Highly porous, water-soluble, superparamagnetic, and biocompatible magnetite nanocrystal clusters for targeted drug delivery

Iron oxide magnetic aggregates: Aspects of synthesis, computational approaches and applications

Superparamagnetic magnetite nanoparticles have been central to numerous investigations in the past few decades for their use in many applications, such as drug delivery, medical diagnostics, magnetic separation, and material science. However, the properties of single magnetic nanoparticles are sometimes not sufficient to accomplish tasks where a strong magnetic response is required. In light of this, aggregated magnetite nanoparticles have been proposed as an alternative advanced material, which may expand and combine some of the advantages of single magnetic nanoparticles, including superparamagnetism, with an enhanced magnetic moment and increased colloidal stability. This review comprehensively discusses the current literature on aggregates made of magnetic iron oxide nanoparticles. This review is divided into three sections. First, the current synthetic strategies for magnetite nanoparticle aggregates are discussed, together with the influence of different stabilizers on the primary crystals and the final aggregate size and morphology. The second section is dedicated to computational approaches, such as density functional methods (which permit accurate predictions of electronic and magnetic properties and shed light on the behavior of surfactant molecules on iron oxide surfaces) and molecular dynamics simulations (which provide additional insight into the influence of ligands on the surface chemistry of iron oxide nanocrystals). The last section discusses current and possible future applications of iron oxide magnetic aggregates, including wastewater treatment, water purification, medical applications, and magnetic aggregates for materials displaying structural colors.

Material-engineered bioartificial microorganisms enabling efficient scavenging of waterborne viruses

Material-based tactics have attracted extensive attention in driving the functional evolution of organisms. In aiming to design steerable bioartificial organisms to scavenge pathogenic waterborne viruses, we engineer Paramecium caudatum (Para), single-celled microorganisms, with a semiartificial and specific virus-scavenging organelle (VSO). Fe3O4 magnetic nanoparticles modified with a virus-capture antibody (MNPs@Ab) are integrated into the vacuoles of Para during feeding to produce VSOs, which persist inside Para without impairing their swimming ability. Compared with natural Para, which has no capture specificity and shows inefficient inactivation, the VSO-engineered Para (E-Para) specifically gathers waterborne viruses and confines them inside the VSOs, where the captured viruses are completely deactivated because the peroxidase-like nano-Fe3O4 produces virus-killing hydroxyl radicals (•OH) within acidic environment of VSO. After treatment, magnetized E-Para is readily recycled and reused, avoiding further contamination. Materials-based artificial organelles convert natural Para into a living virus scavenger, facilitating waterborne virus clearance without extra energy consumption.

Nanoparticles-induced potential toxicity on human health: Applications, toxicity mechanisms, and evaluation models

Nanoparticles (NPs) have become one of the most popular objects of scientific study during the past decades. However, despite wealth of study reports, still there is a gap, particularly in health toxicology studies, underlying mechanisms, and related evaluation models to deeply understanding the NPs risk effects. In this review, we first present a comprehensive landscape of the applications of NPs on health, especially addressing the role of NPs in medical diagnosis, therapy. Then, the toxicity of NPs on health systems is introduced. We describe in detail the effects of NPs on various systems, including respiratory, nervous, endocrine, immune, and reproductive systems, and the carcinogenicity of NPs. Furthermore, we unravels the underlying mechanisms of NPs including ROS accumulation, mitochondrial damage, inflammatory reaction, apoptosis, DNA damage, cell cycle, and epigenetic regulation. In addition, the classical study models such as cell lines and mice and the emerging models such as 3D organoids used for evaluating the toxicity or scientific study are both introduced. Overall, this review presents a critical summary and evaluation of the state of understanding of NPs, giving readers more better understanding of the NPs toxicology to remedy key gaps in knowledge and techniques.

