and incubated with neural stem cells in vitro, the authors can detect the positive-labeling (labeled) neural stem cells showing green fluorescence, which indicates Tat (FITC) peptide-derivated amino-SPIO nanoparticles are able to enter cells. Furthermore, it was also find significant negative T2 contrast enhancement when compared with the non-nanoparticles-labeled neural stem cells in T2-weighted MRI. The amino-SPIO nanoparticles show promising potential as a new type of labeling probes, which can be used in magnetic resonance-enhanced imaging and fluorescence diagnosis.     

MRI contrast agent for molecular imaging of the HER2/neu receptor using targeted magnetic nanoparticles

In this study, Trastuzumab modified Magnetic Nanoparticles (TMNs) were prepared as a new contrast agent for detecting HER2 (Human epidermal growth factor receptor-2) expression tumors by magnetic resonance imaging (MRI). TMNs were prepared based on iron oxide nanoparticles core and Trastuzumab modified dextran coating. The TMNs core and hydrodynamic size were determined by transmission electron microscopy and dynamic light scattering. TMNs stability and cytotoxicity were investigated. The ability of TMNs for HER2 detection were evaluated in breast carcinoma cell lines (SKBr3 and MCF7 cells) and tumor-bearing mice by MRI and iron uptake determination. The particles core and hydrodynamic size were 9 ± 2.5 and 41 ± 15 nm (size range: 15?C87 nm), respectively. The molar antibody/nanoparticle ratio was 3.1?C3.5. TMNs were non-toxic to the cells below the 30 ??g (Fe)/mL concentration and good stable up to 8 weeks in PBS buffer. TMNs could detect HER2 oncogenes in the cells surface with imagable contrast by MRI. The invivo study in mice bearing tumors indicated that TMNs possessed a good diagnostic ability as HER2 specific contrast agent by MRI. TMNs were demonstrated to be able to selectively accumulate in the tumor cells, with a proper signal enhancement in MRI T2 images. So, the complex may be considered for further investigations as an MRI contrast agent for detection of HER2 expression tumors in human.     

Comparative analysis of the 1H NMR relaxation enhancement produced by iron oxide and core-shell iron-iron oxide nanoparticles

Physicochemical and magnetorelaxometric characterization of the colloidal suspensions consisting of Fe-based nanoparticles coated with dextran have been carried out. Iron oxide and iron core/iron oxide shell nanoparticles were obtained by laser-induced pyrolysis of Fe(CO)₅ vapours. Under different magnetic field strengths, the colloidal suspension formed by iron oxide nanoparticles showed longitudinal (R₁) and transverse (R₂) nuclear magnetic relaxation suspension (NMRD) profiles, similar to those previously reported for other commercial magnetic resonance imaging (MRI) contrast agents. However, colloidal suspension formed by ferromagnetic iron-core nanoparticles showed a strong increase of the R₁ values at low applied magnetic fields and a strong increase of the R₂ measured at high applied magnetic field. This behaviour was explained considering the larger magnetic aggregate size and saturation magnetization values measured for this sample, 92 nm and 31 emu/g Fe, respectively, with respect to those measured for the colloidal suspensions of iron oxide nanoparticles (61 nm and 23 emu/g Fe). This suspension can be used both as T₁ and T₂ contrast agent.     

Characterization of PEI-coated superparamagnetic iron oxide nanoparticles for transfection: Size distribution,colloidal properties and DNA interaction

Superparamagnetic iron oxide nanoparticles (SPIONs) were coated with polyethylenimine. Here, we briefly describe the synthesis as well as DNA:PEI:SPION complexes and the characterization of the compounds according to their particle size, ζ-potential, morphology, DNA complexing ability, magnetic sedimentation, and colloidal stability. PEI coating of SPIONs led to colloidally stable beads even in high salt concentrations over a wide pH range. DNA plasmids and PCR products encoding for green fluorescent protein were associated with the described beads. The complexes were added to cells and exposed to permanent and pulsating magnetic fields. Presence of these magnetic fields significantly increased the transfection efficiency.     

