Synthesis of magnetic cobalt ferrite nanoparticles with controlled morphology, monodispersity and composition: the influence of solvent, surfactant, reductant and synthetic conditions

Low-cost one-pot synthesis of hydrophobic and hydrophilic monodispersed iron oxide nanoparticles

The synthesis of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) with size and shape tunability, which is also industrially scalable, remains challenging. Surface functionalization of the nanoparticles is yet another active research subject. Although a variety of inorganic and organometallic precursors have been tried, which are demanding in terms of both cost and effort, the use of iron hydroxide, a simple and cheap iron precursor, has not been explored in detail for the synthesis of SPIONs following a thermal decomposition route. Here, we outline a simple one-pot thermal decomposition route that avoids separate precursor preparation and purification steps and, consequently, is easily scalable. The method involves the alcoholic hydrolysis of a simple iron salt into iron hydroxide, which, on addition of oleic acid, forms the precursor oleate complex in situ, which is subsequently thermally decomposed to produce monodispersed SPIONS. Minor modifications allow for particle dimensions (5-20 nm) and morphology (spheroid or cuboid) to be controlled. Additionally, we explored a simple ligand exchange process for rendering the hydrophobic nanoparticles hydrophilic. Trisodium nitrilotriacetate (NTA), a readily available polycarboxylate, can efficiently transfer the oleate-coated SPIONs to water without the need for separation from the crude reaction mixture. X-ray Rietveld refinement showed that particles obtained by this method had both the magnetite and wustite phases of iron oxide present. Magnetic measurements confirm that the iron oxide particles are superparamagnetic at room temperature, with typical blocking temperatures of 183 K for the spherical and 212 K for the cuboid ones.

High-density polyethylene composites filled with micro- and nano-particles of nickel ferrite: magnetic, mechanical, and thermal properties

With the increasing demand of new magnetic materials for modern technological application alternatives to conventional magnetic materials, the development of lightweight polymer magnetic composites has become a prominent research area. For this perspective, a new magnetic material was developed using 30 wt% nickel ferrite micro and nanoparticles as fillers for a high-density polyethylene matrix. The development process began with the synthesis of NF-micro and NF-nanoparticles using solid-state and co-precipitation techniques, respectively, followed by extrusion molding and injection molding. The success of the synthesis process and the purity of the spinel structure phase were confirmed. Additionally, using the extrusion process produced polymer magnetic composite materials with a good distribution of magnetic particles within the polymer matrix, resulting in good magnetic properties and enhanced mechanical properties of the polymer magnetic materials.

Comparative analysis of cobalt ferrite and iron oxide nanoparticles using bimodal hyperthermia, along with physical and in silico interaction with human hemoglobin

Magnetic nanoparticles (MNPs) have captivated the scientific community towards biomedical applications owing to their numerous distinctive physio-chemical properties. In this work, cobalt ferrite (CFNPs) and iron oxide nanoparticles (IONPs) were synthesized using the thermal decomposition method and then functionalized with polyacrylic acid (PAA) for aqueous dispersion. Associated techniques, namely TEM, FESEM, DLS, XRD, and VSM, were used to characterize the synthesized nanoparticles. We also investigated the light-induced and magnetic-field-induced hyperthermia properties of the PAA-functionalized MNPs. It was found that the PAA-CFNPs show a high specific absorption rate (SAR) compared with the PAA-IONPs. Since blood plasma is essential for the delivery and targeting of drugs, studying biological interactions is crucial for effective therapeutic use. Therefore, we performed physical and in silico studies to probe into the mechanistic interaction of CFNPs and IONPs with human hemoglobin. From these studies, we inferred the successful binding between the nanoparticles and protein. Preliminary in vitro cytocompatibility and photothermal toxicity studies in breast cancer (MCF-7) cells treated with the nanoparticles revealed a low dark toxicity and significant laser-induced photothermal toxicity.