Nanocluster-Based Drug Delivery and Theranostic Systems: Towards Cancer Therapy

Over the last decades, the global life expectancy of the population has increased, and so, consequently, has the risk of cancer development. Despite the improvement in cancer therapies (e.g., drug delivery systems (DDS) and theranostics), in many cases recurrence continues to be a challenging issue. In this matter, the development of nanotechnology has led to an array of possibilities for cancer treatment. One of the most promising therapies focuses on the assembly of hierarchical structures in the form of nanoclusters, as this approach involves preparing individual building blocks while avoiding handling toxic chemicals in the presence of biomolecules. This review aims at presenting an overview of the major advances made in developing nanoclusters based on polymeric nanoparticles (PNPs) and/or inorganic NPs. The preparation methods and the features of the NPs used in the construction of the nanoclusters were described. Afterwards, the design, fabrication and properties of the two main classes of nanoclusters, namely noble-metal nanoclusters and hybrid (i.e., hetero) nanoclusters and their mode of action in cancer therapy, were summarized.

PEG size effect and its interaction with Fe3O4 nanoparticles synthesized by solvothermal method: morphology and effect of pH on the stability

The synthesis and characterization of Fe3O4 magnetic nanoparticles (MNPs) obtained by the solvothermal method in ethyleneglycol with the addition of polyethyleneglycol (PEG) with molar mass of 4000, 8000 and 20000 g mol−1 are described, aimed at evaluating its effect on the size, morphology and stability of the nanoparticle. The syntheses were carried out by solubilizing the precursors at 85 and 140 °C, providing smaller nanoparticles as well as smaller crystallites at higher temperatures, while the effect of PEG was less evident. Measurements of nanoparticle surface areas synthesized with PEG 4000 and 20000 g mol−1 at 140 °C provided values of 76 and 14 m2 g−1, respectively, indicating that PEG 4000 surrounds the crystallites, while PEG 20000 preferably surrounds the whole MNP. As a consequence, MNP with very dissimilar porosities were obtained. Electron energy loss spectroscopy (EELS) indicated that MNP synthesized with PEG 20000 possesses higher electronic density than those obtained with PEG 4000, in agreement with the surface area results. Infrared spectroscopy and thermogravimetric analysis demonstrated the presence of PEG in the particles, whose amount increased as the particle size decreased. Dynamic Light Scattering (DLS) measurements showed that MNP hydrodynamic radius increases with the PEG size and stability in solution increases from pH 5.0 to 9.0 for smaller NP, while polymer presents slight effect on stability for the larger particles. The results obtained in this work show that properties of MNP can be tuned by the dissolution temperature of the chemical precursors and the PEG molar mass, changing their porosity and stability in solution, that are important variables in processes of adsorption, drug delivery and sensor developing.

Oxygen Vacancy Defect-Induced Activity Enhancement of Gd Doping Magnetic Nanocluster for Oxygen Supplying Cancer Theranostics

This work finds that Fe₃O₄ nanoclusters can rearrange by Gd doping and then self-assemble to a hollow magnetic nanocluster (HMNC), providing larger magnetic moments to obtain an excellent MRI capability and increasing the number of oxygen vacancies in HMNC. The hollow structure makes platinum(IV) prodrugs effectively load into HMNC. Second, plenty of oxygen vacancy defects can capture oxygen molecules, enhance the catalytic activity of HMNC, and then promote intracellular ROS generation. On the basis of this, a targeting iRGD-labeled HMNC nanosystem (iHMNCPt-O₂) is developed through loading oxygen molecules and platinum(IV) prodrugs for chemo- and chemodynamic therapy of cancer. This nanosystem shows an excellent response ability to weak acid and GSH, which can cause a series of cascade reactions in a cell. These cascade reactions are dramatically enhanced at the intracellular ROS level, cause mitochondria and DNA damage, and then induce cancer cell death. Besides, systemic delivery of iHMNCPt-O₂ significantly enhanced the MRI contrast signal of tumors and improved the quality of MR images, accurately diagnosing tumors. Therefore, this work provides a novel method for accelerating the Fenton-like reaction and enhancing the MRI capability and fabricates a promising "all-in-one" system to overwhelm the problems of cancer theranostic.

