Controlled Synthesis of Magnetic Iron Oxide Nanoparticles: Magnetite or Maghemite?

Advances in surface design and biomedical applications of magnetic nanoparticles

Despite significant efforts by scientists in the development of advanced nanotechnology materials for smart diagnosis devices and drug delivery systems, the success of clinical trials remains largely elusive. In order to address this biomedical challenge, magnetic nanoparticles (MNPs) have gained attention as a promising candidate due to their theranostic properties, which allow the simultaneous treatment and diagnosis of a disease. Moreover, MNPs have advantageous characteristics such as a larger surface area, high surface-to-volume ratio, enhanced mobility, mass transference and, more notably, easy manipulation under external magnetic fields. Besides, certain magnetic particle types based on the magnetite (Fe3O4) phase have already been FDA-approved, demonstrating biocompatible and low toxicity. Typically, surface modification and/or functional group conjugation are required to prevent oxidation and particle aggregation. A wide range of inorganic and organic molecules have been utilized to coat the surface of MNPs, including surfactants, antibodies, synthetic and natural polymers, silica, metals, and various other substances. Furthermore, various strategies have been developed for the synthesis and surface functionalization of MNPs to enhance their colloidal stability, biocompatibility, good response to an external magnetic field, etc. Both uncoated MNPs and those coated with inorganic and organic compounds exhibit versatility, making them suitable for a range of applications such as drug delivery systems (DDS), magnetic hyperthermia, fluorescent biological labels, biodetection and magnetic resonance imaging (MRI). Thus, this review provides an update of recently published MNPs works, providing a current discussion regarding their strategies of synthesis and surface modifications, biomedical applications, and perspectives.

Pilot-scale co-precipitation synthesis of a novel active ingredient made of ultrasmall iron (oxyhydr)oxide nanoparticles for the treatment of hyperphosphatemia

Due to its simplicity, co-precipitation is the most commonly used method for producing iron (oxyhydr)oxide nanoparticles. However, it is reported to be sensitive to changes in process parameters, which complicates scale-up and is why only volumes up to 1.2 L have been described in the literature. This study aims to demonstrate the scale-up of a co-precipitation synthesis to 100 L using the example of a new phosphate-binding active ingredient based on iron (oxyhydr)oxide. The synthesis was shown to be very robust to changes in synthesis parameters and stirrer geometries. The in vitro phosphate-binding efficacy and the yield were maintained in all five scales tested. Only the content of the components in the nanoparticles varied slightly. However, Mössbauer spectroscopy, dynamic light scattering (DLS), and attenuated total reflection Fourier transform infrared spectroscopy (FT-IR) revealed no evidence of structural changes, but a reduction in the size of the iron (oxyhydr)oxide cores and the total core-shell nanoparticle sizes. Overall, this study has successfully demonstrated that ultrasmall iron (oxyhydr)oxide nanoparticles can be produced on a pilot scale by co-precipitation with a yield of >40 g L-1.

Specific nanoprobe design for MRI: Targeting laminin in the blood-brain barrier to follow alteration due to neuroinflammation

Chronic neuroinflammation is characterized by increased blood-brain barrier (BBB) permeability, leading to molecular changes in the central nervous system that can be explored with biomarkers of active neuroinflammatory processes. Magnetic resonance imaging (MRI) has contributed to detecting lesions and permeability of the BBB. Ultra-small superparamagnetic particles of iron oxide (USPIO) are used as contrast agents to improve MRI observations. Therefore, we validate the interaction of peptide-88 with laminin, vectorized on USPIO, to explore BBB molecular alterations occurring during neuroinflammation as a potential tool for use in MRI. The specific labeling of NPS-P88 was verified in endothelial cells (hCMEC/D3) and astrocytes (T98G) under inflammation induced by interleukin 1β (IL-1β) for 3 and 24 hours. IL-1β for 3 hours in hCMEC/D3 cells increased their co-localization with NPS-P88, compared with controls. At 24 hours, no significant differences were observed between groups. In T98G cells, NPS-P88 showed similar nonspecific labeling among treatments. These results indicate that NPS-P88 has a higher affinity towards brain endothelial cells than astrocytes under inflammation. This affinity decreases over time with reduced laminin expression. In vivo results suggest that following a 30-minute post-injection, there is an increased presence of NPS-P88 in the blood and brain, diminishing over time. Lastly, EAE animals displayed a significant accumulation of NPS-P88 in MRI, primarily in the cortex, attributed to inflammation and disruption of the BBB. Altogether, these results revealed NPS-P88 as a biomarker to evaluate changes in the BBB due to neuroinflammation by MRI in biological models targeting laminin.