Effect of chain length and electrical charge on properties of ammonium-bearing bisphosphonate-coated superparamagnetic iron oxide nanoparticles: formulation and physicochemical studies

Bisphosphonates BP molecules have shown to be efficient for coating superparamagnetic iron oxide particles. In order to clarify the respective roles of electrical charge and the length of the molecules, bisphosphonates with one or two ammonium moieties with an intermediate aliphatic group of 3, 5 or 7 carbons were synthesized and iron oxide nanoparticles coated. The evaluation on their iron core properties was made by transmission electron microscopy (TEM), nuclear magnetic relaxation dispersion (NMRD) profiles and Mössbauer spectra. The core size is close to 5 nm, with a global superparamagnetic behaviour modified by a paramagnetic Fe-based layer, probably due to surface crystal alteration. The hydrodynamic sizes increase slightly with aliphatic chain length (from 9.8 to 18.6 nm). The presence of one or two ammonium group(s) lowers the negative electrophoretic mobility up to bear zero values but reduces their colloidal stability. These BP-coated iron oxide nanoparticles are promising Magnetic Resonance Imaging (MRI) contrast agents.     

Cellular uptake of folate-conjugated lipophilic superparamagnetic iron oxide nanoparticles

We prepared five folate-conjugated lipophilic superparamagnetic iron oxide nanoparticles (F₅-Liposuperparamagnetic iron oxide nanoparticles(SPIONs), 5.5 and 11 nm) and investigated their cellular uptake with KB cells, which is one of the representative folate-receptor over-expressing human epidermoid carcinoma cells, using MRI. The cellular uptake tests with the respective 5.5 and 11 nm F₅-LipoSPIONs at a fixed particle concentration showed appreciable amount of receptor-mediated uptakes and the specificity was higher in 5.5 nm SPIONs, due to its higher folic acid (FA) density, without inhibition. However, the numbers of the particles taken up under FA inhibition were similar, irrespective of their sizes.     

Multifunctional iron platinum stealth immunomicelles: targeted detection of human prostate cancer cells using both fluorescence and magnetic resonance imaging

Superparamagnetic iron oxide nanoparticles (SPIONs) are the most common type of contrast agents used in contrast agent-enhanced magnetic resonance imaging (MRI). Still, there is a great deal of room for improvement, and nanoparticles with increased MRI relaxivities are needed to increase the contrast enhancement in MRI applied to various medical conditions including cancer. We report the synthesis of superparamagnetic iron platinum nanoparticles (SIPPs) and subsequent encapsulation using PEGylated phospholipids to create stealth immunomicelles (DSPE-SIPPs) that can be specifically targeted to human prostate cancer cell lines and detected using both MRI and fluorescence imaging. SIPP cores and DSPE-SIPPs were 8.5 ± 1.6 nm and 42.9 ± 8.2 nm in diameter, respectively, and the SIPPs had a magnetic moment of 120 A m²/kg iron. J591, a monoclonal antibody against prostate specific membrane antigen (PSMA), was conjugated to the DSPE-SIPPs (J591-DSPE-SIPPs), and specific targeting of J591-DSPE-SIPPs to PSMA-expressing human prostate cancer cell lines was demonstrated using fluorescence confocal microscopy. The transverse relaxivity of the DSPE-SIPPs, measured at 4.7 Tesla, was 300.6 ± 8.5 s^?1 mM^?1, which is 13-fold better than commercially available SPIONs (23.8 ± 6.9 s^?1 mM^?1) and ~3-fold better than reported relaxivities for Feridex^® and Resovist^®. Our data suggest that J591-DSPE-SIPPs specifically target human prostate cancer cells in vitro, are superior contrast agents in T ₂-weighted MRI, and can be detected using fluorescence imaging. To our knowledge, this is the first report on the synthesis of multifunctional SIPP micelles and using SIPPs for the specific detection of prostate cancer.     