Preparation and Application of Iron Oxide Nanoclusters

Magnetic iron oxide nanoclusters, which refers to a group of individual nanoparticles, have recently attracted much attention because of their distinctive behaviors compared to individual nanoparticles. In this review, we discuss preparation methods for creating iron oxide nanoclusters, focusing on synthetic procedures, formation mechanisms, and the quality of the products. Then, we discuss the emerging applications for iron oxide nanoclusters in various fields, covering traditional and novel applications in magnetic separation, bioimaging, drug delivery, and magnetically responsive photonic crystals.

Large-scale preparation of size-controlled Fe3O4@SiO2 particles for electrophoretic display with non-iridescent structural colors

Monodisperse colloidal particles have promising applications in electrophoretic displays with vivid colors, reversibility and low switching times. In this study, a facile, effective and large-scale strategy for preparing size-controlled Fe₃O₄@SiO₂ particles is reported. Multiple Fe₃O₄ particles were synthesized by a modified solvothermal method using sodium citrate as a surface modifier with a binary solvent, and were then coated with a SiO₂ layer to obtain a highly negatively charged surface via a modified Stöber method. Owing to the easily controlled sizes and sufficient surface charges, Fe₃O₄@SiO₂ particles can be assembled into colloidal amorphous arrays with the balance of electrostatic repulsion and electrophoretic forces. The reflections cover wavelengths ranging from 802 to 453 nm, and were optimized by investigating the dependence of the particles on variables such as particle size, particle volume fraction, and electric field intensity. The large-scale preparation of electrically responsive Fe₃O₄@SiO₂ particles facilitates an electrophoretic display with broad-range colors, showing the practical potential in industrial application.

Fe₃O₄@SiO₂ particles were prepared on the gram-scale by selecting Na₃Cit as the modifier with binary solvent and were assembled into colloidal amorphous arrays with unique and attractive optical properties for EPD.

Synthesis of Iron Oxide Nanoclusters by Thermal Decomposition

Herein, we report a novel one-step solvothermal synthesis of magnetite nanoclusters (MNCs). In this report, we discuss the synthesis, structure, and properties of MNCs and contrast enhancement in T₂-weighted MR images using magnetite nanoclusters. The effect of different organic acids, used as surfactants, on the size and shape of MNCs was investigated. The structure and properties of samples were determined by magnetic measurements, TGA, TEM, HRTEM, XRD, FTIR, and MRI. Magnetic measurements show that obtained MNCs have relatively high saturation magnetization values (65.1-81.5 emu/g) and dependence of the coercive force on the average size of MNCs was established. MNCs were transferred into an aqueous medium by Pluronic F-127, and T₂-relaxivity values were determined. T₂-Weighted MR phantom images clearly demonstrated that such magnetite nanoclusters can be used as contrast agents for MRI.

Hydrophilic and positively charged polyethylenimine-functionalized mesoporous magnetic clusters for highly efficient removal of Pb(II) and Cr(VI) from wastewater

We develop mesoporous magnetic clusters (MMCs) functionalized with hydrophilic branched polyethylenimine (b-PEI), later called b-MG, and MMCs functionalized with positively charged b-PEI (p-MG). These materials efficiently remove Pb(II) and Cr(VI) from wastewater. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and nitrogen adsorption-desorption analysis results clearly indicate that hydrophilic b-PEI and positively charged b-PEI are successfully attached to the MMC surfaces. Wide-angle X-ray diffraction, high-resolution transmission electron microscopy, and field-emission scanning electron microscopy analyses confirm that the crystal structures and morphologies of the MMCs are maintained well even when wet chemical modification processes are used to introduce hydrophilic b-PEI and positively charged b-PEI to the MMC surfaces. Langmuir and Sips isotherm models are applied to describe Pb(II) adsorption behavior of the b-MG and Cr(VI) adsorption behavior of the p-MG. The isotherm models indicate that the maximum adsorption capacities of b-MG and p-MG, respectively, are 216.3 and 334.1 mg g^-1, respectively. These are higher than have previously been found for other adsorbents. In reusability tests, using magnetic separation and controlling the pH, the Pb(II) recovery efficiency of the b-MG is 95.6% and the Cr(VI) recovery efficiency of the p-MG is 68.0% even after the third cycle.