Dramatic change in the properties of magnetite-modified MOF particles depending on the synthesis approach

Iron-containing metal-organic frameworks are promising Fenton catalysts. However, the absence of additional modifiers has proven difficult due to the low reaction rates and the inability to manipulate the catalysts. We hypothesize that the production of iron oxide NPs in the presence of a metal-organic framework will increase the rate of the Fenton reaction and lead to the production of particles that can be magnetically manipulated without changing the structure of the components. A comprehensive approach lead to a metal organic framework using the example of MIL-88b (Materials of Institute Lavoisier) modified with iron oxides NPs: formulation of iron oxide in the presence of MIL-88b and vice versa. The synthesis of MIL-88b consists of preparing a complexation compound with the respective structure and addition of terephthalic acid. The synthesis of MIL-88b facilitates to control the topology of the resulting material. Both methods for composite formulation lead to the preservation of the structure of iron oxide, however, a more technologically complex approach to obtaining MIL-88b in the presence of Fe3O4 suddenly turned out to be the more efficient for the release of iron ions.

Design of hydrophobic polyurethane-magnetite iron oxide-titanium dioxide nanocomposites for oil-water separation

Efficacious oil-water separation has become a global challenge owing to regular oil spillage accidents and escalating industrial oily wastewater. In this study, we synthesized titanium dioxide and magnetite iron oxide nanoparticles to use as a precursor for the production of the nanocomposites. Hydrophobic nanocomposites were fabricated using polyurethane, hematite and magnetite iron oxide nanoparticles, and titanium dioxide nanoparticles through a sol-gel process. The formation of the obtained nanocomposites was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses. In addition, the thermogravimetric and differential thermogravimetric (TGA/DTG) and BET surface area results exhibited enhanced thermal stability of the optimized nanocomposite which displayed mesoporous type materials feature with high porosity. Furthermore, the obtained outcomes demonstrated that the distribution of nanoparticles into a polymer matrix had a significant impact on enhancing superhydrophobicity and the separation efficiency against sunflower oil. Seeing the water contact angle of the nanocomposite-coated filter paper was about 157° compared to 0° for the uncoated filter paper and endowed separation efficiency of almost 90% for 5 consecutive cycles. Thereby, these nanocomposites could be an ideal candidate for self-cleaning surfaces and oil-polluted water purification.

Bioinspired Synthesis of Magnetic Nanoparticles Based on Iron Oxides Using Orange Waste and Their Application as Photo-Activated Antibacterial Agents

Magnetic nanoparticles based on iron oxides (MNPs-Fe) have been proposed as photothermal agents (PTAs) within antibacterial photothermal therapy (PTT), aiming to counteract the vast health problem of multidrug-resistant bacterial infections. We present a quick and easy green synthesis (GS) to prepare MNPs-Fe harnessing waste. Orange peel extract (organic compounds) was used as a reducing, capping, and stabilizing agent in the GS, which employed microwave (MW) irradiation to reduce the synthesis time. The produced weight, physical-chemical features and magnetic features of the MNPs-Fe were studied. Moreover, their cytotoxicity was assessed in animal cell line ATCC RAW 264.7, as well as their antibacterial activity against Staphylococcus aureus and Escherichia coli. We found that the 50GS-MNPs-Fe sample (prepared by GS, with 50% v/v of NH₄OH and 50% v/v of orange peel extract) had an excellent mass yield. Its particle size was ~50 nm with the presence of an organic coating (terpenes or aldehydes). We believe that this coating improved the cell viability in extended periods (8 days) of cell culture with concentrations lower than 250 µg·mL^-1, with respect to the MNPs-Fe obtained by CO and single MW, but it did not influence the antibacterial effect. The bacteria inhibition was attributed to the plasmonic of 50GS-MNPs-Fe (photothermal effect) by irradiation with red light (630 nm, 65.5 mW·cm^-2, 30 min). We highlight the superparamagnetism of the 50GS-MNPs-Fe over 60 K in a broader temperature range than the MNPs-Fe obtained by CO (160.09 K) and MW (211.1 K). Therefore, 50GS-MNPs-Fe could be excellent candidates as broad-spectrum PTAs in antibacterial PTT. Furthermore, they might be employed in magnetic hyperthermia, magnetic resonance imaging, oncological treatments, and so on.

Fabrication of Curcumin Diethyl γ-Aminobutyrate-Loaded Chitosan-Coated Magnetic Nanocarriers for Improvement of Cytotoxicity against Breast Cancer Cells

This study shows the effectiveness of magnetic-guide targeting in the delivery of curcumin diethyl γ-aminobutyrate (CUR-2GE), a prodrug of curcumin (CUR) previously synthesized to overcome unfavorable physicochemical properties of CUR. In this study, chitosan (Ch)-coated iron oxide nanoparticles (Ch-IONPs) were fabricated and optimized using Box-Behnken design-based response surface methodology for delivery of CUR-2GE. Ch was used as a coating material on the nanoparticle surface to avoid aggregation. The optimized condition for preparing Ch-IONPs consisted of using 4 mg Ch fabricated at pH 11 under a reaction temperature of 85 °C. The optimized Ch-IONPs were successfully loaded with CUR-2GE with sufficient loading capacity (1.72 ± 0.01%) and encapsulation efficiency (94.9 ± 0.8%). The obtained CUR-2GE-loaded Ch-IONPs (CUR-2GE-Ch-IONPs) exhibited desirable characteristics including a particle size of less than 50 nm based on TEM images, superparamagnetic property, highly crystalline IONP core, sufficient stability, and sustained-release profile. In the presence of permanent magnets, CUR-2GE-Ch-IONPs significantly increased cellular uptake and cytotoxicity toward MDA-MB-231 with a 12-fold increase in potency compared to free CUR-2GE, indicating the potential of magnetic-field assisted delivery of CUR-2GE-Ch-IONPs for the treatment of triple-negative breast cancer.

