Effect of nanoparticle and aggregate size on the relaxometric properties of MR contrast agents based on high quality magnetite nanoparticles

High-performance magnetic artificial silk fibers produced by a scalable and eco-friendly production method

Flexible magnetic materials have great potential for biomedical and soft robotics applications, but they need to be mechanically robust. An extraordinary material from a mechanical point of view is spider silk. Recently, methods for producing artificial spider silk fibers in a scalable and all-aqueous-based process have been developed. If endowed with magnetic properties, such biomimetic artificial spider silk fibers would be excellent candidates for making magnetic actuators. In this study, we introduce magnetic artificial spider silk fibers, comprising magnetite nanoparticles coated with meso-2,3-dimercaptosuccinic acid. The composite fibers can be produced in large quantities, employing an environmentally friendly wet-spinning process. The nanoparticles were found to be uniformly dispersed in the protein matrix even at high concentrations (up to 20% w/w magnetite), and the fibers were superparamagnetic at room temperature. This enabled external magnetic field control of fiber movement, rendering the material suitable for actuation applications. Notably, the fibers exhibited superior mechanical properties and actuation stresses compared to conventional fiber-based magnetic actuators. Moreover, the fibers developed herein could be used to create macroscopic systems with self-recovery shapes, underscoring their potential in soft robotics applications.

Supplementary information

The online version contains supplementary material available at 10.1007/s42114-024-00962-y.

Magnetoliposomes with Calcium-Doped Magnesium Ferrites Anchored in the Lipid Surface for Enhanced DOX Release

Nanotechnology has provided a new insight into cancer treatment by enabling the development of nanocarriers for the encapsulation, transport, and controlled release of antitumor drugs at the target site. Among these nanocarriers, magnetic nanosystems have gained prominence. This work presents the design, development, and characterization of magnetoliposomes (MLs), wherein superparamagnetic nanoparticles are coupled to the lipid surface. For this purpose, dimercaptosuccinic acid (DMSA)-functionalized Ca0.25Mg0.75Fe2O4 superparamagnetic nanoparticles were prepared for the first time. The magnetic nanoparticles demonstrated a cubic shape with an average size of 13.36 nm. Furthermore, their potential for photothermal hyperthermia was evaluated using 4 mg/mL, 2 mg/mL, and 1 mg/mL concentrations of NPs@DMSA, which demonstrated a maximum temperature variation of 20.4 °C, 11.4 °C, and 7.3 °C, respectively, during a 30 min NIR-laser irradiation. Subsequently, these nanoparticles were coupled to the lipid surface of DPPC/DSPC/CHEMS and DPPC/DSPC/CHEMS/DSPE-PEG-based MLs using a new synthesis methodology, exhibiting average sizes of 153 ± 8 nm and 136 ± 2 nm, respectively. Doxorubicin (DOX) was encapsulated with high efficiency, achieving 96% ± 2% encapsulation in non-PEGylated MLs and 98.0% ± 0.6% in stealth MLs. Finally, drug release assays of the DOX-loaded DPPC/DSPC/CHEMS MLs were performed under different conditions of temperature (37 °C and 42 °C) and pH (5.5 and 7.4), simulating physiological and therapeutic conditions. The results revealed a higher release rate at 42 °C and acidic pH. Release rates significantly increased when introducing the stimulus of laser-induced photothermal hyperthermia at 808 nm (1 W/cm2) for 5 min. After 48 h of testing, at pH 5.5, 67.5% ± 0.5% of DOX was released, while at pH 7.4, only a modest release of 27.0% ± 0.1% was achieved. The results demonstrate the potential of the MLs developed in this work to the controlled release of DOX under NIR-laser stimulation and acidic environments and to maintain a sustained and reduced release profile in physiological environments with pH 7.4.

3,4-Dihydroxiphenylacetic Acid-Based Universal Coating Technique for Magnetic Nanoparticles Stabilization for Biomedical Applications

Magnetic nanoparticles based on iron oxide attract researchers' attention due to a wide range of possible applications in biomedicine. As synthesized, most of the magnetic nanoparticles do not form the stable colloidal solutions that are required for the evaluation of their interactions with cells or their efficacy on animal models. For further application in biomedicine, magnetic nanoparticles must be further modified with biocompatible coating. Both the size and shape of magnetic nanoparticles and the chemical composition of the coating have an effect on magnetic nanoparticles' interactions with living objects. Thus, a universal method for magnetic nanoparticles' stabilization in water solutions is needed, regardless of how magnetic nanoparticles were initially synthesized. In this paper, we propose the versatile and highly reproducible ligand exchange technique of coating with 3,4-dihydroxiphenylacetic acid (DOPAC), based on the formation of Fe-O bonds with hydroxyl groups of DOPAC leading to the hydrophilization of the magnetic nanoparticles' surfaces following phase transfer from organic solutions to water. The proposed technique allows for obtaining stable water-colloidal solutions of magnetic nanoparticles with sizes from 21 to 307 nm synthesized by thermal decomposition or coprecipitation techniques. Those stabilized by DOPAC nanoparticles were shown to be efficient in the magnetomechanical actuation of DNA duplexes, drug delivery of doxorubicin to cancer cells, and targeted delivery by conjugation with antibodies. Moreover, the diversity of possible biomedical applications of the resulting nanoparticles was presented. This finding is important in terms of nanoparticle design for various biomedical applications and will reduce nanomedicines manufacturing time, along with difficulties related to comparative studies of magnetic nanoparticles with different magnetic core characteristics.

Selective anisotropic growth of Bi2S3 nanoparticles with adjustable optical properties

We report on the controlled synthesis and functionalization in two steps of elongated Bi₂S₃ nanoparticles within a wide range of sizes. First, we show the effect of the temperature and reaction time on the synthesis of two series of nanoparticles by the reaction of thioacetamide with bismuth(III) neodecanoate in the presence of organic surfactants. At 105 °C and long reaction times, nanoneedles of about 45 nm in length containing larger crystallites are obtained, while highly crystalline nanorods of about 30 nm in length are dominant at 165 °C, regardless of the reaction time. The optical properties of both types of nanoparticles show an enhancement of the band gap compared to bulk Bi₂S₃. This is likely to arise from quantum confinement effects caused by the small particle dimensions relative to the typical exciton size, together with an increase in near-infrared absorption due to the anisotropic particle shape. Second, a ligand exchange approach has been developed to transfer the Bi₂S₃ nanoparticles to aqueous solutions by grafting dimercaptosuccinic acid onto the surface of the particles. The as-prepared coated nanoparticles show good stability in water, in a wide biological pH range, and in phosphate-buffered saline solutions. Overall, this work highlights the controlled design at all levels - from the inorganic core to the organic surface coating - of elongated Bi₂S₃ nanoparticles, leading to a tunable optical response by tuning their morphology and size.