One-pot synthesis of multi-functional magnetite–polysilsesquioxane hybrid nanoparticles for the selective Fe3+ and some heavy metal ions adsorption

Multi-functional magnetite–polysilsesquioxane (PSSQ) hybrid nanoparticles were synthesised in a one-pot approach using ferrous and ferric chlorides and various silane monomers by coprecipitation followed by a surface grafting method.

Controlled synthesis of water-dispersible and superparamagnetic Fe3O4 nanomaterials by a microwave-assisted solvothermal method: from nanocrystals to nanoclusters

Highly tunable Fe₃O₄ nanocrystals and nanoclusters with water-dispersible and superparamagnetic properties were successfully synthesized by a facile and effective microwave-assisted solvothermal method.

Gram-scale synthesis of superparamagnetic Fe3O4 nanocrystal clusters with long-term charge stability for highly stable magnetically responsive photonic crystals

We report the gram-scale hydrothermal synthesis of superparamagnetic Fe₃O₄ CNCs with superior long-term charge stability, which are suitable building blocks for magnetically responsive photonic crystals (MRPCs) with widely, rapidly and reversibly tunable diffractions across the visible and near IR range, as well as long-term stability of photonic performances. The scalable synthesis of Fe₃O₄ CNCs with excellent long-term colloidal stability will facilitate their wide application in photonics, biomedicine, catalysis and other areas.

Transcatheter intra-arterial infusion of doxorubicin loaded porous magnetic nano-clusters with iodinated oil for the treatment of liver cancer

A promising strategy for liver cancer treatment is to deliver chemotherapeutic agents with multifunctional carriers into the tumor tissue via intra-arterial (IA) transcatheter infusion. These carriers should release drugs within the target tissue for prolonged periods and permit intra-procedural multi-modal imaging of selective tumor delivery. This targeted transcatheter delivery approach is enabled via the arterial blood supply to liver tumors and utilized in current clinical practice which is called chemoembolization or radioembolization. During our study, we developed Doxorubicin (Dox) loaded porous magnetic nano-clusters (Dox-pMNCs). The porous structure and carboxylic groups on the MNCs achieved high-drug loading efficiency and sustained drug release, along with magnetic properties resulting in high MRI T2-weighted image contrast. Dox-pMNC within iodinated oil, Dox-pMNCs, and Dox within iodinated oil were infused via hepatic arteries to target liver tumors in a rabbit model. MRI and histological evaluations revealed that the long-term drug release and retention of Dox-pMNCs within iodinated oil induced significantly enhanced liver cancer cell death.

Facile synthesis of superparamagnetic magnetite nanoflowers and their applications in cellular imaging

Thermal decomposition of an iron-oleate complex in the presence of a surfactant gives water-soluble biocompatible superparamagnetic magnetite nanoflowers via a one-pot reaction.

Controllable synthesis of graphene nanoscroll-wrapped Fe3O4 nanoparticles and their lithium-ion battery performance

The mass ratio of Fe₃O₄/GO plays an important role in determining the structure and the electrochemical performance of Fe₃O₄@GNS.