Carboxymethyl-Dextran-Coated Superparamagnetic Iron Oxide Nanoparticles for Drug Delivery: Influence of the Coating Thickness on the Particle Properties

Carboxymethyl-dextran (CMD)-coated iron oxide nanoparticles (IONs) are of great interest in nanomedicine, especially for applications in drug delivery. To develop a magnetically controlled drug delivery system, many factors must be considered, including the composition, surface properties, size and agglomeration, magnetization, cytocompatibility, and drug activity. This study reveals how the CMD coating thickness can influence these particle properties. ION@CMD are synthesized by co-precipitation. A higher quantity of CMD leads to a thicker coating and a reduced superparamagnetic core size with decreasing magnetization. Above 12.5−25.0 g L−1 of CMD, the particles are colloidally stable. All the particles show hydrodynamic diameters < 100 nm and a good cell viability in contact with smooth muscle cells, fulfilling two of the most critical characteristics of drug delivery systems. New insights into the significant impact of agglomeration on the magnetophoretic behavior are shown. Remarkable drug loadings (62%) with the antimicrobial peptide lasioglossin and an excellent efficiency (82.3%) were obtained by covalent coupling with the EDC/NHS (N-ethyl-N′-(3-(dimethylamino)propyl)carbodiimide/N-hydroxysuccinimide) method in comparison with the adsorption method (24% drug loading, 28% efficiency). The systems showed high antimicrobial activity with a minimal inhibitory concentration of 1.13 µM (adsorption) and 1.70 µM (covalent). This system successfully combines an antimicrobial peptide with a magnetically controllable drug carrier.

Magnetic Iron Nanoparticles: Synthesis, Surface Enhancements, and Biological Challenges

This review focuses on the role of magnetic nanoparticles (MNPs), their physicochemical properties, their potential applications, and their association with the consequent toxicological effects in complex biologic systems. These MNPs have generated an accelerated development and research movement in the last two decades. They are solving a large portion of problems in several industries, including cosmetics, pharmaceuticals, diagnostics, water remediation, photoelectronics, and information storage, to name a few. As a result, more MNPs are put into contact with biological organisms, including humans, via interacting with their cellular structures. This situation will require a deeper understanding of these particles’ full impact in interacting with complex biological systems, and even though extensive studies have been carried out on different biological systems discussing toxicology aspects of MNP systems used in biomedical applications, they give mixed and inconclusive results. Chemical agencies, such as the Registration, Evaluation, Authorization, and Restriction of Chemical substances (REACH) legislation for registration, evaluation, and authorization of substances and materials from the European Chemical Agency (ECHA), have held meetings to discuss the issue. However, nanomaterials (NMs) are being categorized by composition alone, ignoring the physicochemical properties and possible risks that their size, stability, crystallinity, and morphology could bring to health. Although several initiatives are being discussed around the world for the correct management and disposal of these materials, thanks to the extensive work of researchers everywhere addressing the issue of related biological impacts and concerns, and a new nanoethics and nanosafety branch to help clarify and bring together information about the impact of nanoparticles, more questions than answers have arisen regarding the behavior of MNPs with a wide range of effects in the same tissue. The generation of a consolidative framework of these biological behaviors is necessary to allow future applications to be manageable.

A guide to the design of magnetic particle imaging tracers for biomedical applications

Magnetic Particle Imaging (MPI) is a novel and emerging non-invasive technique that promises to deliver high quality images, no radiation, high depth penetration and nearly no background from tissues. Signal intensity and spatial resolution in MPI are heavily dependent on the properties of tracers. Hence the selection of these nanoparticles for various applications in MPI must be carefully considered to achieve optimum results. In this review, we will provide an overview of the principle of MPI and the key criteria that are required for tracers in order to generate the best signals. Nanoparticle materials such as magnetite, metal ferrites, maghemite, zero valent iron@iron oxide core@shell, iron carbide and iron-cobalt alloy nanoparticles will be discussed as well as their synthetic pathways. Since surface modifications play an important role in enabling the use of these tracers for biomedical applications, coating options including the transfer from organic to inorganic media will also be discussed. Finally, we will discuss different biomedical applications and provide our insights into the most suitable tracer for each of these applications.