Nanomedicine and nanobiotechnology applications of magnetoelectric nanoparticles

Unlike any other nanoparticles known to date, magnetoelectric nanoparticles (MENPs) can generate relatively strong electric fields locally via the application of magnetic fields and, vice versa, have their magnetization change in response to an electric field from the microenvironment. Hence, MENPs can serve as a wireless two-way interface between man-made devices and physiological systems at the molecular level. With the recent development of room-temperature biocompatible MENPs, a number of novel potential medical applications have emerged. These applications include wireless brain stimulation and mapping/recording of neural activity in real-time, targeted delivery across the blood-brain barrier (BBB), tissue regeneration, high-specificity cancer cures, molecular-level rapid diagnostics, and others. Several independent in vivo studies, using mice and nonhuman primates models, demonstrated the capability to deliver MENPs in the brain across the BBB via intravenous injection or, alternatively, bypassing the BBB via intranasal inhalation of the nanoparticles. Wireless deep brain stimulation with MENPs was demonstrated both in vitro and in vivo in different rodents models by several independent groups. High-specificity cancer treatment methods as well as tissue regeneration approaches with MENPs were proposed and demonstrated in in vitro models. A number of in vitro and in vivo studies were dedicated to understand the underlying mechanisms of MENPs-based high-specificity targeted drug delivery via application of d.c. and a.c. magnetic fields. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Synthesis and Functional Characterization of CoxFe3-xO4-BaTiO3 Magnetoelectric Nanocomposites for Biomedical Applications

Nowadays, magnetoelectric nanomaterials are on their way to finding wide applications in biomedicine for various cancer and neurological disease treatment, which is mainly restricted by their relatively high toxicity and complex synthesis. This study for the first time reports novel magnetoelectric nanocomposites of Co_xFe_3-xO₄-BaTiO₃ series with tuned magnetic phase structures, which were synthesized via a two-step chemical approach in polyol media. The magnetic Co_xFe_3-xO₄ phases with x = 0.0, 0.5, and 1.0 were obtained by thermal decomposition in triethylene glycol media. The magnetoelectric nanocomposites were synthesized by the decomposition of barium titanate precursors in the presence of a magnetic phase under solvothermal conditions and subsequent annealing at 700 °C. X-ray diffraction revealed the presence of both spinel and perovskite phases after annealing with average crystallite sizes in the range of 9.0-14.5 nm. Transmission electron microscopy data showed two-phase composite nanostructures consisting of ferrites and barium titanate. The presence of interfacial connections between magnetic and ferroelectric phases was confirmed by high-resolution transmission electron microscopy. Magnetization data showed expected ferrimagnetic behavior and σ_s decrease after the nanocomposite formation. Magnetoelectric coefficient measurements after the annealing showed non-linear change with a maximum of 89 mV/cm*Oe with x = 0.5, 74 mV/cm*Oe with x = 0, and a minimum of 50 mV/cm*Oe with x = 0.0 core composition, that corresponds with the coercive force of the nanocomposites: 240 Oe, 89 Oe and 36 Oe, respectively. The obtained nanocomposites show low toxicity in the whole studied concentration range of 25-400 μg/mL on CT-26 cancer cells. The synthesized nanocomposites show low cytotoxicity and high magnetoelectric effects, therefore they can find wide applications in biomedicine.

Influence of Y3+ and La3+ ions on the structural, magnetic, electrical, and optical properties of cobalt ferrite nanoparticles

In the current study, nanocrystalline CoY_0.5xLa_0.5xFe_2-xO₄ (where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) ferrites have been synthesized via a sol-gel auto combustion process. The synthesized powders were pressed into pellet forms and sintered at 900 °C for 4 h in the air. X-ray diffractometry (XRD) confirmed the single-phase cubic spinel structure of the synthesized samples having the mean crystallite domain sizes ranging from 122 and 54 nm. FTIR spectroscopic analyses revealed two strong bands within the range of 600 to 350 cm^-1, further confirming the cubic inverse spinel structure of the prepared materials. The surface morphologies and composition were investigated by Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) Spectroscopy. The magnetic hysteresis curves recorded at room temperature exhibit ferrimagnetic behavior. The highest coercivity (Hc∼1276 Oe) was found at a high doping (x = 0.10) concentration of Y³⁺ and La³⁺ in cobalt ferrite. Dielectric constant increase with increased doping concentration whereas real-impedance and dielectric loss decrease with increased in doping concentration and applied frequency. The band gap energy increased from 1.48 to 1.53 eV with increasing Y³⁺ and La³⁺concentrations in the UV-Vis region. The elevated levels of magnetic and dielectric substances in the ferrite nanoparticles suggest that the material could be used for magnetic recording media and high-frequency devices.

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.