Facile preparation of one-dimensional wrapping structure: graphene nanoscroll-wrapped of Fe3O4 nanoparticles and its application for lithium-ion battery

Graphene nanoscroll (GNS) is a spirally wrapped two-dimensional (2D) graphene sheet (GS) with a 1D tubular structure resembling that of a multiwalled carbon nanotube (MWCNT). GNS provide open structure at both ends and interlayer galleries that can be easily intercalated and adjusted, which show great potential applications in energy storage. Here we demonstrate a novel and simple strategy for the large-scale preparation of GNSs wrapping Fe3O4 nanoparticles (denoted as Fe3O4@GNSs) from graphene oxide (GO) sheets by cold quenching in liquid nitrogen. When a heated aqueous mixed suspension of GO sheets and Fe3O4 nanoparticles is immersed in liquid nitrogen, the in-situ wrapping of Fe3O4 nanoparticles with GNSs is easily realized. The structural conversion is closely correlated with the initial temperature of mixed suspension, the zeta potential of Fe3O4 nanoparticles and the immersion way. Remarkably, such hybrid structure provides the right combination of electrode properties for high-performance lithium-ion batteries. Compared with other wrapping structure, such 1D wrapping structure (GNSs wrapping) effectively limits the volume expansion of Fe3O4 nanoparticles during the cycling process, consequently, a high reversible capacity, good rate capability, and excellent cyclic stability are achieved with the material as anode for lithium storage. The results presented here may pave a way for the large-scale preparation of GNS-based materials in electrochemical energy storage applications.

Assembly-mediated interplay of dipolar interactions and surface spin disorder in colloidal maghemite nanoclusters

Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of ∼13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the increasing volume fraction, φ, of the inorganic magnetic phase that goes from individual colloidal nanoparticles (φ = 0.47) to clusters (φ = 0.72). The frozen-liquid dispersions of the latter exhibit weak ferrimagnetic behaviour at 300 K. Comparative Mössbauer spectroscopic studies imply that intra-cluster interactions come into play. New insight emerges from the clusters' temperature-dependent ac susceptibility that displays two maxima in χ''(T), with strong frequency dispersion. Scaling-law analysis together with the observed memory effects suggests that a superspin-glass state settles-in at TB ∼ 160-200 K, while at lower-temperatures, surface spin-glass freezing is established at Tf ∼ 40-70 K. In such nanoparticle-assembled systems, with increased φ, Monte Carlo simulations corroborate the role of the inter-particle dipolar interactions and that of the constituent nanoparticles' surface spin disorder in the emerging spin-glass dynamics.

Colloidal assemblies of oriented maghemite nanocrystals and their NMR relaxometric properties

¹H-NMR relaxometric experiments over an extended frequency range show that ferrimagnetic colloidal nanoclusters exhibit enhanced transverse relaxivity, r₂.

Magnetic colloidal supraparticles: design, fabrication and biomedical applications

Magnetic nanoparticles (MNPs) bear many intriguing properties such as superparamagnetism, high specific surface area, remarkable colloidal stability and biocompatibility, which evoke great interest and desire of exploration in biomedical applications. For the use in the complicated physiological environment, MNPs are still being developed to have the enhanced performances and down-to-earth practicality. Engineering of MNPs into hierarchical structures is thus proposed to create a new family of magnetic materials, magnetic colloidal supraparticles (MCSPs), which exhibit collective properties and unique nanomaterial characters. From a biomedical point of view, applicability of MCSPs is somewhat more distinctive in contrast to their primary MNPs, because MCSPs are amenable to modulation of secondary structure, promotion of magnetic responsiveness and ease of function design. As a result, MCSPs have been subject to intense researches in recent years, with the aim to develop outstanding composite materials for biomedical applications. In this review, we embark on an overview of foundational topics that detail the design and fabrication of MCSPs by evaporation-induced emulsion and solvothermal techniques, and continue with a guideline for modification of MCSPs with inorganic oxides and organic polymers. Particular focus is then placed on the biomedical applications of modified MCSPs. Many examples illustrate the latest progress in design of MCSP-based microspheres for magnetic resonance imaging, targeted drug delivery, sensing, and harvesting of peptides/proteins. After these detailed accounts, the current challenges and future development of researches and applications are discussed as a conclusion to the review.