Synthesis of Water-Dispersed Sulfobetaine Methacrylate-Iron Oxide Nanoparticle-Coated Graphene Composite by Free Radical Polymerization

Research on the synthesis of water-soluble polymers has accelerated in recent years, as they are employed in many bio-applications. Herein, the synthesis of poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PSB) by free radical polymerization in a sonication bath is described. PSB and iron oxide nanoparticles (IONPs) were simultaneously stabilized on the graphene surface. Graphene surfaces with PSB (GPSB) and graphene surfaces with PSB and IONPs (GPSBI) were prepared. Since PSB is a water-soluble polymer, the hydrophobic nature of graphene surfaces converts to hydrophilic nature. Subsequently, the prepared graphene composites, GPSB and GPSBI, were well-dispersed in water. The preparation of GPSB and GPSBI was confirmed by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The impacts of PSB and IONPs on the graphene surfaces were studied systematically.

A New Design for Magnetic Poly(vinyl pivalate) for Biomedical Applications: Synthesis, Characterization, and Evaluation of Cytotoxicity in Fibroblasts, Keratinocytes, and Human Melanoma Cells

Polymers containing magnetic properties play an important role in biomedical therapies, such as embolotherapy or hyperthermia, for their differentiated properties. In this work, magnetite (Fe3O4) nanoparticles were synthesized by the coprecipitation method and dispersed into a thermoplastic matrix of poly(vinyl pivalate) through an emulsion polymerization process. The main goal was the individual encapsulation of magnetite nanoparticles to improve the magnetic response of the magneto-polymeric materials using polymerizable carboxylic acids as coating agents, minimizing the leaching of nanoparticles throughout the nanocomposite formation. For this purpose, synthesized magnetite had its surface modified by acrylic acid or methacrylic acid to improve its individual encapsulation during the polymerization step, thus generating a series of magnetic nanocomposite materials containing different amounts of magnetite intended for biomedical applications. X-ray diffractometry and TEM measurements provided a mean size of approximately 8 nm for the pure magnetite nanoparticles and a spherical morphology. Acid-functionalized Fe3O4 had a size of approximately 6 nm, while the nanocomposites showed a size of approximately 7 nm. Magnetization measurement provided a saturation magnetization value of approximately 75 emu/g and confirmed superparamagnetic behavior at room temperature. DSC analysis showed a glass transition temperature of 65 °C for poly(vinyl pivalate)-based nanocomposites. The tests realized with homopolymer and magnetic composites against different cell lineages (i.e., fibroblasts, keratinocytes, and human melanoma) to evaluate the levels of cytotoxicity showed good results in the different exposure times and concentrations used, since the obtained results showed cell viability greater than 70% compared to the control group, suggesting that the synthesized materials are very promising for medical applications.

Magnetic/flow controlled continuous size fractionation of magnetic nanoparticles using simulated moving bed chromatography

The use of magnetic nanoparticles shows a steadily increasing technical importance. Particularly in medical technology disciplines such as cancer treatment, the potential of these special particles is increasing rapidly. Magnetic nanoparticles are particles with a submicron size, and consist mostly of magnetite-containing composites. An important quality parameter of such particles is a particle size distribution as narrow as possible, which can only be obtained to a certain degree by synthesis. Apart from ultracentrifugation, there are so far only methods on an analytical scale to narrow the size distribution as a post-processing step. We present a method based on magnetic chromatography, by which high separation efficiencies at yields of up to 99.9% are achieved. The novel technique is based on a competition between the magnetic interaction of the nanoparticles and the separation matrix, as well as the hydrodynamic forces. Furthermore, the method is extended using a continuous mode, namely simulated moving bed chromatography, to obtain potent space-time yields of up to 2.94 g/(L*h). For those reasons, this novel continuous magnetic chromatography method offers high potential for large-scale refinement of magnetic nanoparticles while fulfilling sophisticated quality criteria for high-technology applications.

Optimization of Magnetic Nanoparticles Draw Solution for High Water Flux in Forward Osmosis

In this study, bare iron oxide nanoparticles were synthesized using a co-precipitation method and used as a draw solute in forward osmosis. The synthesis conditions of the nanoparticles were optimized using the Box-Behnken method to increase the water flux of the forward osmosis process. The studied parameters were volume of ammonia solution, reaction temperature, and reaction time. The optimum reaction conditions were obtained at reaction temperature of 30 °C, reaction time of 2.73 h and 25.3 mL of ammonia solution. The water flux from the prediction model was found to be 2.06 LMH which is close to the experimental value of 1.98 LMH. The prediction model had high correlation factors (R2 = 98.82%) and (R2adj = 96.69%). This study is expected to be the base for future studies aiming at developing magnetic nanoparticles draw solution using co-precipitation method.

