Multicore Nanoparticles Research Articles

Microwave susceptibility analysis of ultrafast moment dynamics in a multicore magnetic nanoparticle system

Room-temperature magnetization dynamics of multicore magnetic nanoparticles often account for intrinsic dipolar magnetism to behave as a single macrospin at low-frequency regime. Either magnetic particle imaging or hyperthermia benefits from the resulting superparamagnetism in terms of nonlinear magnetization response and relaxation losses at frequencies where the rotation of magnetic moments dominates over Brownian motion for a given sinusoidal field. For this situation, spontaneous thermal relaxation (in the absence of external fields) of each composing particle moment within the cluster is critical to define effective Néel time constant and may intersect with ferromagnetic resonance (FMR) at GHz range. Here, we performed broadband AC susceptometry on both immobilized single-core and multicore iron-oxide nanoparticles up to 26.5GHz under DC bias fields. For each solid sample, we confirmed FMR frequency, where large single-core nanoparticle systems demonstrated typical resonance blueshift as DC field increased. Interestingly, high DC field induced the secondary satellite peak in the imaginary part of AC susceptibility spectra for the case of multicore nanoparticle systems. We further highlighted that a synchronous precession of the polarized macrospins under nonuniform effective fields was responsible for splitting FMR peaks at nearby microwave frequencies. Upon curve fitting of the field-dependent FMR frequency spectra, the Landau-Lifshitz-Gilbert-Kittel model later elaborates on the complex moment dynamics of multicore nanoparticle systems in correlation with distribution functions. Published by the American Physical Society 2024

Magnetic Harvesting and Degradation of Microplastics using Iron Oxide Nanoflowers prepared by a Scaled-up Procedure

Addressing the ecological risks and human health threats posed by emerging contaminants requires the development of reproducible and scalable materials and technologies. In this context, the performance of multicore flower-shaped nanoparticles (NFs) with approximately 40 nm diameters was assessed for extracting and degrading polyethylene microplastics from cosmetics in water samples. These NFs, exhibiting cooperative magnetic behavior and high magnetic moment per particle, were scaled to grams of product in a larger reactor (1 L), yielding a 91 % mean reproducibility for structural, colloidal and magnetic properties. The NFs were directly attached to microplastic surfaces via ultrasonic treatment and separated using a permanent magnet, demonstrating removal capacities of up to 1000 mgMP/gNF under optimal conditions (pH 7, 10 mg NFs, 30 min, field strength 320 kA/m). Subsequently, microplastics in aqueous suspensions were hydrolyzed at 150 °C followed by mineralization through a Fenton-like reaction catalyzed by the NFs where reactive oxygen species produced, in the presence of H2O2, break the organic molecules. Mineralization yields ranged from 20 % to 75 % at 25 and 90 °C, respectively, with a further increase to 78 % achieved under an alternating magnetic field (60 mT, 100 kHz), obviating the need for high temperatures. These results highlight the potential of NFs and associated technologies in effectively addressing the challenges associated with emerging contaminants, offering promising avenues for environmental remediation and human health protection.

Design and evaluation of multi-core raspberry-like platinum nanoparticles for enhanced photothermal treatment

While gold-based nanoparticles are now commonly used in nanomedicine due to their stability and high plasmonic resonance, platinum nanoparticles are recently emerging as promising candidates for enhancing radiotherapy sensitivity due to their high atomic number. Here, we demonstrate that platinum-based nanomaterials with a multi-core structure also possess efficient near-infrared photothermal properties, despite platinum’s maximum absorption being primarily in the ultraviolet region. The photothermal efficacy of these platinum multi-core raspberry-like nanoparticles is compared with single-core ultra-small platinum nanoseeds, within glioblastoma cancer spheroids, showcasing the potential of platinum nanocore aggregation for photothermal therapy in cancer treatment. Additionally, we used a microfabrication technique for high-throughput growth of spheroids in microwells to evaluate photothermal treatment on glioblastoma spheroids. Finally, X-ray absorption spectroscopy was conducted to analyze the stability and behavior of both nanoparticles in the cellular environment, indicating their excellent biostability. Moreover, even after laser application, none of the nanoparticles degraded but instead underwent reshaping into a more crystalline structure.