Structural and magnetic studies of the Zn-substituted magnesium ferrite chromate

The formation of iron oxide nanoparticles in course of a sol-gel preparation process was traced by UV/Vis and ⁵⁷Fe Mössbauer absorption spectroscopy. Samples were extracted at different stages of the reaction. While spectra measured on samples extracted at low reactor temperatures showed the starting materials Fe(acac)₃ diluted in benzyl alcohol undergoing slow paramagnetic relaxation, a sample extracted at a reactor temperature of 180 °C gave clear evidence for emerging iron oxide nanoparticles. A prolonged stay at 200 °C results in a complete transformation from Fe(acac)₃ to maghemite nanoparticles.     

Nanosized cancer cell-targeted polymeric immunomicelles loaded with superparamagnetic iron oxide nanoparticles

Stable 30–50 nm polymeric polyethylene glycol–phosphatidylethanolamine (PEG–PE)-based micelles entrapping superparamagnetic iron oxide nanoparticles (SPION) have been prepared. At similar concentrations of SPION, the SPION-micelles had significantly better magnetic resonance imaging (MRI) T2 relaxation signal compared to ‘plain’ SPION. Freeze-fracture electron microscopy confirmed SPION entrapment in the lipid core of the PEG–PE micelles. To enhance the targeting capability of these micelles, their surface was modified with the cancer cell-specific anti-nucleosome monoclonal antibody 2C5 (mAb 2C5). Such mAb 2C5-SPION immunomicelles demonstrated specific binding with cancer cells in vitro and were able to bring more SPION to the cancer cells thus demonstrating the potential to be used as targeted MRI contrast agents for tumor imaging.     

Size-controlled synthesis of superparamagnetic iron oxide nanoparticles and their surface coating by gold for biomedical applications

The size mono-dispersity, saturation magnetization, and surface chemistry of magnetic nanoparticles (NPs) are recognized as critical factors for efficient biomedical applications. Here, we performed modified water-in-oil inverse nano-emulsion procedure for preparation of stable colloidal superparamagnetic iron oxide NPs (SPIONs) with high saturation magnetization. To achieve mono-dispersed SPIONs, optimization process was probed on several important factors including molar ratio of iron salts [Fe³⁺ and Fe²⁺], the concentration of ammonium hydroxide as reducing agent, and molar ratio of water to surfactant. The biocompatibility of the obtained NPs, at various concentrations, was evaluated via MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay and the results showed that the NPs were non-toxic at concentrations <0.1 mg/mL. Surface functionalization was performed by conformal coating of the NPs with a thin shell of gold (∼4 nm) through chemical reduction of attached gold salts at the surface of the SPIONs. The Fe₃O₄ core/Au shell particles demonstrate strong plasmon resonance absorption and can be separated from solution using an external magnetic field. Experimental data from both physical and chemical determinations of the changes in particle size, surface plasmon resonance optical band, phase components, core–shell surface composition, and magnetic properties have confirmed the formation of the mono-dispersed core–shell nanostructure.     

Colloidal Flower‐Shaped Iron Oxide Nanoparticles: Synthesis Strategies and Coatings

The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self‐assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi‐core nanoparticles are determined. In addition, a self‐consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower‐shaped iron oxide assemblies in the size range 25–100 nm are examined. The routes are based on the partial oxidation of Fe(OH)₂, polyol‐mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long‐term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi‐core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower‐shaped nanoparticles.     

Encapsulation of a proteasome inhibitor with gold-polysaccharide nanocarriers

Groundwater remediation using iron oxide and zero-valent iron nanoparticles (NPs) can be effective, but is limited in many applications due to the NP strong retention in groundwater-saturated porous media after injection, the passivation of the porous surface, and the high cost of nanomaterials versus macro scale iron. In this study, we investigated transport of bare and polymer-coated 2-line ferrihydrite NPs (30–300 nm) in saturated aquifer sediments. The influence of poly(acrylic acid) (PAA) polymer coatings was studied on the colloidal stability and transport in sediments packed column tests simulating groundwater flow in saturated sediments. In addition, the influence of calcium cations was investigated by transport measurements using sediments with calcium concentrations in the aqueous phase ranging from 0.5 (typical for most sediments) to 2 mM. Measurements were also made of zeta potential, hydrodynamic diameter, polymer adsorption and desorption properties, and bio-availability of PAA-coated NPs. We found that NP transport through the saturated aquifer sediments was improved by PAA coating and that the transport properties could be tuned by adjusting the polymer concentration. We further discovered that PAA coatings enhanced NP transport, compared to bare NPs, in all calcium-containing experiments tested, however, the presence of calcium always exhibited a negative effect on NP transport. In tests of bioavailability, the iron reduction rate of the coated and bare NPs by Geobacter sulfurreducens was the same, which shows that the PAA coating does not significantly reduce NP Fe(III) bioavailability. Our results demonstrate that much improved transport of iron oxide NP can be achieved in saturated aquifer sediments by introducing negatively charged polyelectrolytes and optimizing polymer concentrations, and furthermore, these coated NPs retain their bioavailability that is needed for applications in bio-environmental remediation.     