Iron oxide and iron oxyhydroxide nanoparticles impair SARS-CoV-2 infection of cultured cells

Background

Coronaviruses usually cause mild respiratory disease in humans but as seen recently, some human coronaviruses can cause more severe diseases, such as the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the global spread of which has resulted in the ongoing coronavirus pandemic.

Results

In this study we analyzed the potential of using iron oxide nanoparticles (IONPs) coated with biocompatible molecules like dimercaptosuccinic acid (DMSA), 3-aminopropyl triethoxysilane (APS) or carboxydextran (FeraSpin™ R), as well as iron oxyhydroxide nanoparticles (IOHNPs) coated with sucrose (Venofer^®), or iron salts (ferric ammonium citrate -FAC), to treat and/or prevent SARS-CoV-2 infection. At non-cytotoxic doses, IONPs and IOHNPs impaired virus replication and transcription, and the production of infectious viruses in vitro, either when the cells were treated prior to or after infection, although with different efficiencies. Moreover, our data suggest that SARS-CoV-2 infection affects the expression of genes involved in cellular iron metabolism. Furthermore, the treatment of cells with IONPs and IOHNPs affects oxidative stress and iron metabolism to different extents, likely influencing virus replication and production. Interestingly, some of the nanoparticles used in this work have already been approved for their use in humans as anti-anemic treatments, such as the IOHNP Venofer^®, and as contrast agents for magnetic resonance imaging in small animals like mice, such as the FeraSpin™ R IONP.

Conclusions

Therefore, our results suggest that IONPs and IOHNPs may be repurposed to be used as prophylactic or therapeutic treatments in order to combat SARS-CoV-2 infection.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01542-2.

Small-angle X-ray scattering to quantify the incorporation and analyze the disposition of magnetic nanoparticles inside cells

Access to detailed information on cells loaded with nanoparticles with nanoscale precision is of a long-standing interest in many areas of nanomedicine. In this context, designing a single experiment able to provide statistical mean data from a large number of living unsectioned cells concerning information on the nanoparticle size and aggregation inside cell endosomes and accurate nanoparticle cell up-take is of paramount importance. Small-angle X-ray scattering (SAXS) is presented here as a tool to achieve such relevant data. Experiments were carried out in cultures of B16F0 murine melanoma and A549 human lung adenocarcinoma cell lines loaded with various iron oxide nanostructures displaying distinctive structural characteristics. Five systems of water-dispersible magnetic nanoparticles (MNP) of different size, polydispersity and morphology were analyzed, namely, nearly monodisperse MNP with 11 and 13 nm mean size coated with meso-2,3-dimercaptosuccinic acid, more polydisperse 6 nm colloids coated with citric acid and two nanoflowers (NF) systems of 24 and 27 nm in size resulting from the aggregation of 8 nm MNP. Up-take was determined for each system using B16F0 cells. Here we show that SAXS pattern provides high resolution information on nanoparticles disposition inside endosomes of the cytoplasm through the structure factor analysis, on nanoparticles size and dispersity after their incorporation by the cell and on up-take quantification from the extrapolation of the intensity in absolute scale to null scattering vector. We also report on the cell culture preparation to reach sensitivity for the observation of MNP inside cell endosomes using high brightness SAXS synchrotron source. Our results show that SAXS can become a valuable tool for analyzing MNP in cells and tissues.

Effect of different molecular coatings on the heating properties of maghemite nanoparticles

In this work, the effect of different molecular coatings on the alternating magnetic field-induced heating properties of 15 nm maghemite nanoparticles (NPs) in water dispersions was studied at different frequencies (159-782 kHz) and field amplitudes (100-400 G). The original hydrophobic oleate coating was replaced with dimercaptosuccinic acid (DMSA) or polyethylene glycol trimethoxysilane (PEGTMS), while cetrimonium bromide (CTAB) or stearic acid-poloxamer 188 (SA-P188) was intercalated or encapsulated, respectively, to transfer the dispersions into water. Surface modification, based on intercalation processes, induced clustering phenomena with the formation of spherical-like assemblies (CTAB and SA-P188), while ligand-exchange strategies kept the particles isolated. The clustering phenomenon has detrimental effects on the heating performances compared with isolated systems, in line with the reduction of Brown relaxation times. Furthermore, broader comprehension of the heating phenomenon in this dynamic system is obtained by following the evolution of SPA and ILP with time and temperature beyond the initial stage.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Magnetic-Field Directed Vapor-Phase Assembly of Low Fractal Dimension Metal Nanostructures: Experiment and Theory

While gas-phase synthesis techniques offer a scalable approach to production of metal nanoparticles, directed assembly is challenging due to fast particle diffusion rates that lead to random Brownian aggregation. This work explores an electromagnetic-levitation technique to generate metal nanoparticle aggregates with fractal dimension (D_f) below that of diffusion limited assembly. We demonstrate that in addition to levitation and induction heating, the external magnetic field is sufficient to compete with random Brownian forces, which enables the formation of altered fractals. Ferromagnetic metals (Fe, Ni) form chain-like aggregates, while paramagnetic Cu forms compact nanoparticle aggregates with higher D_f values. We have also employed a Monte Carlo simulation to evaluate the necessary field strength to form linear chains in the gas phase.

Engineering Iron Oxide Nanocatalysts by a Microwave-Assisted Polyol Method for the Magnetically Induced Degradation of Organic Pollutants

Advanced oxidation processes constitute a promising alternative for the treatment of wastewater containing organic pollutants. Still, the lack of cost-effective processes has hampered the widespread use of these methodologies. Iron oxide magnetic nanoparticles stand as a great alternative since they can be engineered by different reproducible and scalable methods. The present study consists of the synthesis of single-core and multicore magnetic iron oxide nanoparticles by the microwave-assisted polyol method and their use as self-heating catalysts for the degradation of an anionic (acid orange 8) and a cationic dye (methylene blue). Decolorization of these dyes was successfully improved by subjecting the catalyst to an alternating magnetic field (AMF, 16 kA/m, 200 kHz). The sudden temperature increase at the surface of the catalyst led to an intensification of 10% in the decolorization yields using 1 g/L of catalyst, 0.3 M H₂O₂ and 500 ppm of dye. Full decolorization was achieved at 90 °C, but iron leaching (40 ppm) was detected at this temperature leading to a homogeneous Fenton process. Multicore nanoparticles showed higher degradation rates and 100% efficiencies in four reusability cycles under the AMF. The improvement of this process with AMF is a step forward into more sustainable remediation techniques.