Comprehensive characterization and development of multi-core shell superparamagnetic nanoparticles for controlled delivery of drugs and their kinetic release modelling

The nanoparticles designed for application in cancer treatment should have biocompatibility, colloidal stability and triggered release at tumor sites. Magnetic nanoparticles arise as an interesting option to be used as drug nanocarriers, considering the possibility of driving nanoparticles to the correct delivery site and exploring different triggers to achieve such accomplishment. In this study, nickel ferrite nanoparticles are explored as a magnetic core for drug delivery systems, using doxorubicin and omeprazole as model drugs. The developed nickel ferrite presents a strong superparamagnetic behavior and high purity, as demonstrated by magnetometry and TGA results. The carbon-coating procedure and functionalization allowed the nanoparticle to achieve the desired characteristics for biomedical applications (i.e. stability in water, biocompatibility, and size). According to TEM results, the final carbon-coated magnetic nanoparticles have an average size of 25.09 ± 0.58 nm and multi-core shell architecture, which is suitable for biomedical applications as drug nanocarriers. In addition, DLS demonstrated that functionalized nanoparticles are monodisperse, with a hydrodynamic diameter of 167 ± 59 nm, which fits the recommended range (100–200 nm) to benefit from enhanced permeability and retention effect. Drug loading tests with doxorubicin and omeprazole revealed the versatility of the designed nanoparticles, able to load 97% of doxorubicin and 51% of omeprazole. The pH-triggered release was also confirmed for both pharmacological compounds, showing a higher cumulative drug under acidic conditions (simulating a tumor microenvironment). Finally, the kinetic analysis applied to the study of the release mechanism of both medicines showed that non-linear models fit with higher accuracy the experimental data.

Hybrid multi-core shell magnetic nanoparticles for wet peroxide oxidation of paracetamol: Application in synthetic and real matrices

Clean water availability is becoming a matter of global concern in the last decades. The responsible entities for wastewater treatment do not have the proper facilities to deal with a wide range of pollutants. Special attention should be given to emerging contaminants, whose presence in water bodies may cause adverse effects on the aquatic ecosystem and human health. Most studies in the literature do not consider the development of their solution in real matrices, which can hinder the applicability of the explored alternative in the real scenario. Therefore, in this work, we demonstrate the applicability of hybrid magnetic nanoparticles for removing paracetamol (PCM) from simulated and real matrices by catalytic wet peroxide oxidation (CWPO). To achieve carbon coating, the nanoparticles were prepared via the traditional route (resorcinol/formaldehyde, CoFe@CRF). A new methodology was also considered for synthesizing thin-layered carbon-coated magnetic nanoparticles (phloroglucinol/glyoxalic acid, CoFe@CPG). TEM images revealed a multi-core shell structure formation, with an average carbon layer size of 7.8 ± 0.5 and 3.2 ± 0.3 nm for resorcinol/formaldehyde and phloroglucinol/glyoxalic acid methodology, respectively. Screening the materials’ activity for PCM oxidation by CWPO revealed that the nanoparticle prepared by phloroglucinol/glyoxalic acid methodology has higher performance for the degradation of PCM, achieving 63.5% mineralization after 24 h of reaction, with similar results for more complex matrices. Iron leaching measured at the end of all reactions has proven that the carbon layer protects the core against leaching.

Multi-core shell nanoparticles for efficient removal of nitrophenols from contaminated streams

This study aims to investigate the application of multi-core shell nanoparticles in heterogeneous Fenton processes for efficient removal of specific nitrophenols (2 and 4-nitrophenol) from contaminated wastewater. The synthesis of superparamagnetic magnetite (Fe3O4) was achieved through solution combustion synthesis (SCS) using a citric acid and iron nitrate solution. The mFe3O4@C catalyst was obtained via an adapted Stöber procedure. The material was characterized to identify specific chemical compositions related to the formation of the multi-core shell desired architecture. The carbon coated catalyst exhibited superior performance compared to the bare core catalyst, leading to notable increases in the removal of 2-NP and 4-NP. Moreover, the decomposition of H2O2 was significantly enhanced, indicating the system's potential in efficiently breaking down hazardous compounds. The findings of this study highlight the tremendous potential of the system as a highly effective and viable alternative for the efficient cleansing of contaminated streams polluted with 2-nitrophenol and 4nitrophenol.