Toxicity of superparamagnetic iron oxide nanoparticles: Research strategies and implications for nanomedicine

Superparamagnetic iron oxide nanoparticles （SPIONs） are one of the most versatile and safe nanoparticles in a wide variety of biomedical applications. In the past decades, considerable efforts have been made to investigate the potential adverse biological effects and safety issues associated with SPIONs, which is essential for the development of next-generation SPIONs and for continued progress in translational research. In this mini review, we summarize recent developments in toxicity studies on SPIONs, focusing on the relationship between the physicochemical properties of SPIONs and their induced toxic biological responses for a better toxicological understanding of SPIONs.     

Dispersions of silica nanoparticles in ionic liquids investigated with advanced rheology

The colloidal stabilities of dispersions of unmodified and surface-functionalized SiO₂ nanoparticles in hydrophobic and hydrophilic imidazolium-based ionic liquids were studied with advanced rheology at three temperatures (25, 100, and 200 °C). The rheological behavior of the dispersions was strongly affected by the ionic liquids hydrophilicity, by the nanoparticles surface, by the concentration of the nanoparticles in the dispersion as well as by the temperature. The unmodified hydrophilic nanoparticles showed a better compatibility with the hydrophilic ionic liquid. The SiO₂ surface functionalization with hydrophobic groups clearly improved the colloidal stability of the dispersions in the hydrophobic ionic liquid. The temperature increase was found to lead to a destabilization in all studied systems, especially at higher concentrations. The results of this study imply that ionic liquids with tailored properties could be used in absorbers directly after reactors for gas-phase synthesis of nanoparticles or/and as solvents for their further surface functionalization without agglomeration or aggregation.     

Iron oxide nanoparticle synthesis in aqueous and membrane systems for oxidative degradation of trichloroethylene from water

The potential for using hydroxyl radical (OH^?) reactions catalyzed by iron oxide nanoparticles (NPs) to remediate toxic organic compounds was investigated. Iron oxide NPs were synthesized by controlled oxidation of iron NPs prior to their use for contaminant oxidation (by H₂O₂ addition) at near-neutral pH values. Cross-linked polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) microfiltration membranes were prepared by in situ polymerization of acrylic acid inside the membrane pores. Iron and iron oxide NPs (80–100 nm) were directly synthesized in the polymer matrix of PAA/PVDF membranes, which prevented the agglomeration of particles and controlled the particle size. The conversion of iron to iron oxide in aqueous solution with air oxidation was studied based on X-ray diffraction, Mössbauer spectroscopy and BET surface area test methods. Trichloroethylene (TCE) was selected as the model contaminant because of its environmental importance. Degradations of TCE and H₂O₂ by NP surface generated OH^? were investigated. Depending on the ratio of iron and H₂O₂, TCE conversions as high as 100 % (with about 91 % dechlorination) were obtained. TCE dechlorination was also achieved in real groundwater samples with the reactive membranes.     