Mono-dispersed nano-hydroxyapatite based MRI probe with tetrahedral DNA nanostructures modification for in vitro tumor cell imaging

Taking advantage of the superior biocompatibility, good stability in a wide pH and temperature range, as well as its strong affinity with DNA of hydroxyapatite (HAp), tetrahedral DNA nanostructures (TDNs) conjugated with AS1411 aptamer (anti-nucleolin overexpressed on tumor cell membranes) were employed as affinity ligands to construct a novel mono-dispersed HAp based probe with Gd³⁺ doping (Apt-TDNs-GdHAp) for MR imaging. The adsorption of TDNs on the nano-HAp surface facilely accomplished the construction of the Apt-TDNs-GdHAp probes. Meanwhile, the use of hydrophilic TDNs not only favored the phase-transfer from the oil phase to the aqueous phase, but also enhanced the mono-dispersion of this probe due to the well-ordered distribution of TDNs on the surface of nano-HAp. Moreover, Apt-TDNs-GdHAp probe with a better mono-dispersion and crystalinity achieved twice higher longitudinal relaxivity (r₁ value) than that of GdHAp synthesized by microwave-assisted method (Microwave-GdHAp), exhibiting much more excellent T₁-weighted imaging performance. With the introduction of TDNs, the stability and the tumor-targeting accessibility were also greatly improved, showing its great potential for further bio-applications.

Continuous growth phenomenon for direct synthesis of monodisperse water-soluble iron oxide nanoparticles with extraordinarily high relaxivity

The direct synthesis of highly water-soluble nanoparticles has attracted intensive interest, but systematic size control has not been reported. Here, we developed a general method for synthesizing monodisperse water-soluble iron oxide nanoparticles with nanometer-scale size increments from 4 nm to 13 nm in a single reaction. Precise size control was achieved by continuous growth in an amphiphilic solvent, diethylene glycol (DEG), where the growth step was separated from the nucleation step by sequential addition of a reactant. There was only one reactant in the synthesis and no need for additional capping agents and reducing agents. This study reveals the "living growth" character of iron oxide nanoparticles synthesised in an amphiphilic solvent. The synthetic method shows high reproducibility. The as-prepared iron oxide nanoparticles are extremely water soluble without any surface modification. Surprisingly, the synthesized 9 nm iron oxide nanoparticles exhibit extremely high transversal and longitudinal relaxivities of 425 mM-1 s-1 and 32 mM-1 s-1 respectively, which is among the highest transversal relaxivity in the literature for sub-10 nm spherical nanoparticles. This study will not only shed light on the continuous growth phenomenon of iron oxide nanoparticles in an amphiphilic solvent, but could also stimulate the synthesis and application of iron oxide nanoparticles. The continuous growth method could be further extended to other materials for the controlled synthesis of water-soluble nanoparticles.

Combined Magnetoliposome Formation and Drug Loading in One Step for Efficient Alternating Current-Magnetic Field Remote-Controlled Drug Release

We have developed a reproducible and facile one step strategy for the synthesis of doxorubicin loaded magnetoliposomes by using a thin-layer evaporation method. Liposomes of around 200 nm were made of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and iron oxide nanoparticles (NPs) with negative, positive, and hydrophobic surfaces that were incorporated outside, inside, or between the lipid bilayers, respectively. To characterize how NPs are incorporated in liposomes, advanced cryoTEM and atomic force microscope (AFM) techniques have been used. It was observed that only when the NPs are attached outside the liposomes, the membrane integrity is preserved (lipid melt transition shifts to 38.7 °C with high enthalpy 34.8 J/g) avoiding the leakage of the encapsulated drug while having good colloidal properties and the best heating efficiency under an alternating magnetic field (AMF). These magnetoliposomes were tested with two cancer cell lines, MDA-MB-231 and HeLa cells. First, 100% of cellular uptake was achieved with a high cell survival (above 80%), which is preserved (83%) for doxorubicin-loaded magnetoliposomes. Then, we demonstrate that doxorubicin release can be triggered by remote control, using a noninvasive external AMF for 1 h, leading to a cell survival reduction of 20%. Magnetic field conditions of 202 kHz and 30 mT seem to be enough to produce an effective heating to avoid drug degradation. In conclusion, these drug-loaded magnetoliposomes prepared in one step could be used for drug release on demand at a specific time and place, efficiently using an external AMF to reduce or even eliminate side effects.

MRI Detectable Polymer Microspheres Embedded With Magnetic Ferrite Nanoclusters For Embolization: In Vitro And In Vivo Evaluation

OBJECTIVE

The objective of this study was to develop magnetic embolic microspheres that could be visualized by clinical magnetic resonance imaging (MRI) scanners aiming to improve the efficiency and safety of embolotherapy.

METHODS AND DISCUSSION

Magnetic ferrite nanoclusters (FNs) were synthesized with microwave-assisted solvothermal method, and their morphology, particle size, crystalline structure, magnetic properties as well as T2 relaxivity were characterized to confirm the feasibility of FNs as an MRI probe. Magnetic polymer microspheres (FNMs) were then produced by inverse suspension polymerization with FNs embedded inside. The physicochemical and mechanical properties (including morphology, particle size, infrared spectra, elasticity, etc.) of FNMs were investigated, and the magnetic properties and MRI detectable properties of FNMs were also assayed by vibrating sample magnetometer and MRI scanners. Favorable biocompatibility and long-term MRI detectability of FNMs were then studied in mice by subcutaneous injection. FNMs were further used to embolize rabbits' kidneys to evaluate the embolic property and detectability by MRI.

CONCLUSION

FNMs could serve as a promising MRI-visualized embolic material for embolotherapy in the future.

Magnetic Nanoclusters Coated with Albumin, Casein, and Gelatin: Size Tuning, Relaxivity, Stability, Protein Corona, and Application in Nuclear Magnetic Resonance Immunoassay

The surface functionalization of magnetic nanoparticles improves their physicochemical properties and applicability in biomedicine. Natural polymers, including proteins, are prospective coatings capable of increasing the stability, biocompatibility, and transverse relaxivity (r2) of magnetic nanoparticles. In this work, we functionalized the nanoclusters of carbon-coated iron nanoparticles with four proteins: bovine serum albumin, casein, and gelatins A and B, and we conducted a comprehensive comparative study of their properties essential to applications in biosensing. First, we examined the influence of environmental parameters on the size of prepared nanoclusters and synthesized protein-coated nanoclusters with a tunable size. Second, we showed that protein coating does not significantly influence the r2 relaxivity of clustered nanoparticles; however, the uniform distribution of individual nanoparticles inside the protein coating facilitates increased relaxivity. Third, we demonstrated the applicability of the obtained nanoclusters in biosensing by the development of a nuclear-magnetic-resonance-based immunoassay for the quantification of antibodies against tetanus toxoid. Fourth, the protein coronas of nanoclusters were studied using SDS-PAGE and Bradford protein assay. Finally, we compared the colloidal stability at various pH values and ionic strengths and in relevant complex media (i.e., blood serum, plasma, milk, juice, beer, and red wine), as well as the heat stability, resistance to proteolytic digestion, and shelf-life of protein-coated nanoclusters.