The role of Co2+cation addition in enhancing the AC heat induction power of (CoxMn1-x)Fe2O4superparamagnetic nanoparticles

The physical role of magnetically semi-hard Co²⁺cation addition in enhancing the AC heat induction temperature (T_AC) or specific loss power (SLP) of solid (Co_xMn_1-x)Fe₂O₄superparamagnetic iron oxide nanoparticles (SPIONPs) was systematically investigated at the biologically safe and physiologically tolerable range ofH_AC(H_AC,safe= 1.12 × 10⁹A m^-1s^-1,f_appl= 100 kHz,H_appl= 140 Oe (11.2 A m^-1)) to demonstrate which physical parameter would be the most critical and dominant in enhancing theT_AC(SLP) of SPIONPs. According to the experimentally and theoretically analyzed results, it was clearly demonstrated that the enhancement of magnetic anisotropy (K_u)-dependent AC magnetic softness including the Néel relaxation time constantτ_N(≈τ_eff, effective relaxation time constant), and its dependent out-of-phase magnetic susceptibilityχ″primarily caused by the Co²⁺cation addition is the most dominant parameter to enhance theT_AC(SLP). This clarified result strongly suggests that the development of new design and synthesis methods enabling to significantly enhance theK_uby improving the crystalline anisotropy, shape anisotropy, stress (magnetoelastic) anisotropy, thermally-induced anisotropy, and exchange anisotropy is the most critical to enhance theT_AC(SLP) of SPIONPs at theH_AC,safe(particularly at the lowerf_appl< 120 kHz) for clinically safe magnetic nanoparticle hyperthermia.

Effect of Oleylamine on the Surface Chemistry, Morphology, Electronic Structure, and Magnetic Properties of Cobalt Ferrite Nanoparticles

The influence of oleylamine (OLA) concentration on the crystallography, morphology, surface chemistry, chemical bonding, and magnetic properties of solvothermal synthesized CoFe₂O₄ (CFO) nanoparticles (NPs) has been thoroughly investigated. Varying OLA concentration (0.01-0.1 M) resulted in the formation of cubic spinel-structured CoFe₂O₄ NPs in the size-range of 20-14 (±1) nm. The Fourier transform spectroscopic analyses performed confirmed the OLA binding to the CFO NPs. The thermogravimetric measurements revealed monolayer and multilayer coating of OLA on CFO NPs, which were further supported by the small-angle X-ray scattering measurements. The magnetic measurements indicated that the maximum saturation (M_S) and remanent (M_r) magnetization decreased with increasing OLA concentration. The ratio of maximum dipolar field (H_dip), coercivity (H_C), and exchanged bias field (H_ex) (at 10 K) to the average crystallite size (D_xrd), i.e., (H_dip/D_xrd), (H_C/D_xrd), and (H_ex/D_xrd), increased linearly with OLA concentration, indicating that OLA concurrently controls the particle size and interparticle interaction among the CFO NPs. The results and analyses demonstrate that the OLA-mediated synthesis allowed for modification of the structural and magnetic properties of CFO NPs, which could readily find potential application in electronics and biomedicine.

Oleic acid/oleylamine ligand pair: a versatile combination in the synthesis of colloidal nanoparticles

A variety of colloidal chemical approaches has been developed in the last few decades for the controlled synthesis of nanostructured materials in either water or organic solvents. Besides the precursors, the solvents, reducing agents, and the choice of surfactants are crucial for tuning the composition, morphology and other properties of the resulting nanoparticles. The ligands employed include thiols, amines, carboxylic acids, phosphines and phosphine oxides. Generally, adding a single ligand to the reaction mixture is not always adequate to yield the desired features. In this review, we discuss in detail the role of the oleic acid/oleylamine ligand pair in the chemical synthesis of nanoparticles. The combined use of these ligands belonging to two different categories of molecules aims to control the size and shape of nanoparticles and prevent their aggregation, not only during their synthesis but also after their dispersion in a carrier solvent. We show how the different binding strengths of these two molecules and their distinct binding modes on specific facets affect the reaction kinetics toward the production of nanostructures with tailored characteristics. Additional functions, such as the reducing function, are also noted, especially for oleylamine. Sometimes, the carboxylic acid will react with the alkylamine to form an acid-base complex, which may serve as a binary capping agent and reductant; however, its reducing capacity may range from lower to much lower than that of oleylamine. The types of nanoparticles synthesized in the simultaneous presence of oleic acid and oleylamine and discussed herein include metal oxides, metal chalcogenides, metals, bimetallic structures, perovskites, upconversion particles and rare earth-based materials. Diverse morphologies, ranging from spherical nanoparticles to anisotropic, core-shell and hetero-structured configurations are presented. Finally, the relation between tuning the resulting surface and volume nanoparticle properties and the relevant applications is highlighted.