Single cell detection using a magnetic zigzag nanowire biosensor

A magnetic zigzag nanowire device was designed for single cell biosensing. Nanowires with widths of 150, 300, 500, and 800 nm were fabricated on silicon trenches by electron beam lithography, electron beam evaporation, and lift-off processes. Magnetoresistance measurements were performed before and after the attachment of a single magnetic cell to the nanowires to characterize the magnetic signal change due to the influence of the magnetic cell. Magnetoresistance responses were measured in different magnetic field directions, and the results showed that this nanowire device can be used for multi-directional detection. It was observed that the highest switching field variation occurred in a 150 nm wide nanowire when the field was perpendicular to the substrate plane. On the other hand, the highest magnetoresistance ratio variation occurred in a 800 nm wide nanowire also when the field was perpendicular to the substrate plane. Besides, the trench-structured substrate proposed in this study can fix the magnetic cell to the sensor in a fluid environment, and the stray field generated by the corners of the magnetic zigzag nanowires has the function of actively attracting the magnetic cells for detection.

One-step solvothermal synthesis of highly water-soluble, negatively charged superparamagnetic Fe3O4 colloidal nanocrystal clusters

Highly charged hydrophilic superparamagnetic Fe3O4 colloidal nanocrystal clusters with an average diameter of 195 nm have been successfully synthesized using a modified one-step solvothermal method. Anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt containing both sulfonate and carboxylate groups was used as the stabilizer. The clusters synthesized under different experimental conditions were characterized with transmission electron microscopy and dynamic light scattering; it was found that the size distribution and water dispersity were significantly affected by the concentration of the polyelectrolyte stabilizer and iron sources in the reaction mixtures. A possible mechanism involving novel gel-like large molecular networks that confined the nucleation and aggregation process was proposed and discussed. The colloidal nanocrystal clusters remained negatively charged in the experimental pH ranges from 2 to 11, and also showed high colloidal stability in phosphate buffered saline (PBS) and ethanol. These highly colloidal stable superparamagnetic Fe3O4 clusters could find potential applications in bioseparation, targeted drug delivery, and photonics.

Magnetoliposomes and their potential in the intelligent drug-delivery field

Research advancements for magnetically guided drug delivery encompass not only the improvement of the design, synthesis and evaluation of more selective nanomaterials bearing magnetic properties, but also the optimization of the transport and delivery of magnetic agents. Such versatile platforms can be utilized for simultaneously carrying therapeutics and diagnostics.

Memory-effects of magnetic nanocomposites

The thermally induced shape memory effect (SME) is the capability of a material to fix a temporary (deformed) shape and recover a 'memorized' permanent shape in response to heat. SMEs in polymers have enabled a variety of applications including deployable space structures, biomedical devices, adaptive optical devices, smart dry adhesives and fasteners. By the incorporation of magnetic nanoparticles (mNP) into shape-memory polymer (SMP), a magnetically controlled SME has been realized. Magnetic actuation of nanocomposites enables remotely controlled devices based on SMP, which might be useful in medical technology, e.g. remotely controlled catheters or drug delivery systems. Here, an overview of the recent advances in the field of magnetic actuation of SMP is presented. Special emphasis is given on the magnetically controlled recovery of SMP with one switching temperature T(sw) (dual-shape effect) or with two T(sw)s (triple-shape effect). The use of magnetic field to change the apparent switching temperature (T(sw,app)) of the dual or triple-shape nanocomposites is described. Finally, the capability of magnetic nanocomposites to remember the magnetic field strength (H) initially used to deform the sample (magnetic-memory effect) is addressed. The distinguished advantages of magnetic heating over conventional heating methods make these multifunctional nanocomposites attractive candidates for in vivo applications.

Glucocorticoid-loaded core-cross-linked polymeric micelles with tailorable release kinetics for targeted therapy of rheumatoid arthritis

Polymerizable and hydrolytically cleavable dexamethasone (DEX, red dot in picture) derivatives were covalently entrapped in core-cross-linked polymeric micelles that were prepared from a thermosensitive block copolymer (yellow and gray building block). By varying the oxidation degree of the thioether in the drug linker, the release rate of DEX could be controlled. The DEX-loaded micelles were used for efficient treatment of inflammatory arthritis in two animal models.