Colloidal stability and rheological properties of bio-ferrofluids of polymer-coated single-core and multi-core nanoparticles

The polymethacrylic acid (PMAA)-coated magnetite nanoparticles with single and multi-cores were prepared by the emulsifier-free emulsion polymerization of methacrylic acid (MAA) monomers. X-ray diffraction analysis (XRD), Fourier transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM) were used to identify the nanoparticles and the polymer layer. The coated particles have spherical shapes. The single core diameter is 6.6 nm, and the multi-core diameter is 33.8 nm, with the number of cores in a particle of 131. The PMAA layer thickness is around 4 nm for both coated particles. This polymer layer enhances nanoparticles' dispersion ability while retaining their magnetic properties much higher than in other studies. The coated multi-core particles show excellent dispersion stability. The aggregation rate of these particles is hundreds of times lower than that of single-core particles. All the nanofluids exhibit shear-thinning behavior without and with an external magnetic field. The field-dependent viscosity agrees with the theory regarding the interaction parameter λ. However, the magneto-viscous of the magnetic fluids here are much smaller than comparable bio-ferrofluids.

Cellular and Molecular Processes Are Differently Influenced in Primary Neural Cells by Slight Changes in the Physicochemical Properties of Multicore Magnetic Nanoparticles

Herein, we use two exemplary superparamagnetic iron oxide multicore nanoparticles (SPIONs) to illustrate the significant influence of slightly different physicochemical properties on the cellular and molecular processes that define SPION interplay with primary neural cells. Particularly, we have designed two different SPION structures, NFA (i.e., a denser multicore structure accompanied by a slightly less negative surface charge and a higher magnetic response) and NFD (i.e., a larger surface area and more negatively charged), and identified specific biological responses dependent on SPION type, concentration, exposure time, and magnetic actuation. Interestingly, NFA SPIONs display a higher cell uptake, likely driven by their less negative surface and smaller protein corona, more significantly impacting cell viability and complexity. The tight contact of both SPIONs with neural cell membranes results in the significant augmentation of phosphatidylcholine, phosphatidylserine, and sphingomyelin and the reduction of free fatty acids and triacylglycerides for both SPIONs. Nonetheless, NFD induces greater effects on lipids, especially under magnetic actuation, likely indicating a preferential membranal location and/or a tighter interaction with membrane lipids than NFA, in agreement with their lower cell uptake. From a functional perspective, these lipid changes correlate with an increase in plasma membrane fluidity, again larger for more negatively charged nanoparticles (NFD). Finally, the mRNA expression of iron-related genes such as Ireb-2 and Fth-1 remains unaltered, while TfR-1 is only detected in SPION-treated cells. Taken together, these results demonstrate the substantial impact that minor physicochemical differences of nanomaterials may exert in the specific targeting of cellular and molecular processes. A denser multicore structure generated by autoclave-based production is accompanied by a slight difference in surface charge and magnetic properties that become decisive for the biological impact of these SPIONs. Their capacity to markedly modify the lipidic cell content makes them attractive as lipid-targetable nanomedicines.

Multicore-based ferrofluids in zero field: initial magnetic susceptibility and self-assembly mechanisms.

The necessity to improve magnetic building blocks in magnetic nano-structured soft materials stems from a fascinating potential these materials have in bio-medical applications and nanofluidics. Along with practical reasons, the interplay of magnetic and steric interactions on one hand, and entropy, on the other, makes magnetic soft matter fundamentally challenging. Recently, in order to tailor magnetic response of the magnetic particle suspensions, the idea arose to replace standard single-core nanoparticles with nano-sized clusters of single-domain nanoparticles (grains) rigidly bound together by solid polymer matrix - multicore magnetic nanoparticles (MMNPs). To pursue this idea, a profound understanding of the MMNP interactions and self-assembly is required. In this work we present a computational study of the MMNP suspensions and elucidate their self-assembly and magnetic susceptibility. We show that depending on the magnetic moment of individual grains the suspensions exhibit qualitatively distinct regimes. Firstly, if the grains are moderately interacting, they contribute to a significant decrease of the remanent magnetisation of MMNPs and as such to a decrease of the magnetic susceptibility, this way confirming previous findings. If the grains are strongly interacting, instead, they serve as anchor points and support formation of grain clusters that span through several MMNPs, leading to MMNP cluster formation and a drastic increase of the initial magnetic response. Both the topology of the clusters and their size distribution in MMNP suspensions is found to be notably different from those formed in conventional magnetic fluids or magnetorheological suspensions.