The potential of surface nano-engineering in characteristics of cobalt-based nanoparticles and biointerface interaction with prokaryotic and human cells

Cobalt-based nanoparticles (CBNPs) have recently received great attention in biomedical studies; however, the possible biotoxicity of these nanoparticles (NPs) has remained a foremost concern that should be addressed. As surface functionalization is one of the helpful proposed solutions, we aimed to apply Lipoamino acids (LAAs) as a coating agent to improve biocompatibility. To this purpose, cobalt oxide, cobalt ferrite, and iron oxide nanoparticles (IONs) were synthesized with and without 2-amino-hexadecanoic acid coating to assess the impacts of LAA coating on characteristics and biocompatibility of CBNPs in human cells and compare with IONs, a widely used magnetic NPs in biomedicine. Antibacterial activities of NPs were evaluated against four Gram-negative and Gram-positive bacteria species to assess their biointerface interaction with prokaryotic cells. In addition, the antibacterial activities of synthesized NPs were compared to silver NPs, one of the widely used antimicrobial NPs and standard antibiotics (ampicillin). The structural characteristics properties of NPs were analyzed using TEM, FE-SEM, EDS, FTIR, XRD, and VSM. These NPs exhibited sphere-like to polygon-like morphology with desirable mean size. CBNPs displayed dose-dependent cytotoxicity and antimicrobial activities against human cell lines and all tested microbial species, as well as more cytotoxicity and bacterial inhibition compared to IONs. Besides, the results revealed that LAA coating could significantly improve the biocompatibility and antibacterial activity of NPs while impacting magnetic properties. To sum up, it seems that surface functionalization could provide more potent tools for bioapplications with improving biocompatibility and bacterial inhibition of CBNPs, though; further studies are needed in this regard.

Rapid hot-injection as a tool for control of magnetic nanoparticle size and morphology

The rapid hot-injection (HI) technique was employed to synthesize magnetic nanoparticles with well-defined morphology (octahedrons, cubes, and star-like). It was shown that the proposed synthetic approach could be an alternative for the heat-up and flow hot-injection routes. Instant injection of the precursor to the hot reaction mixture (solvent(s) and additives) at high temperatures promotes fast nucleation and particle directional growth towards specific morphologies. We state that the use of saturated hydrocarbon namely hexadecane (sHD) as a new co-solvent affects the activity coefficient of monomers, forces shape-controllable growth, and allows downsizing of particles. We have shown that the rapid hot-injection route can be extended for other ferrites as well (ZnFe₂O₄, CoFe₂O₄, NiFe₂O_4, and MnFe₂O₄) which has not been done previously through the HI process before.

Rapid hot-injection can be used for precise control of magnetic particle shape.

Clearable Nanoparticles for Cancer Photothermal Therapy

Nanoparticles are important mediators for cancer photothermal therapy (PTT) where they can efficiently convert photon energy into heat and ablate the surrounding cancer cells with superior spatial and temporal precision. Recent decades have witnessed a booming development of numerous formulations of PTT nanoparticles that exhibit outstanding anti-tumor efficacy in preclinical studies. However, their clinical translation has been mined by safety concerns, especially their long-term impact on human body. Biodegradable nanoparticles that can be excreted after PTT, therefore, are gaining popularity due to their biocompatibility and improved safety profiles. This chapter provides an update on the progress in clearable PTT nanoparticles for cancer treatment. We discuss their design, synthesis strategy, and physicochemical properties relevant to photothermal performance. We also review their biodistribution patterns and in vivo anti-tumor efficacy, along with their degradation mechanism and clearance kinetics. Lastly, we present a brief overview of the imaging techniques to noninvasively monitor the degradation of PTT nanoparticles.