Immunomodulatory and anti-inflammatory efficacy of hederagenin-coated maghemite (γ-Fe2O3) nanoparticles in an atopic dermatitis model

We investigated the immunomodulatory and anti-inflammatory efficacy of hederagenin coating on maghemite (γ-Fe₂O₃) nanoparticles (HM) in atopic dermatitis (AD), as well as the physical and optical properties of maghemite nanoparticles (MP) using SEM, XRD spectroscopy, UV-vis spectra, Raman spectra, and FTIR spectroscopy. Dose-dependent treatment with HM (10, 50, 100, 200 μg/mL) inhibited the expression of Interleukin-2 (IL-2) and Tumor necrosis factor- α (TNF-α) in inflammatory induced HaCaT and Jurkat cells with inflammation caused by TNF/IFN-γ and PMA/A23187. AD model was induced by performing topical application of 2,4-dinitrochlorobenzene (DNCB) and dermatophagoides farinae extract (DFE) for a 31-day period on 8-week-old BALB/c mice. The HM treatments efficiently diminished the AD-like cutaneous lesion induced by DNCB-DFE sensitization in mice. Compared to the AD-only groups, HM treatment considerably attenuated mast cell infiltration and lowered epidermal, and dermal thickness of mice ears skin. In addition, HM treatment prominently alleviated the enlarged size and weight of lymph nodes. Furthermore, HM treatment resulted in a notable reduction in the mRNA expression of Th1 cytokines (TNF-α and IFN-γ), Th2 cytokines (IL-4 and IL-6), Th17 (IL-17), and TSLP. Our data showed that HM provides better AD attenuation compared to MP. Additionally, HM had synergistic effect and act as anti-inflammatory and immunomodulatory agent. Thus, HM shows great potential in AD medication and as a substitution of non-steroid-based medication.

One-Pot Synthesis of Multiple Stimuli-Responsive Magnetic Nanomaterials Based on the Biomineralization of Elastin-like Polypeptides

Synthesis of multiple stimuli-responsive magnetic nanomaterials in a green way remains as a big challenge currently. Herein, temperature-responsive elastin-like polypeptides (ELPs) were designed to involve in the biomimetic mineralization and successfully prepared magnetic nanoparticles (MNPs) (named ELPs-MNPs) with multiple responsiveness (temperature, magnetic, and biomimetic silicification responsiveness) in one pot. ELPs-MNPs were identified as cubic nanomaterials with an average size of about 32 nm and in line with the classic ferromagnetic behavior. Interestingly, ELPs-MNPs show clearly lower critical solution temperature phase behavior with a transition temperature of 36 °C. Moreover, ELPs-MNPs can spontaneously trigger the biosilicification of tetramethyl orthosilicate (TMOS) to entrap themselves into silicon oxide as proved by the Fourier transform infrared spectra (FTIR) and elemental mapping of transmission electron microscopy (TEM), with an average size of about 62 nm. The possible role of ELPs in the biomimetic preparation of the multiple stimuli-responsive MNPs was also addressed. The proposed novel and simple one-pot strategy to synthesize multifunctional nanomaterials with higher effectiveness is the first report for preparing MNPs with multiple stimuli response. This strategy conforms to the concept of green chemistry and will pave a new way for the design of smart biomaterials, which may have great potentials for different fields.

Nanobiotechnology-assisted therapies to manage brain cancer in personalized manner

There are numerous investigated factors that limit brain cancer treatment efficacy such as ability of prescribed therapy to cross the blood-brain barrier (BBB), tumor specific delivery of a therapeutics, transport within brain interstitium, and resistance of tumor cells against therapies. Recent breakthroughs in the field of nano-biotechnology associated with developing multifunctional nano-theranostic emerged as an effective way to manage brain cancer in terms of higher efficacy and least possible adverse effects. Keeping challenges and state-of-art accomplishments into consideration, this review proposes a comprehensive, careful, and critical discussion focused on efficient nano-enabled platforms including nanocarriers for drug delivery across the BBB and nano-assisted therapies (e.g., nano-immunotherapy, nano-stem cell therapy, and nano-gene therapy) investigated for brain cancer treatment. Besides therapeutic efficacy point-of-view, efforts are being made to explore ways projected to tune such developed nano-therapeutic for treating patients in personalized manner via controlling size, drug loading, delivery, and retention. Personalized brain tumor management based on advanced nano-therapies can potentially lead to excellent therapeutic benefits based on unique genetic signatures in patients and their individual disease profile. Moreover, applicability of nano-systems as stimulants to manage the brain cancer growth factors has also been discussed in photodynamic therapy and radiotherapy. Overall, this review offers a comprehensive information on emerging opportunities in nanotechnology for advancing the brain cancer treatment.

Differentiating Nanomaghemite and Nanomagnetite and Discussing Their Importance in Arsenic and Lead Removal from Contaminated Effluents: A Critical Review