Plasmonic/magnetic liposomes based on nanoparticles with multicore-shell architecture for chemo/thermotherapy

Multifunctional nanosystems are capable to carry one or more therapeutic agents (thermal and/or targeting agents and chemotherapeutic drugs), offering the capability to concurrently perform different treatment modalities using a single nanosystem. Cluster nanostructures, consisting of densely packed aggregates of magnetic nanoparticles, have shown enhanced heating capabilities. Their combination with plasmonic nanoparticles enable synergistic behavior between dual hyperthermia (magneto-photothermia), allowing overheating cancer cells while increasing drug toxicity. In this work, multicore magnetic nanoparticles (NPs) of MnFe2O4 were prepared using oxamide and melamine as clustering agents. The multicore NPs prepared with oxamide were covered with a gold shell, resulting in multicore magnetic/plasmonic NPs with an increased SAR of 173.80 W/g, under NIR light. Liposomes based on these magnetic/plasmonic NPs were prepared and the model drug curcumin was loaded in these nanocarriers with a high encapsulation efficiency. The fusion between the curcumin-loaded magnetic/plasmonic liposomes and models of cell membranes (labelled with Nile Red) was confirmed by FRET, pointing the magneto/plasmonic liposomes as promising for dual cancer therapy (combined hyperthermia and chemotherapy).

Design of functionalized magnetic silica multi-core composite nanoparticles for synergistic magnetic hyperthermia/radiotherapy in cancer cells

Nanomaterials in particular the magnetic nanoparticles (MNPs) offer tremendous potential for cancer treatment due to their unique intrinsic properties. Combining materials with a variety of functional groups, and forming a multifunctional nanosystem to overcome the limitations of monotherapy for cancer treatment has always been a research focus with notable difficulties. Considering the many challenges faced by radiotherapy and hyperthermia, in this study, we designed a rational strategy for magnetic hyperthermia using Fe3O4@SiO2@Sec2@FA nanoparticles as a novel nano-radiosensitizer to simultaneously enhance the therapeutic effects of radiotherapy in the future. Fe3O4@SiO2 core–shell structured nanoparticles were synthesized with an appropriate silica layer thickness to maintain good saturation magnetization. The as-prepared Fe3O4@SiO2@Sec2@FA nanoparticles had the specific absorption rate (SAR)value of 57 W/g, which was below the clinically acceptable alternating magnetic field value of 4.9 × 109 Am−1s−1, indicating good heat generation efficiency (the temperature level ΔT=6–10 °C). Moreover, Folate-modified nanoparticles exhibited approximately 6-fold higher cellular internalization of Hela cells with no obvious cytotoxicity for the Hela and MDA-MB-231 cells, and lower cytotoxicity for the HUVECs in a concentration range of 0–150 µg/mL. In addition, these nanoparticles were modified on the silica surface by L-selenocystine, which could enhance the elimination of tumor cells by producing reactive oxygen species under X-rays, resulting in a novel radiosensitization effect. Therefore, the as-prepared Fe3O4@SiO2@Sec2@FA nanoparticles with good biocompatibility and active targeting would possess synergistic magnetic hyperthermia/radiotherapy effect.