HoF3 and DyF3 Nanoparticles as Contrast Agents for High‐Field Magnetic Resonance Imaging

Clinical contrast agents (CAs) currently used in magnetic resonance imaging (MRI) at low fields are less effective at high magnetic fields. The development of new CAs is mandatory to improve diagnostic capabilities of the new generation of high field MRI scanners. The purpose of this study is to synthesize uniform, water dispersible LnF₃ (Ln = Ho, Dy) nanoparticles (NPs) and to evaluate their relaxivity at high magnetic field (9.4 T) as a function of size and composition. Two different types of HoF₃ NPs are obtained by homogeneous precipitation in ethylene glycol at 120 °C. The use of holmium acetate as holmium precursor leads to rhombus‐like nanoparticles, while smaller, ellipsoid‐like nanoparticles are obtained when nitrate is used as the holmium salt. To explain this behavior, the mechanism of formation of both kinds of particles is analyzed in detail. Likewise, rhombus‐like DyF₃ nanoparticles are prepared following the same method as for the rhombus‐like HoF₃ nanoparticles. We have found, to the best of knowledge, the highest transverse relaxivity values at 9.4 T described in the literature for this kind of CAs. Finally, the LnF₃ NPs have shown negligible cytotoxicity for C6 rat glioma cells for concentrations up to 0.1 mg mL^?1.     

EPR Detection of Possible Superparamagnetic Polyiron Nanoparticles and Free Radicals in the Blood Serum of Patients with Homozygous β-Thalassemia

In homozygous β-thalassemia blood transfusions and chelating therapy cannot prevent completely hemochromatosis. Labile ‘free’ iron forms in blood serum and evolves into insoluble inorganic deposits in tissues. Using X-band EPR at 163 K, we detected a new species of polynuclear iron in serum of some thalassemic patients. It showed a broad g < 2 line and an unusually high dynamic magnetic susceptibility due to ordered magnetism, which was detected by a decreased Q factor of the resonant cavity at B = 0. To explain the ordered magnetism and large line, we postulated either ferri- or ferromagnetic nanocrystals with non-zero residual magnetization, or superparamagnetic nanoparticles with antiferromagnetic ordering and incomplete spin compensation—or maybe both. While the results were not sufficient to check the first hypothesis, they are fully consistent with the second. The new species is similar to, but distinct from, ferritin’s mineral core, as it does not correlate with the ferritin concentration. The spectra suggest particles of ~1.7–4.1 nm diameter, plausibly containing ~40–300 Fe(III) ions coupled by oxygen bridges, but further confirmation is needed. The nanoparticles apparently formed a hydrophilic colloidal dispersion, being probably decorated with hydrophilic small organic molecules. They are postulated to form by heterogeneous nucleation around the ‘free’ iron, then aggregate in chains and eventually precipitate in the tissues. Stable free radicals detected in serum were tentatively identified as the hydroxyperoxyl and monodehydroascorbate radicals forming adducts with Cu(II)-ceruloplasmin, and the Hb–porphyrin–Fe(IV)=O oxoferryl radical probably stabilized on haptoglobin. They are consistent with oxy-radicals promoted both by ‘free’ iron and by polyiron nanoparticles. Potential medical applications like early assessment of patient’s evolution trend toward hemochromatosis and monitoring of the transfusional suppression of endogenous erythrocyte synthesis are suggested.     

Assessment of the systemic distribution of a bioconjugated anti-Her2 magnetic nanoparticle in a breast cancer model by means of magnetic resonance imaging

The aim of this study was to determine the systemic distribution of magnetic nanoparticles of 100 nm diameter (MNPs) coupled to a specific monoclonal antibody anti-Her2 in an experimental breast cancer (BC) model. The study was performed in two groups of Sprague–Dawley rats: control (n = 6) and BC chemically induced (n = 3). Bioconjugated “anti-Her2-MNPs” were intravenously administered, and magnetic resonance imaging (MRI) monitored its systemic distribution at seven times after administration. Non-heme iron presence associated with the location of the bioconjugated anti-Her2-MNPs in splenic, hepatic, cardiac and tumor tissues was detected by Perl’s Prussian blue (PPB) stain. Optical density measurements were used to semiquantitatively determine the iron presence in tissues on the basis of a grayscale values integration of T1 and T2 MRI sequence images. The results indicated a delayed systemic distribution of MNPs in cancer compared to healthy conditions with a maximum concentration of MNPs in cancer tissue at 24 h post-infusion.