Understanding the Influence of a Bifunctional Polyethylene Glycol Derivative in Protein Corona Formation around Iron Oxide Nanoparticles

Superparamagnetic iron oxide nanoparticles are one of the most prominent agents used in theranostic applications, with MRI imaging the main application assessed. The biomolecular interface formed on the surface of a nanoparticle in a biological medium determines its behaviour in vitro and in vivo. In this study, we have compared the formation of the protein corona on highly monodisperse iron oxide nanoparticles with two different coatings, dimercaptosuccinic acid (DMSA), and after conjugation, with a bifunctional polyethylene glycol (PEG)-derived molecule (2000 Da) in the presence of Wistar rat plasma. The protein fingerprints around the nanoparticles were analysed in an extensive proteomic study. The results presented in this work indicate that the composition of the protein corona is very difficult to predict. Proteins from different functional categories—cell components, lipoproteins, complement, coagulation, immunoglobulins, enzymes and transport proteins—were identified in all samples with very small variability. Although both types of nanoparticles have similar amounts of bonded proteins, very slight differences in the composition of the corona might explain the variation observed in the uptake and biotransformation of these nanoparticles in Caco-2 and RAW 264.7 cells. Cytotoxicity was also studied using a standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Controlling nanoparticles’ reactivity to the biological environment by deciding on its surface functionalization may suggest new routes in the control of the biodistribution, biodegradation and clearance of multifunctional nanomedicines.

Nanoparticles for Biomedicine: Coagulation During Synthesis and Applications

Nanoparticle-based systems offer fascinating possibilities for biomedicine, but their translation into clinics is slow. Missing sterile, reproducible, and scalable methods for their synthesis along with challenges in characterization and poor colloidal stability of nanoparticles in body fluids are key obstacles. Flame aerosol technology gives proven access to scalable synthesis of nanoparticles with diverse compositions and architectures. Although highly promising in terms of product reproducibility and sterility, this technology is frequently overlooked, as its products are of fractal-like aggregated and/or agglomerated morphology. However, coagulation is a widely occurring phenomenon in all kinds of particle-based systems. In particular, protein-rich body fluids encountered in biomedical settings often lead to destabilization of colloidal nanoparticle suspensions in vivo. We aim to provide insights into how particle–particle interactions can be measured and controlled. Moreover, we show how particle coupling effects driven by coagulation may even be beneficial for certain sensing, therapeutic, and bioimaging applications.

Agglomeration of 10 nm amine-functionalized nano-magnetite does not hinder its efficiency as an environmental adsorbent

Amine-functionalized magnetite (nFe₃O₄-NH₂) of two different sizes, 10 nm and 250 nm, were compared as environmental adsorbents. They were synthesized by co-precipitation (10 nm-nFe₃O₄-NH₂) and solvothermal (250 nm-nFe₃O₄-NH₂) methods, respectively. The prepared amine-functionalized magnetite was characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectroscopy, size distribution analysis and surface area analysis to compare the properties of different sizes of nFe₃O₄-NH₂. Both nFe₃O₄-NH₂ contained cubic Fe₃O₄ crystalline structure. The 250 nm-nFe₃O₄-NH₂ exhibited higher magnetic saturation value than the 10 nm-nFe₃O₄-NH₂, but both could be separated from an aqueous solution using an external magnet. The surface area and pore volume of the smaller-sized 10 nm-nFe₃O₄-NH₂ was larger than that of 250 nm-nFe₃O₄-NH₂, but stronger aggregation was observed in the 10 nm-nFe₃O₄-NH₂. Batch adsorption of lead indicated that the 10 nm-nFe₃O₄-NH₂ was a better adsorbent than the 250 nm-nFe₃O₄-NH₂. The maximum adsorption capacity of lead for the 10 nm-nFe₃O₄-NH₂ and the 250 nm-nFe₃O₄-NH₂ were 74.48 mg g^-1 and 54.54 mg g^-1, respectively. The stronger aggregation of nanoparticles with a smaller particle size did not affect the superior performance of the 10 nm-nFe₃O₄-NH₂ as an environmental adsorbent.

Improving the reliability of the iron concentration quantification for iron oxide nanoparticle suspensions: a two-institutions study

Most iron oxide nanoparticles applications, and in special biomedical applications, require the accurate determination of iron content as the determination of particle properties from measurements in dispersions is strongly dependent on it. Inductively coupled plasma (ICP) and spectrophotometry are two typical worldwide used analytical methods for iron concentration determination. In both techniques, precise determination of iron is not straightforward and nanoparticle digestion and dilution procedures are needed prior to analysis. The sample preparation protocol has been shown to be as important as the analytical method when accuracy is aimed as many puzzling reported results in magnetic, colloidal, and structural properties are simply attributable to inadequate dissolution procedures. Therefore, a standard sample preparation protocol is needed to ensure the adequate and complete iron oxide nanoparticle dissolution and to harmonize this procedure. In this work, an interlaboratory evaluation of an optimized iron oxide nanoparticle digestion/dilution protocol was carried out. The presented protocol is simple, inexpensive, and does not involve any special device (as microwave, ultrasound, or other high-priced digestion devices). Then, iron concentration was measured by ICP-OES (performed in ICMM/CSIC-Spain) and spectrophotometry (NanoPET-Germany) and the obtained concentration values were analyzed to determine the most probable error causes. Uncertainty values as low as 1.5% were achieved after the optimized method was applied. Moreover, this article provides a list of recommendations to significantly reduce uncertainty in both sample preparation and analysis procedures.

VSION as high field MRI T1 contrast agent: evidence of their potential as positive contrast agent for magnetic resonance angiography

Because of their outstanding magnetic properties, iron oxide nanoparticles have already been the subject of numerous studies in the biomedical field, in particular as a negative contrast agent for T₂-weighted nuclear magnetic resonance imaging, or as therapeutic agents in hyperthermia experiments. Recent studies have shown that below a given particle size (i.e. 5 nm), iron oxide may be used to provide a significant positive (brightening) effect on T₁-weighted MRI. In such an application, not only the size of the crystal, but also the control of the coating process is essential to ensure optimal properties, especially at a very high field (> 3 T). In this work, we focused on the development of very small iron oxide nanoparticles as a potential platform for high field T₁ magnetic resonance angiography (MRA) applications. The feasibility has been evaluated in vivo at 9.4 T, demonstrating the usefulness of the developed system for MRA applications.

On the use of superparamagnetic hydroxyapatite nanoparticles as an agent for magnetic and nuclear in vivo imaging

The identification of alternative biocompatible magnetic NPs for advanced clinical application is becoming an important need due to raising concerns about iron accumulation in soft issues associated to the administration of superparamagnetic iron oxide nanoparticles (NPs). Here, we report on the performance of previously synthetized iron-doped hydroxyapatite (FeHA) NPs as contrast agent for magnetic resonance imaging (MRI). The MRI contrast abilities of FeHA and Endorem® (dextran coated iron oxide NPs) were assessed by ¹H nuclear magnetic resonance relaxometry and their performance in healthy mice was monitored by a 7 Tesla scanner. FeHA applied a higher contrast enhancement, and had a longer endurance in the liver with respect to Endorem® at iron equality. Additionally, a proof of concept of FeHA use as scintigraphy imaging agent for positron emission tomography (PET) and single photon emission computed tomography (SPECT) was given labeling FeHA with ^99mTc-MDP by a straightforward surface functionalization process. Scintigraphy/x-ray fused imaging and ex vivo studies confirmed its dominant accumulation in the liver, and secondarily in other organs of the mononuclear phagocyte system. FeHA efficiency as MRI-T₂ and PET-SPECT imaging agent combined to its already reported intrinsic biocompatibility qualifies it as a promising material for innovative nanomedical applications.