Structural and magnetic equilibrium properties of a semi-dilute suspension of magnetic multicore nanoparticles

The idea to create smart magnetically controllable nanostructured materials is highly appealing from both fundamental science point of view and application perspectives. Ample investigations of single-domain magnetic nanoparticles embedded in liquid and gel-like magneto-passive carriers revealed a plethora of new phenomena from controllable equilibrium self-assembly to a designed heat dissipation on the application of AC magnetic fields. However, all the effects in such systems are limited by the physical energy and entropy scales of nanoparticles and are very sensitive to temperature changes and confinement. As a result, among new types of complex magnetic materials, magnetic multicore nanoparticles (MMNPs) made of rigidly bound single-domain nanograins were proposed. The properties of such systems are resulting from inter-grain and grain-field interactions, and are not yet fully understood. In this study, employing Langevin dynamics computer simulations, we analyse the interplay of the aforementioned interactions in a dilute suspension of MMNPs made of grains with negligible magnetic anisotropy. We find that the stronger are the inter-grain interactions the lower is the initial magnetic response of MMNPs. The response is though hindered, rather than suppressed: at a certain intensity of an applied magnetic field a sufficient degree of the alignment of the grain magnetic moments and the field is achieved and a large-scale self-assembly accompanied by a rapid growth of magnetisation is observed. The strength of interactions essential for this crossover is much higher than that for a suspension of single-domain grains with the same concentration and magnetic saturation.

Magnetoliposomes Containing Multicore Nanoparticles and a New Antitumor Thienopyridine Compound with Potential Application in Chemo/Thermotherapy.

Multicore magnetic nanoparticles of manganese ferrite were prepared using carboxymethyl dextran as an agglutinating compound or by an innovative method using melamine as a cross-coupling agent. The nanoparticles prepared using melamine exhibited a flower-shape structure, a saturation magnetization of 6.16 emu/g and good capabilities for magnetic hyperthermia, with a specific absorption rate (SAR) of 0.14 W/g. Magnetoliposome-like structures containing the multicore nanoparticles were prepared, and their bilayer structure was confirmed by FRET (Förster Resonance Energy Transfer) assays. The nanosystems exhibited sizes in the range of 250–400 nm and a low polydispersity index. A new antitumor thienopyridine derivative, 7-[4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl]thieno[3,2-b]pyridine, active against HeLa (cervical carcinoma), MCF-7 (breast adenocarcinoma), NCI-H460 (non-small-cell lung carcinoma) and HepG2 (hepatocellular carcinoma) cell lines, was loaded in these nanocarriers, obtaining a high encapsulation efficiency of 98 ± 2.6%. The results indicate that the new magnetoliposomes can be suitable for dual cancer therapy (combined magnetic hyperthermia and chemotherapy).

Design and Development of Gold-Loaded and Boron-Attached Multicore Manganese Ferrite Nanoparticles as a Potential Agent in Biomedical Applications.

Early diagnosis and effective treatment of cancer are significant issues that should be focused on since it is one of the most deadly diseases. Multifunctional nanomaterials can offer new cancer diagnoses and treatment possibilities. These nanomaterials with diverse functions, including targeting, imaging, and therapy, are being studied extensively in a way that minimize overcoming the limitations associated with traditional cancer diagnosis and treatment. Therefore, the goal of this study is to prepare multifunctional nanocomposites possessing the potential to be used simultaneously in imaging such as magnetic resonance imaging (MRI) and dual cancer therapy such as photothermal therapy (PTT) and boron neutron capture therapy (BNCT). In this context, multi-core MnFe2O4 nanoparticles, which can be used as a potential MRI contrast agent and target the desired region in the body via a magnetic field, were successfully synthesized via the solvothermal method. Then, multi-core nanoparticles were coated with polydopamine (PDA) to reduce gold nanoparticles, bind boron on the surface, and ensure the biocompatibility of all materials. Finally, gold nanoparticles were reduced on the surface of PDA-coated MnFe2O4, and boric acid was attached to the hybrid materials for also possessing the ability to be used as a potential agent in PTT and BNCT applications in addition to being an MRI agent. According to the cell viability assay, treatment of the glioblastoma cell line (T98G) with MnFe2O4@PDA-Au-BA for 24 and 48 h did not cause any significant cell death, indicating good biocompatibility. All analysis results showed that the developed MnFe2O4@PDA-Au-BA multifunctional material could be a helpful candidate for biomedical applications such as MRI, PTT, and BNCT.