Arsenic and lead heavy metals are polluting agents still present in water bodies, including surface (lake, river) and underground waters; consequently, the development of new adsorbents is necessary to uptake these metals with high efficiency, quick and clean removal procedures. Magnetic nanoparticles, prepared with iron-oxides, are excellent candidates to achieve this goal due to their ecofriendly features, high catalytic response, specific surface area, and pulling magnetic response that favors an easy removal. In particular, nanomagnetite and maghemite are often found as the core and primary materials regarding magnetic nanoadsorbents. However, these phases show interesting distinct physical properties (especially in their surface magnetic properties) but are not often studied regarding correlations between the surface properties and adsorption applications, for instance. Thus, in this review, we summarize the main characteristics of the co-precipitation and thermal decomposition methods used to prepare the nano-iron-oxides, being the co-precipitation method most promising for scaling up processes. We specifically highlight the main differences between both nano-oxide species based on conventional techniques, such as X-ray diffraction, zero and in-field Mössbauer spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism, the latter two techniques performed with synchrotron light. Therefore, we classify the most recent magnetic nanoadsorbents found in the literature for arsenic and lead removal, discussing in detail their advantages and limitations based on various physicochemical parameters, such as temperature, competitive and coexisting ion effects, i.e., considering the simultaneous adsorption removal (heavy metal-heavy metal competition and heavy metal-organic removal), initial concentration, magnetic adsorbent dose, adsorption mechanism based on pH and zeta potential, and real water adsorption experiments. We also discuss the regeneration/recycling properties, after-adsorption physicochemical properties, and the cost evaluation of these magnetic nanoadsorbents, which are important issues, but less discussed in the literature.

Effect of Citrate on the Size and the Magnetic Properties of Primary Fe3O4 Nanoparticles and Their Aggregates

The size, size distribution and magnetic properties of magnetite nanoparticles (NPs) prepared by co-precipitation without citrate, in the presence of citrate and citrate adsorbed post-synthesis were studied by X-ray Diffraction (XRD), Dynamic Light Scattering (DLS), Electron Paramagnetic Resonance (EPR) and magnetization measurements. The aim of this investigation was to clarify the effect of citrate ions on the size and magnetic properties of magnetite NPs. The size of the primary NPs, as determined by analysing the width of diffraction peaks using various methods, was ca. 10 nm for bare magnetite NPs and with citrate adsorbed post-synthesis, whereas it was around 5 nm for the NPs co-precipitated in the presence of citrate. DLS measurements show that the three types of NPs form aggregates (100–200 nm in diameter) but the dispersions of the citrate-coated NPs are more stable against sedimentation than those of bare NPs. The sizes and size distributions determined by XRD are in good agreement with those of the magnetic domains obtained by fitting of the magnetization vs. magnetic field intensity curves. Magnetization vs. magnetic field intensity curves show that the three kinds of sample are superparamagnetic.

Advanced biomedical applications of iron oxide nanostructures based ferrofluids

Ferrofluids or magnetic nanofluids are highly stable colloidal suspensions of magnetic nanoparticles (NPs) dispersed into various base fluids. These stable ferrofluids possess high thermal conductivity, improved thermo-physical properties, higher colloidal stability, good magnetic properties, and biocompatibility, which are the primary driving forces behind their excellent performance, and thus enable them to be used for a wide range of practical applications. The most studied and advanced ferrofluids are based on iron oxide nanostructures especially NPs, because of their easy and large-scale synthesis at low costs. Although in the last decade, several review articles are available on ferrofluids but mainly focused on preparations, properties, and a specific application. Hence, a collective and comprehensive review article on the recent progress of iron oxide nanostructures based ferrofluids for advanced biomedical applications is undeniably required. In this review, the state of the art of biomedical applications is presented and critically analyzed with a special focus on hyperthermia, drug delivery/nanomedicine, magnetic resonance imaging, and magnetic separation of cells. This review article provides up-to-date information related to the technological advancements and emerging trends in iron oxide nanostructures based ferrofluids research focused on advanced biomedical applications. Finally, conclusions and outlook of iron oxide nanostructures based ferrofluids research for biomedical applications are presented.

The Effect of pH and Viscosity on Magnetophoretic Separation of Iron Oxide Nanoparticles

Magnetic nanoparticles (MNPs) are used for magnetophoresis-based separation processes in various biomedical and engineering applications. Essential requirements are the colloidal stability of the MNPs and the ability to be separated even in low magnetic field gradients. Bare iron oxide nanoparticles (BIONs) with a diameter of 9.2 nm are synthesized via coprecipitation, exhibiting a high saturation magnetization of 70.84 Am2 kg−1 and no remanence. In our study, zeta potential, dynamic light scattering (DLS), and sedimentation analysis show that the aggregation behavior of BIONs is influenced by pH and viscosity. Small aggregate clusters are formed with either low or high pH values or increased viscosity. Regarding magnetophoresis-based separation, a higher viscosity leads to lower magnetophoretic velocities, similar to how small aggregates do. Additionally, cooperative magnetophoresis, the joint motion of strongly interacting particles, affects the separation of the BIONs, too. Our study emphasizes the effect of pH and viscosity on the physicochemical characteristics of MNPs, resulting in different aggregation behavior. Particularly, for high viscous working media in downstream processing and medicine, respectively, the viscosity should be taken into account, as it will affect particle migration.