STATEMENT OF SIGNIFICANCE

The ability of iron-doped hydroxyapatite nanoaprticles (FeHA) to work in vivo as imaging agents for magnetic resonance (MR) and nuclear imaging is demonstrated. FeHA applied an higher MR contrast in the liver, spleen and kidneys of mice with respect to Endorem®. The successful radiolabeling of FeHA allowed for scintigraphy/X-ray and ex vivo biodistribution studies, confirming MR results and envisioning FeHA application for dual-imaging.

Key Parameters on the Microwave Assisted Synthesis of Magnetic Nanoparticles for MRI Contrast Agents

Uniform iron oxide magnetic nanoparticles have been synthesized using a microwave assisted synthesis method in organic media and their colloidal, magnetic, and relaxometric properties have been analyzed after its transference to water and compared with those nanoparticles prepared by thermal decomposition in organic media. The novelty of this synthesis relies on the use of a solid iron oleate as precursor, which assures the reproducibility and scalability of the synthesis, and the microwave heating that resulted in being faster and more efficient than traditional heating methods, and therefore it has a great potential for nanoparticle industrial production. The effect of different experimental conditions such as the solvent, precursor, and surfactant concentration and reaction time as well as the transference to water is analyzed and optimized to obtain magnetic iron oxide nanoparticles with sizes between 8 and 15 nm and finally colloids suitable for their use as contrast agents on Magnetic Resonance Imaging (MRI). The r₂ relaxivity values normalized to the square of the saturation magnetization were shown to be constant and independent of the particle size, which means that the saturation magnetization is the main parameter controlling the efficiency of these magnetic nanoparticles as MRI T₂-contrast agents.

Multimodality Imaging of Angiogenesis in a Rabbit Atherosclerotic Model by GEBP11 Peptide Targeted Nanoparticles

Background and Aims: Angiogenesis is an important pathological process during progression of plaque formation, which can result in plaque hemorrhage and vulnerability. This study aims to explore non-invasive imaging of angiogenesis in atherosclerotic plaque through magnetic resonance imaging (MRI) and positron emission tomography (PET) by using GEBP11 peptide targeted magnetic iron oxide nanoparticles in a rabbit model of atherosclerosis.

Methods: The dual-modality imaging probe was constructed by coupling 2, 3-dimercaptosuccinnic acid-coated paramagnetic nanoparticles (DMSA-MNPs) and the PET ⁶⁸Ga chelator 1,4,7-triazacyclononane-N, N', N''-triacetic acid (NOTA) to GEBP11 peptide. The atherosclerosis model was induced in New Zealand white rabbits by abdominal aorta balloon de-endothelialization and atherogenic diet for 12 weeks. The plaque areas in abdominal artery were detected by ultrasound imaging and Oil Red O staining. Immunofluorescence staining and Prussian blue staining were applied respectively to investigate the affinity of GEBP11 peptide. MTT and flow cytometric analysis were performed to detect the effects of NGD-MNPs on cell proliferation, cell cycle and apoptosis in Human umbilical vein endothelial cells (HUVECs). In vivo MRI and PET imaging of atherosclerotic plaque were carried out at different time points after intravenous injection of nanoparticles.

Results: The NGD-MNPs with hydrodynamic diameter of 130.8 nm ± 7.1 nm exhibited good imaging properties, high stability, low immunogenicity and little cytotoxicity. In vivo PET/MR imaging revealed that ⁶⁸Ga-NGD-MNPs were successfully applied to visualize atherosclerotic plaque angiogenesis in the rabbit abdominal aorta. Prussian blue and CD31 immunohistochemical staining confirmed that NGD-MNPs were well co-localized within the blood vessels' plaques.

Conclusion:⁶⁸Ga-NGD-MNPs might be a promising MR and PET dual imaging probe for visualizing the vulnerable plaques.

Assembly of Iron Oxide Nanocubes for Enhanced Cancer Hyperthermia and Magnetic Resonance Imaging

Multiple formulations of iron oxide nanoparticles (IONPs) have been proposed for enhancing contrast in magnetic resonance imaging (MRI) and for increasing efficacy in thermal ablation therapies. However, insufficient accumulation at the disease site and low magnetic performance hamper the clinical application of IONPs. Here, 20 nm iron oxide nanocubes were assembled into larger nanoconstructs externally stabilized by a serum albumin coating. The resulting assemblies of nanocubes (ANCs) had an average diameter of 100 nm and exhibited transverse relaxivity (r₂ = 678.9 ± 29.0 mM^‒1·s^‒1 at 1.41 T) and heating efficiency (specific absorption rate of 109.8 ± 12.8 W·g^‒1 at 512 kHz and 10 kA·m^‒1). In mice bearing glioblastoma multiforme tumors, Cy5.5-labeled ANCs allowed visualization of malignant masses via both near infrared fluorescent and magnetic resonance imaging. Also, upon systemic administration of ANCs (5 mg_Fe·kg^‒1), 30 min of daily exposure to alternating magnetic fields for three consecutive days was sufficient to halt tumor progression. This study demonstrates that intravascular administration of ANCs can effectively visualize and treat neoplastic masses.

SAXS analysis of single- and multi-core iron oxide magnetic nanoparticles

Comprehensive characterization of the morphology of single-core and multi-core magnetic nanoparticle systems for future use as reference materials for magnetic properties was performed using a combination of small-angle X-ray scattering and static light scattering. The composition of the nanoparticle iron oxide cores was determined using XANES.

This article reports on the characterization of four superparamagnetic iron oxide nanoparticles stabilized with dimercaptosuccinic acid, which are suitable candidates for reference materials for magnetic properties. Particles p₁ and p₂ are single-core particles, while p₃ and p₄ are multi-core particles. Small-angle X-ray scattering analysis reveals a lognormal type of size distribution for the iron oxide cores of the particles. Their mean radii are 6.9 nm (p₁), 10.6 nm (p₂), 5.5 nm (p₃) and 4.1 nm (p₄), with narrow relative distribution widths of 0.08, 0.13, 0.08 and 0.12. The cores are arranged as a clustered network in the form of dense mass fractals with a fractal dimension of 2.9 in the multi-core particles p₃ and p₄, but the cores are well separated from each other by a protecting organic shell. The radii of gyration of the mass fractals are 48 and 44 nm, and each network contains 117 and 186 primary particles, respectively. The radius distributions of the primary particle were confirmed with transmission electron microscopy. All particles contain purely maghemite, as shown by X-ray absorption fine structure spectroscopy.