Catalytically stable monodispersed multi-core Ni-Co nanoparticles encapsulated with SiO2 shells for dry reforming of CH4 with CO2

Enhanced thermal and catalytic stability of monodispersed Ni-Co bimetal nanoparticles with its even size distribution of ~6 nm encapsulated by SiO2 shell (NC@Si) having multicore-shell structures were verified for a harsh dry reforming of methane with CO2 (DRM). The extents of coke formations and aggregations of Ni-Co nanoparticles were dramatically suppressed with positive contributions of oxophilic Co species as well as by their spatial confinement effects. The optimal N8C2@Si with a Ni/Co molar ratio of ~4 revealed a relatively higher CH4 and CO2 conversion of 74.1% and 83.7% at T = 800 °C without significant deactivation phenomena. The original morphologies of the monodispersed Ni-Co nanoparticles were well preserved even after a long-run DRM reaction for 120 h with an insignificant coke formation and active metal aggregation. The superior catalytic activity and stability of the N8C2@Si and N9C1@Si were attributed to the highly-dispersed oxophilic metallic cobalt oxides in the monodispersed stable Ni-Co nanoparticles, which enhanced CO2 adsorption capacity as well as increased thermal stability of the spatially confined Ni-Co nanoparticles with the help of mesoporous SiO2 shell at its optimal aging time less than 4 h. The new multicore-shell structures of the N8C2@Si can effectively suppress the filamentous coke formations as well as minimize the Ni-Co multicore aggregations by stronger metal-SiO2 interactions in the mesoporous protective SiO2 shells.

Doxorubicin delivery performance of superparamagnetic carbon multi-core shell nanoparticles: pH dependence, stability and kinetic insight

In the past decade, magnetic nanoparticles (MNPs) have been among the most attractive nanomaterials used in different fields, such as environmental and biomedical applications. The possibility of designing nanoparticles with different functionalities allows for advancing the biomedical applications of these materials. Additionally, the magnetic characteristics of the nanoparticles enable the use of magnetic fields to drive the nanoparticles to the desired sites of delivery. In this context, the development of new MNPs in new approaches for drug delivery systems (DDSs) for cancer treatment has increased. However, the synthesis of nanoparticles with high colloidal stability triggered drug delivery, and good biocompatibility remains a challenge. Herein, multi-core shell MNPs functionalized with Pluronic ® F-127 were prepared and thoroughly characterized as drug carriers for doxorubicin delivery. The functionalized nanoparticles have an average size of 17.71 ± 4.2 nm, high water colloidal stability, and superparamagnetic behavior. In addition, the nanoparticles were able to load 936 μg of DOX per mg of functionalized nanomaterial. Drug release studies at different pH values evidenced a pH-triggered DOX release effect. An increase of 62% in cumulative drug release was observed at pH simulating tumor endosome/lysosome microenvironments (pH 4.5) compared to physiological conditions (pH 7.4). In addition, an innovative dynamic drug delivery study was performed as a function of pH. The results from this test confirmed the pH-induced doxorubicin release capability of carbon multi-core shell MNPs. The validity of traditional kinetic models to fit dynamic pH-dependent drug release was also studied for predictive purposes.

Novel Nanoparticle-Based Cancer Treatment, Effectively Inhibits Lung Metastases and Improves Survival in a Murine Breast Cancer Model.

Sarah Nanoparticles (SaNPs) are unique multicore iron oxide-based nanoparticles, developed for the treatment of advanced cancer, following standard care, through the selective delivery of thermal energy to malignant cells upon exposure to an alternating magnetic field. For their therapeutic effect, SaNPs need to accumulate in the tumor. Since the potential accumulation and associated toxicity in normal tissues are an important risk consideration, biodistribution and toxicity were assessed in naïve BALB/c mice. Therapeutic efficacy and the effect on survival were investigated in the 4T1 murine model of metastatic breast cancer. Toxicity evaluation at various timepoints did not reveal any abnormal clinical signs, evidence of alterations in organ function, nor histopathologic adverse target organ toxicity, even after a follow up period of 25 weeks, confirming the safety of SaNP use. The biodistribution evaluation, following SaNP administration, indicated that SaNPs accumulate mainly in the liver and spleen. A comprehensive pharmacokinetics evaluation, demonstrated that the total percentage of SaNPs that accumulated in the blood and vital organs was ~78%, 46%, and 36% after 4, 13, and 25 weeks, respectively, suggesting a time-dependent clearance from the body. Efficacy studies in mice bearing 4T1 metastatic tumors revealed a 49.6% and 70% reduction in the number of lung metastases and their relative size, respectively, in treated vs. control mice, accompanied by a decrease in tumor cell viability in response to treatment. Moreover, SaNP treatment followed by alternating magnetic field exposure significantly improved the survival rate of treated mice compared to the controls. The median survival time was 29 ± 3.8 days in the treated group vs. 21.6 ± 4.9 days in the control, p-value 0.029. These assessments open new avenues for generating SaNPs and alternating magnetic field application as a potential novel therapeutic modality for metastatic cancer patients.