Fabrication, Microstructure and Colloidal Stability of Humic Acids Loaded Fe3O4/APTES Nanosorbents for Environmental Applications

Nowadays, numerous researches are being performed to formulate nontoxic multifunctional magnetic materials possessing both high colloidal stability and magnetization, but there is a demand in the prediction of chemical and colloidal stability in water solutions. Herein, a series of silica-coated magnetite nanoparticles (MNPs) has been synthesized via the sol-gel method with and without establishing an inert atmosphere, and then it was tested in terms of humic acids (HA) loading applied as a multifunctional coating agent. The influence of ambient conditions on the microstructure, colloidal stability and HA loading of different silica-coated MNPs has been established. The XRD patterns show that the content of stoichiometric Fe₃O₄ decreases from 78.8% to 42.4% at inert and ambient atmosphere synthesis, respectively. The most striking observation was the shift of the MNPs isoelectric point from pH ~7 to 3, with an increasing HA reaching up to the reversal of the zeta potential sign as it was covered completely by HA molecules. The zeta potential data of MNPs can be used to predict the loading capacity for HA polyanions. The data help to understand the way for materials’ development with the complexation ability of humic acids and with the insolubility of silica gel to pave the way to develop a novel, efficient and magnetically separable adsorbent for contaminant removal.

Magnetically Induced Aggregation of Iron Oxide Nanoparticles for Carrier Flotation Strategies

On the nanoscale, iron oxides can be used for multiple applications ranging from medical treatment to biotechnology. We aimed to utilize the specific properties of these nanoparticles for new process concepts in flotation. Magnetic nanoparticles were synthesized by alkaline coprecipitation, leading to a primary particle size of 9 nm, and coated with oleate. The nanomaterial was characterized for its superparamagnetism and its colloidal stability at different ionic strengths, with and without an external magnetic field. The nanomaterial was used for model experiments on magnetic carrier flotation of microplastic particles, based on magnetically induced heteroagglomeration. We were able to demonstrate the magnetically induced aggregation of the nanoparticles which allows for new flotation strategies. Since the nanomaterial has zero remanent magnetization, the agglomeration is reversible which facilitates the process control. Magnetic carrier flotation based on iron oxide nanoparticles can pave the way to promising new recycling processes for microplastic wastes.

Iron Oxide Nanoparticles: Multiwall Carbon Nanotube Composite Materials for Batch or Chromatographic Biomolecule Separation

Carbon-based materials are the spearhead of research in multiple fields of nanotechnology. Moreover, their role as stationary phase in chromatography is gaining relevance. We investigate a material consisting of multiwall carbon nanotubes (CNTs) and superparamagnetic iron oxide nanoparticles towards its use as a mixed-mode chromatography material. The idea is to immobilize the ion exchange material iron oxide on CNTs as a stable matrix for chromatography processes without a significant pressure drop. Iron oxide nanoparticles are synthesized and used to decorate the CNTs via a co-precipitation route. They bind to the walls of oxidized CNTs, thereby enabling to magnetically separate the composite material. This hybrid material is investigated with transmission electron microscopy, magnetometry, X-ray diffraction, X-ray photoelectron and Raman spectroscopy. Moreover, we determine its specific surface area and its wetting behavior. We also demonstrate its applicability as chromatography material for amino acid retention, describing the adsorption and desorption of different amino acids in a complex porous system surrounded by aqueous media. Thus, this material can be used as chromatographic matrix and as a magnetic batch adsorbent material due to the iron oxide nanoparticles. Our work contributes to current research on composite materials. Such materials are necessary for developing novel industrial applications or improving the performance of established processes.

Sample preparation considerations for surface and crystalline properties and ecotoxicity of bare and silica-coated magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticles (NPs) have widely used in various fields, including in medicine, due to their (super)paramagnetic properties. This requires a thorough evaluation of their possible hazardous effects. However, there is no standard procedure for the preparation of oxidation-prone NPs (such as magnetite) before subjecting them to biological assays. In this study we used Fe₃O₄ NPs (bare and silica-coated) as test samples to compare different preparation methods (ultrasound, centrifugation and filteration of NPs suspensions) based on X-ray and dynamic light scattering analysis and evaluation of microstructure and surface charge. After oxidation and functionalization, all samples retained their superparamagnetic behaviour. The toxicity of NP suspensions obtained by the methods described for Paramecium caudatum ciliates and Sinapis alba plants was evaluated.

The charge and surface reactivity of magnetite nanoparticles can be affected by the different separation methods leading to their toxicity changes.

Magnetic Iron Oxide Nanoparticle (IONP) Synthesis to Applications: Present and Future