A novel approach to analyze lysosomal dysfunctions through subcellular proteomics and lipidomics: the case of NPC1 deficiency

Superparamagnetic iron oxide nanoparticles (SPIONs) have mainly been used as cellular carriers for genes and therapeutic products, while their use in subcellular organelle isolation remains underexploited. We engineered SPIONs targeting distinct subcellular compartments. Dimercaptosuccinic acid-coated SPIONs are internalized and accumulate in late endosomes/lysosomes, while aminolipid-SPIONs reside at the plasma membrane. These features allowed us to establish standardized magnetic isolation procedures for these membrane compartments with a yield and purity permitting proteomic and lipidomic profiling. We validated our approach by comparing the biomolecular compositions of lysosomes and plasma membranes isolated from wild-type and Niemann-Pick disease type C1 (NPC1) deficient cells. While the accumulation of cholesterol and glycosphingolipids is seen as a primary hallmark of NPC1 deficiency, our lipidomics analysis revealed the buildup of several species of glycerophospholipids and other storage lipids in selectively late endosomes/lysosomes of NPC1-KO cells. While the plasma membrane proteome remained largely invariable, we observed pronounced alterations in several proteins linked to autophagy and lysosomal catabolism reflecting vesicular transport obstruction and defective lysosomal turnover resulting from NPC1 deficiency. Thus the use of SPIONs provides a major advancement in fingerprinting subcellular compartments, with an increased potential to identify disease-related alterations in their biomolecular compositions.

Superparamagnetic iron oxide nanoparticles functionalized by peptide nucleic acids

Hydrophilic SPION were decorated with PNA decamers by SH/maleimide clickreaction as potential MRI and hyperthermia agents, and PNA carriers.

Quantitative Measurement of Ligand Exchange with Small-Molecule Ligands on Iron Oxide Nanoparticles via Radioanalytical Techniques

Ligand exchange on the surface of hydrophobic iron oxide nanoparticles is a common method for controlling surface chemistry for a desired application. Furthermore, ligand exchange with small-molecule ligands may be necessary to obtain particles with a specific size or functionality. Understanding to what extent ligand exchange occurs and what factors affect it is important for the optimization of this critical procedure. However, quantifying the amount of exchange may be difficult because of the limitations of commonly used characterization techniques. Therefore, we utilized a radiotracer technique to track the exchange of a radiolabeled ¹⁴C-oleic acid ligand with hydrophilic small-molecule ligands on the surface of iron oxide nanoparticles. Iron oxide nanoparticles functionalized with ¹⁴C-oleic acid were modified with small-molecule ligands with terminal functional groups including catechols, phosphonates, sulfonates, thiols, carboxylic acids, and silanes. These moieties were selected because they represent the most commonly used ligands for this procedure. The effectiveness of these molecules was compared using both procedures widely found in the literature and using a standardized procedure. After ligand exchange, the nanoparticles were analyzed using liquid scintillation counting (LSC) and inductively coupled plasma-mass spectrometry. The labeled and unlabeled particles were further characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) to determine the particle size, hydrodynamic diameter, and zeta potential. The unlabeled particles were characterized via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and vibrating sample magnetometry (VSM) to confirm the presence of the small molecules on the particles and verify the magnetic properties, respectively. Radioanalytical determination of ¹⁴C-oleic acid was used to calculate the total amount of oleic acid remaining on the surface of the particles after ligand exchange. The results revealed that the ligand-exchange reactions performed using widely cited procedures did not go to completion. Residual oleic acid remained on the particles after these reactions and the reactions using a standardized protocol. A comparison of the ligand-exchange procedures indicated that the binding moiety, multidenticity, reaction time, temperature, and presence of a catalyst impacted the extent of exchange. Quantification of the oleic acid remaining after ligand exchange revealed a binding hierarchy in which catechol-derived anchor groups displace the most oleic acid on the surface of the nanoparticles and the thiol group displaces the least amount of oleic acid. Thorough characterization of ligand exchange is required to develop nanoparticles suitable for their intended application.

Scalable Synthesis of Ag Networks with Optimized Sub-monolayer Au-Pd Nanoparticle Covering for Highly Enhanced SERS Detection and Catalysis

Highly porous tri-metallic Ag_xAu_yPd_z networks with a sub-monolayer bimetallic Au-Pd nanoparticle coating were synthesized via a designed galvanic replacement reaction of Ag nanosponges suspended in mixed solutions of HAuCl₄ and K₂PdCl₄. The resulting networks’ ligaments have a rough surface with bimetallic nanoparticles and nanopores due to removal of Ag. The surface morphology and composition are adjustable by the temperature and mixed solutions’ concentration. Very low combined Au and Pd atomic percentage (1−x) where x is atomic percentage of Ag leads to sub-monolayer nanoparticle coverings allowing a large number of active boundaries, nanopores, and metal-metal interfaces to be accessible. Optimization of the Au/Pd atomic ratio y/z obtains large surface-enhanced Raman scattering detection sensitivity (at y/z = 5.06) and a higher catalytic activity (at y/z = 3.55) toward reduction reactions as benchmarked with 4-nitrophenol than for most bimetallic catalysts. Subsequent optimization of x (at fixed y/z) further increases the catalytic activity to obtain a superior tri-metallic catalyst, which is mainly attributed to the synergy of several aspects including the large porosity, increased surface roughness, accessible interfaces, and hydrogen absorption capacity of nanosized Pd. This work provides a new concept for scalable synthesis and performance optimization of tri-metallic nanostructures.

Targeting T1 and T2 dual modality enhanced magnetic resonance imaging of tumor vascular endothelial cells based on peptides-conjugated manganese ferrite nanomicelles

Tumor angiogenesis plays very important roles for tumorigenesis, tumor development, metastasis, and prognosis. Targeting T₁/T₂ dual modality magnetic resonance (MR) imaging of the tumor vascular endothelial cells (TVECs) with MR molecular probes can greatly improve diagnostic sensitivity and specificity, as well as helping to make an early diagnosis of tumor at the preclinical stage. In this study, a new T₁ and T₂ dual modality nanoprobe was successfully fabricated. The prepared nanoprobe comprise peptides CL 1555, poly(ε-caprolactone)-block-poly(ethylene glycol) amphiphilic copolymer shell, and dozens of manganese ferrite (MnFe₂O₄) nanoparticle core. The results showed that the hydrophobic MnFe₂O₄ nanoparticles were of uniform spheroidal appearance and narrow size distribution. Due to the self-assembled nanomicelles structure, the prepared probes were of high relaxivity of 281.7 mM⁻¹ s⁻¹, which was much higher than that of MnFe₂O₄ nanoparticles (67.5 mM 1 s⁻¹). After being grafted with the targeted CD105 peptide CL 1555, the nanomicelles can combine TVECs specifically and make the labeled TVECs dark in T₂-weighted MR imaging. With the passage on, the Mn²⁺ ions were released from MnFe₂O₄ and the size decreased gradually, making the signal intensity of the second and third passage of labeled TVECs increased in T₁-weighted MR imaging. Our results demonstrate that CL-poly(ethylene glycol)-MnFe₂O₄ can conjugate TVECs and induce dark and bright contrast in MR imaging, and act as a novel molecular probe for T₁- and T₂-enhanced MR imaging of tumor angiogenesis.