Nanoparticles for Magnetic Heating: When Two (or More) Is Better Than One.

The increasing use of magnetic nanoparticles as heating agents in biomedicine is driven by their proven utility in hyperthermia therapeutic treatments and heat-triggered drug delivery methods. The growing demand of efficient and versatile nanoheaters has prompted the creation of novel types of magnetic nanoparticle systems exploiting the magnetic interaction (exchange or dipolar in nature) between two or more constituent magnetic elements (magnetic phases, primary nanoparticles) to enhance and tune the heating power. This process occurred in parallel with the progress in the methods for the chemical synthesis of nanostructures and in the comprehension of magnetic phenomena at the nanoscale. Therefore, complex magnetic architectures have been realized that we classify as: (a) core/shell nanoparticles; (b) multicore nanoparticles; (c) linear aggregates; (d) hybrid systems; (e) mixed nanoparticle systems. After a general introduction to the magnetic heating phenomenology, we illustrate the different classes of nanoparticle systems and the strategic novelty they represent. We review some of the research works that have significantly contributed to clarify the relationship between the compositional and structural properties, as determined by the synthetic process, the magnetic properties and the heating mechanism.

Reproducibility and Scalability of Magnetic Nanoheater Synthesis.

The application of magnetic nanoparticles requires large amounts of materials of reproducible quality. This work explores the scaled-up synthesis of multi-core iron oxide nanoparticles through the use of thermal decomposition in organic media and kilograms of reagents. To this end, we check the effect of extending the high temperature step from minutes to hours. To address the intrinsic variability of the colloidal crystallization nucleation process, the experiments were repeated and analyzed statistically. Due to the simultaneity of the nuclei growth and agglomeration steps, the nanostructure of the samples produced was a combination of single- and multi-core nanoparticles. The main characteristics of the materials obtained, as well as the reaction yields, were analyzed and compared. As a general rule, yield, particle size, and reproducibility increase when the time at high temperature is prolonged. The samples obtained were ranked in terms of the reproducibility of different structural, colloidal, and magnetic features. The capability of the obtained materials to act as nanoheaters in magnetic hyperthermia was assessed, showing a strong dependence on the crystallite size (calculated by X-ray diffraction), reflecting the nanoparticle volume with a coherent magnetization reversal.

Effective Néel relaxation time constant and intrinsic dipolar magnetism in a multicore magnetic nanoparticle system

The coexisting Néel and Brownian relaxation behaviors of magnetic nanoclusters in a viscous medium lead to a highly nonlinear field-dependent magnetization response, which can benefit magnetic particle imaging and hyperthermia. To empirically correlate the moment and particle dynamics with the core and cluster sizes, we performed spectroscopic susceptometry to assess frequency-dependent complex magnetic susceptibility of water-dispersed magnetic nanoclusters at very low field amplitude. The superparamagnetic core particles of nanoclusters should undergo fast moment dynamics. However, for the nanoclusters experiencing the field-driven Brownian relaxation, their constituent core particles appear to collectively behave as a large effective core with a long Néel relaxation time constant. We later numerically interpolated the phase-delay spectra of the immobilized nanoclusters to estimate the Néel relaxation time constant attributed to the intrinsic dipolar interparticle magnetism. From additional static magnetometry, the overlapping bimodal magnetic moment distribution predicts the secondary core sizes larger than the actual sizes from the electron microscopy images. The different estimates of the effective Néel relaxation time constant obtained from the (nearly field-free) frequency-dependent and (static) field-dependent magnetization responses further indicate the activation energies limiting the relaxation behavior of magnetic nanoclusters. This finding highlights the number of effective cores affecting the intracluster interaction energy.