Iron oxides are chemical compounds which have different polymorphic forms, including γ-Fe2O3 (maghemite), Fe3O4 (magnetite), and FeO (wustite). Among them, the most studied are γ-Fe2O3 and Fe3O4, as they possess extraordinary properties at the nanoscale (such as super paramagnetism, high specific surface area, biocompatible etc.), because at this size scale, the quantum effects affect matter behavior and optical, electrical and magnetic properties. Therefore, in the nanoscale, these materials become ideal for surface functionalization and modification in various applications such as separation techniques, magnetic sorting (cells and other biomolecules etc.), drug delivery, cancer hyperthermia, sensing etc., and also for increased surface area-to-volume ratio, which allows for excellent dispersibility in the solution form. The current methods used are partially and passively mixed reactants, and, thus, every reaction has a different proportion of all factors which causes further difficulties in reproducibility. Direct active and complete mixing and automated approaches could be solutions to this size- and shape-controlled synthesis, playing a key role in its exploitation for scientific or technological purposes. An ideal synthesis method should be able to allow reliable adjustment of parameters and control over the following: fluctuation in temperature; pH, stirring rate; particle distribution; size control; concentration; and control over nanoparticle shape and composition i.e., crystallinity, purity, and rapid screening. Iron oxide nanoparticle (IONP)-based available clinical applications are RNA/DNA extraction and detection of infectious bacteria and viruses. Such technologies are important at POC (point of care) diagnosis. IONPs can play a key role in these perspectives. Although there are various methods for synthesis of IONPs, one of the most crucial goals is to control size and properties with high reproducibility to accomplish successful applications. Using multiple characterization techniques to identify and confirm the oxide phase of iron can provide better characterization capability. It is very important to understand the in-depth IONP formation mechanism, enabling better control over parameters and overall reaction and, by extension, properties of IONPs. This work provides an in-depth overview of different properties, synthesis methods, and mechanisms of iron oxide nanoparticles (IONPs) formation, and the diverse range of their applications. Different characterization factors and strategies to confirm phase purity in the IONP synthesis field are reviewed. First, properties of IONPs and various synthesis routes with their merits and demerits are described. We also describe different synthesis strategies and formation mechanisms for IONPs such as for: wustite (FeO), hematite (α-Fe2O3), maghemite (ɤ-Fe2O3) and magnetite (Fe3O4). We also describe characterization of these nanoparticles and various applications in detail. In conclusion, we present a detailed overview on the properties, size-controlled synthesis, formation mechanisms and applications of IONPs.

Green Synthesis, Characterization and Application of Natural Product Coated Magnetite Nanoparticles for Wastewater Treatment

Adsorption of organic pollutants, toxic metal ions, and removal of harmful bacteria can give us clean and pure drinkable water from wastewater resources. Respective magnetite nanoparticles (MNPs) were synthesized using a cheaper and greener way in an open-air environment with the use of crude latex of Jatropha curcas (JC) and leaf extract of Cinnamomum tamala (CT). Characterization of MNPs had been performed by dynamic light scattering (DLS), Ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, powdered X-ray diffraction (XRD), and field emission scanning electron microscope (FE-SEM). The size ranges of the synthesized MNPs were observed in between 20-42 nm for JC-Fe₃O₄ and within 26-35 nm for CT-Fe₃O₄ by FE-SEM images. The effect of synthesized magnetic nanoparticles in wastewater treatment (bacterial portion), dye adsorption, toxic metal removal as well as antibacterial, antioxidant, and cytotoxic activities were studied. This purification will lead to an increase in the resources of pure drinking water in the future.

Synthesis and Characterization of Amorphous Iron Oxide Nanoparticles by the Sonochemical Method and Their Application for the Remediation of Heavy Metals from Wastewater

Nanoparticles have gained huge attention in the last decade due to their applications in electronics, medicine, and environmental clean-up. Iron oxide nanoparticles (IONPs) are widely used for the wastewater treatment due to their recyclable nature and easy manipulation by an external magnetic field. Here, in the present research work, iron oxide nanoparticles were synthesized by the sonochemical method by using precursors of ferrous sulfate and ferric chloride at 70 °C for one hour in an ultrasonicator. The synthesized iron oxide nanoparticles were characterized by diffraction light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), electron diffraction spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). The FTIR analysis exhibits characteristic absorption bands of IONPs at 400-800 cm-1, while the Raman spectra showed three characteristic bands at 273, 675, and 1379 cm-1 for the synthesized IONPs. The XRD data revealed three major intensity peaks at two theta, 33°, 35°, and 64° which indicated the presence of maghemite and magnetite phase. The size of the spherical shaped IONPs was varying from 9-70 nm with an average size of 38.9 nm while the size of cuboidal shaped particle size was in microns. The purity of the synthesized IONPs was confirmed by the EDS attached to the FESEM, which clearly show sharp peaks for Fe and O, while the magnetic behavior of the IONPs was confirmed by the VSM measurement and the magnetization was 2.43 emu/g. The batch adsorption study of lead (Pb) and chromium (Cr) from 20% fly ash aqueous solutions was carried out by using 0.6 mg/100 mL IONPs, which exhibited maximum removal efficiency i.e., 97.96% and 82.8% for Pb2+ and Cr ions, respectively. The fly ash are being used in making cements, tiles, bricks, bio fertilizers etc., where the presence of fly ash is undesired property which has to be either removed or will be brought up to the value of acceptable level in the fly ash. Therefore, the synthesized IONPs, can be applied in the elimination of heavy metals and other undesired elements from fly ash with a short period of time. Moreover, the IONPs that have been used as a nanoadsorbent can be recovered from the reaction mixture by applying an external magnetic field that can be recycled and reused. Therefore, this study can be effective in all the fly ash-based industries for elimination of the undesired elements, while recyclability and reusable nature of IONPs will make the whole adsorption or elimination process much economical.