Subsurface imaging of silicon nanowire circuits and iron oxide nanoparticles with sub-10 nm spatial resolution

Non-destructive subsurface characterization of nanoscale structures and devices is of significant interest in nanolithography and nanomanufacturing. In those areas, the accurate location of the buried structures and their nanomechanical properties are relevant for optimization of the nanofabrication process and the functionality of the system. Here we demonstrate the capabilities of bimodal and trimodal force microscopy for imaging silicon nanowire devices buried under an ultrathin polymer film. We resolve the morphology and periodicities of silicon nanowire pairs. We report a spatial resolution in the sub-10 nm range for nanostructures buried under a 70 nm thick polymer film. By using numerical simulations we explain the role of the excited modes in the subsurface imaging process. Independent of the bimodal or trimodal atomic force microscopy approach, the fundamental mode is the most suitable for tracking the topography while the higher modes modulate the interaction of the tip with the buried nanostructures and provide subsurface contrast.

Design of iron oxide-based nanoparticles for MRI and magnetic hyperthermia

Iron oxide nanoparticles are widely used for biological applications thanks to their outstanding balance between magnetic properties, surface-to-volume ratio suitable for efficient functionalization and proven biocompatibility. Their development for MRI or magnetic particle hyperthermia concentrates much of the attention as these nanomaterials are already used within the health system as contrast agents and heating mediators. As such, the constant improvement and development for better and more reliable materials is of key importance. On this basis, this review aims to cover the rational design of iron oxide nanoparticles to be used as MRI contrast agents or heating mediators in magnetic hyperthermia, and reviews the state of the art of their use as nanomedicine tools.

Versatile theranostics agents designed by coating ferrite nanoparticles with biocompatible polymers

Three biocompatible polymers, polyethylene glycol (PEG), dextran and chitosan, have been used in this work to control the colloidal stability of magnetic nanoparticles (14 ± 5 nm in diameter) and to vary the aggregation state in order to study their effect on relaxometric and heating properties. Two different coating strategies have been deeply developed; one based on the formation of an amide bond between citric acid coated nanoparticles (NPs) and amine groups present on the polymer surface and the other based on the NP encapsulation. Relaxometric properties revealed that proton relaxation rates strongly depend on the coating layer hydrophilicity and the aggregation state of the particles due to the presence of magnetic interactions. Thus, while PEG coating reduces particle aggregation by increasing inter-particle spacing leading to reduction of both T1 and T2 relaxation, dextran and chitosan lead to an increase mainly in T2 values due to the aggregation of particles in bigger clusters where they are in close contact. Dextran and chitosan coated NPs have also shown a remarkable heating effect during the application of an alternating magnetic field. They have proved to be potential candidates as theranostic agents for cancer diagnosis and treatment. Finally, cytotoxicity of PEG conjugated NPs, which seem to be ideal for intravenous administration because of their small hydrodynamic size, was investigated resulting in high cell viability even at 0.2 mg Fe ml(-1) after 24 h of incubation. This suspension can be used as drug/biomolecule carrier for in vivo applications.

Increased transverse relaxivity in ultrasmall superparamagnetic iron oxide nanoparticles used as MRI contrast agent for biomedical imaging

Synthesis of a contrast agent for biomedical imaging is of great interest where magnetic nanoparticles are concerned, because of the strong influence of particle size on transverse relaxivity. In the present study, biocompatible magnetic iron oxide nanoparticles were synthesized by co-precipitation of Fe²⁺ and Fe³⁺ salts, followed by surface adsorption with reduced dextran. The synthesized nanoparticles were spherical in shape, and 12 ± 2 nm in size as measured using transmission electron microscopy; this was corroborated with results from X-ray diffraction and dynamic light scattering studies. The nanoparticles exhibited superparamagnetic behavior, superior T₂ relaxation rate and high relaxivities (r₁  = 18.4 ± 0.3, r₂  = 90.5 ± 0.8 s^-1 mM^-1 , at 7 T). MR image analysis of animals before and after magnetic nanoparticle administration revealed that the signal intensity of tumor imaging, specific organ imaging and whole body imaging can be clearly distinguished, due to the strong relaxation properties of these nanoparticles. Very low concentrations (3.0 mg Fe/kg body weight) of iron oxides are sufficient for early detection of tumors, and also have a clear distinction in pre- and post-enhancement of contrast in organs and body imaging. Many investigators have demonstrated high relaxivities of magnetic nanoparticles at superparamagnetic iron oxide level above 50 nm, but this investigation presents a satisfactory, ultrasmall, superparamagnetic and high transverse relaxivity negative contrast agent for diagnosis in pre-clinical studies. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of Nanoclustering and Dipolar Interactions in Heat Generation for Magnetic Hyperthermia

Biomedical magnetic colloids commonly used in magnetic hyperthermia experiments often display a bidisperse structure, i.e., are composed of stable nanoclusters coexisting with well-dispersed nanoparticles. However, the influence of nanoclusters in the optimization of colloids for heat dissipation is usually excluded. In this work, bidisperse colloids are used to analyze the effect of nanoclustering and long-range magnetic dipolar interaction on the magnetic hyperthermia efficiency. Two kinds of colloids, composed of magnetite cores with mean sizes of around 10 and 18 nm, coated with oleic acid and dispersed in hexane, and coated with meso-2,3-dimercaptosuccinic acid and dispersed in water, were analyzed. Small-angle X-ray scattering was applied to thoroughly characterize nanoparticle structuring. We proved that the magnetic hyperthermia performances of nanoclusters and single nanoparticles are distinctive. Nanoclustering acts to reduce the specific heating efficiency whereas a peak against concentration appears for the well-dispersed component. Our experiments show that the heating efficiency of a magnetic colloid can increase or decrease when dipolar interactions increase and that the colloid concentration, i.e., dipolar interaction, can be used to improve magnetic hyperthermia. We have proven that the power dissipated by an ensemble of dispersed magnetic nanoparticles becomes a nonextensive property as a direct consequence of the long-range nature of dipolar interactions. This knowledge is a key point in selecting the correct dose that has to be injected to achieve the desired outcome in intracellular magnetic hyperthermia therapy.

Superparamagnetic Fe3O4 nanoparticles: synthesis by a solvothermal process and functionalization for a magnetic targeted curcumin delivery system

Different functionalized Fe₃O₄ nanoparticles were fabricated for constructing magnetic targeted carriers for curcumin to improve its hydrophilicity and bioavailability.

In vitro and in vivo MRI visualization of nanocomposite biodegradable microcapsules with tunable contrast

Tunable MRI contrast of microcapsules was obtained.

Ultra-large-scale production of ultrasmall superparamagnetic iron oxide nanoparticles for T1-weighted MRI

Ultra-large-scale production of ultrasmall superparamagnetic iron oxide nanoparticles for magnetic resonance angiography.

Exploiting Size-Dependent Drag and Magnetic Forces for Size-Specific Separation of Magnetic Nanoparticles

Realizing the full potential of magnetic nanoparticles (MNPs) in nanomedicine requires the optimization of their physical and chemical properties. Elucidation of the effects of these properties on clinical diagnostic or therapeutic properties, however, requires the synthesis or purification of homogenous samples, which has proved to be difficult. While initial simulations indicated that size-selective separation could be achieved by flowing magnetic nanoparticles through a magnetic field, subsequent in vitro experiments were unable to reproduce the predicted results. Magnetic field-flow fractionation, however, was found to be an effective method for the separation of polydisperse suspensions of iron oxide nanoparticles with diameters greater than 20 nm. While similar methods have been used to separate magnetic nanoparticles before, no previous work has been done with magnetic nanoparticles between 20 and 200 nm. Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis were used to confirm the size of the MNPs. Further development of this work could lead to MNPs with the narrow size distributions necessary for their in vitro and in vivo optimization.

Architectured design of superparamagnetic Fe3O4nanoparticles for application as MRI contrast agents: mastering size and magnetism for enhanced relaxivity

Superparamagnetic Fe₃O₄nanomaterials with enhanced relaxivity were prepared by coprecipitation using different alkanolamine bases, which mastered the materials' surface magnetic properties upon size reduction.

Effects of phase transfer ligands on monodisperse iron oxide magnetic nanoparticles

Oleic acid coated iron oxide nanoparticles synthesized by thermal decomposition in organic medium are highly monodisperse but at the same time are unsuitable for biological applications. Ligand-exchange reactions are useful to make their surface hydrophilic. However, these could alter some structural and magnetic properties of the modified particles. Here we present a comprehensive study and comparison of the effects of employing either citric acid (CA) or meso-2,3-dimercaptosuccinic acid (DMSA) ligand-exchange protocols for phase transfer of monodisperse hydrophobic iron oxide nanoparticles produced by thermal decomposition of Fe(acac)3 in benzyl ether. We show the excellent hydrodynamic size distribution and colloidal stability of the hydrophilic particles obtained by the two protocols and confirm that there is a certain degree of oxidation caused by the ligand-exchange. CA revealed to be more aggressive towards the iron oxide surface than DMSA and greatly reduced the saturation magnetization values and initial susceptibility of the resulting particles compared to the native ones. Besides being milder and more straightforward to perform, the DMSA ligand exchange protocol produces MNP chemically more versatile for further functionalization possibilities. This versatility is shown through the covalent linkage of gum Arabic onto MNP-DMSA using carboxyl and thiol based chemical routes and yielding particles with comparable properties.

Iron oxide nanoparticles stabilized with dendritic polyglycerols as selective MRI contrast agents

Monodisperse small iron oxide nanoparticles functionalized with dendritic polyglycerol (dPG) or dendritic polyglycerol sulfate (dPGS) are prepared. They are highly stable in aqueous solutions as well as physiological media. In particular, oleic acid capped iron oxide particles (core diameter = 11 ± 1 nm) were modified by a ligand exchange process in a one pot synthesis with dPG and dPGS bearing phosphonate as anchor groups. Dynamic light scattering measurements performed in water and different biological media demonstrate that the hydrodynamic diameter of the particles is only slightly increased by the ligand exchange process resulting in a final diameter of less than 30 nm and that the particles are stable in these media. It is also revealed by magnetic resonance studies that their magnetic relaxivity is reduced by the surface modification but it is still sufficient for high contrast magnetic resonance imaging (MRI). Additionally, incubation of dPGS functionalized iron oxide nanoparticles with human umbilical vein endothelial cells showed a 50% survival at 85 nM (concentration of nanoparticles). Surface plasmon resonance (SPR) studies demonstrate that the dPGS functionalized iron oxide nanoparticles inhibit L-selectin ligand binding whereas the particles containing only dPG do not show this effect. Experiments in a flow chamber with human myelogenous leukemia cells confirmed L-selectin inhibition of the dPGS functionalized iron oxide nanoparticles and with that the L-selectin mediated leukocyte adhesion. These results indicate that dPGS functionalized iron oxide nanoparticles are a promising contrast agent for inflamed tissue probed by MRI.

Synthesis of multifunctional magnetic nanoflakes for magnetic resonance imaging, hyperthermia, and targeting

Iron oxide nanoparticles (IOs) are intrinsically theranostic agents that could be used for magnetic resonance imaging (MRI) and local hyperthermia or tissue thermal ablation. Yet, effective hyperthermia and high MR contrast have not been demonstrated within the same nanoparticle configuration. Here, magnetic nanoconstructs are obtained by confining multiple, ∼ 20 nm nanocubes (NCs) within a deoxy-chitosan core. The resulting nanoconstructs-magnetic nanoflakes (MNFs)-exhibit a hydrodynamic diameter of 156 ± 3.6 nm, with a polydispersity index of ∼0.2, and are stable in PBS up to 7 days. Upon exposure to an alternating magnetic field of 512 kHz and 10 kA m(-1), MNFs provide a specific absorption rate (SAR) of ∼75 W gFe(-1), which is 4-15 times larger than that measured for conventional IOs. Moreover, the same nanoconstructs provide a remarkably high transverse relaxivity of ∼500 (mM s)(-1), at 1.41T. MNFs represent a first step toward the realization of nanoconstructs with superior relaxometric and ablation properties for more effective theranostics.

Hierarchically-Structured Magnetic Nanoconstructs with Enhanced Relaxivity and Cooperative Tumor Accumulation

Iron oxide nanoparticles are formidable multifunctional systems capable of contrast enhancement in magnetic resonance imaging; guidance under remote fields; heat generation; and biodegradation. Yet, this potential is underutilized in that each function manifests at different nanoparticle sizes. Here, sub-micrometer discoidal magnetic nanoconstructs are realized by confining 5 nm ultra-small super-paramagnetic iron oxide nanoparticles (USPIOs) within two different mesoporous structures, made out of silicon and polymers. These nanoconstructs exhibit transversal relaxivities up to ~10 times (r₂ ~ 835 (mM·s)^-1) higher than conventional USPIOs and, under external magnetic fields, collectively cooperate to amplify tumor accumulation. The boost in r₂ relaxivity arises from the formation of mesoscopic USPIO clusters within the porous matrix, inducing a local reduction in water molecule mobility as demonstrated via molecular dynamics simulations. The cooperative accumulation under static magnetic field derives from the large amount of iron that can be loaded per nanoconstuct (up to ~ 65 fg) and the consequent generation of significant inter-particle magnetic dipole interactions. In tumor bearing mice, the silicon-based nanoconstructs provide MRI contrast enhancement at much smaller doses of iron (~ 0.5 mg of Fe/kg animal) as compared to current practice.