Magnetic Nanocomposite Hydrogels for Tissue Engineering: Design Concepts and Remote Actuation Strategies to Control Cell Fate

Most tissues of the human body are characterized by highly anisotropic physical properties and biological organization. Hydrogels have been proposed as scaffolding materials to construct artificial tissues due to their water-rich composition, biocompatibility, and tunable properties. However, unmodified hydrogels are typically composed of randomly oriented polymer networks, resulting in homogeneous structures with isotropic properties different from those observed in biological systems. Magnetic materials have been proposed as potential agents to provide hydrogels with the anisotropy required for their use on tissue engineering. Moreover, the intrinsic properties of magnetic nanoparticles enable their use as magnetomechanic remote actuators to control the behavior of the cells encapsulated within the hydrogels under the application of external magnetic fields. In this review, we combine a detailed summary of the main strategies to prepare magnetic nanoparticles showing controlled properties with an analysis of the different approaches available to their incorporation into hydrogels. The application of magnetically responsive nanocomposite hydrogels in the engineering of different tissues is also reviewed.

Coercivity dependence of cation distribution in Co-based spinel: correlating theory and experiments

The inversion degree of a spinel-type nanomaterial is an essential parameter to understand the magnetic and electronic properties of ferrites. By micromagnetic simulations, we were able to connect DFT calculations and experiments for CoFe₂O₄ NPs.

Aminodextran Coated CoFe2O4 Nanoparticles for Combined Magnetic Resonance Imaging and Hyperthermia

Aminodextran (AMD) coated magnetic cobalt ferrite nanoparticles are synthesized via electrostatic adsorption of aminodextran onto magnetic nanoparticles and their potential theranostic application is evaluated. The uncoated and aminodextran-coated nanoparticles are characterized to determine their hydrodynamic size, morphology, chemical composition, zeta potential and magnetization. The aminodextran containing cobalt ferrite nanoparticles of nanometer size are positively charged in the pH range from 3 to 9 and exhibit saturation magnetization of 50 emu/g. The magnetic resonance imaging (MRI) indicates capability for diagnostics and a reduction in intensity with an increase in nanoparticle amount. The hyperthermia capability of the prepared particles shows their potential to generate suitable local heat for therapeutic purposes. There is a rise of 7 °C and 9 °C at 327 kHz and 981 kHz respectively and specific absorption rates (SAR) of aminodextran-coated nanoparticles are calculated to be 259 W/g and 518 W/g at the given frequencies larger than uncoated nanoparticles (0.02 W/g). The development of novel aminodextran coated magnetic cobalt ferrite nanoparticles has significant potential to enable and improve personalized therapy regimens, targeted cancer therapies and ultimately to overcome the prevalence of nonessential and overdosing of healthy tissues and organs.

Fabrication of a multifunctional magnetic-fluorescent material for medical applications

Multifunctional biocompatible materials have evoked considerable interest in the field of medical applications. Here we report the thermal decomposition preparation of homogeneous fluorescent-magnetic particles with a composite structure containing CoFe2O4 nanoparticles as nucleation seeds for fluorescent Gd2-xO3:Eux. The composite exhibited a wide range of fluorescence transitions in the whole visible spectrum, displaying 18 different emission peaks when excited at a 250 nm wavelength. Moreover, at low temperature the peaks of the composite were wider than the peaks of the fluorescent material, which may be attributed to a set of new energy levels due to a combination of Stark splitting with the magnetic field of CoFe2O4. Because this material is intended to be used for biomedical applications, the potential toxicity of the composite was tested using an invertebrate hemocyte cell model. The cells showed slight morphological and biochemical changes upon exposure to the composite; however, there was no increase in cell death at concentrations of up to 40 ppm. In addition, the material could be tracked by its fluorescence inside the cells, when excited at a more bio-friendly and less energetic wavelength of 405 nm. Furthermore, MRI showed T1 and T2 dual contrast with relaxivity values in the range of most reported materials.

Natural arrangement of AgCu bimetallic nanostructures through oleylamine reduction

The use of AgCu bimetallic NPs as a catalyst is highly desired. To accomplish this, the morphology of nanostructures is a key factor.

Recent advancements in manganite perovskites and spinel ferrite-based magnetic nanoparticles for biomedical theranostic applications

Recently, magnetic nanoparticles (MNPs) based on manganite perovskites (La_1-xSr_xMnO₃ or LSMO) and/or spinel ferrites (i.e. SPFs with the formula MFe₂O₄; M=Co, Mg, Mn, Ni and Zn and mixed SPFs (e.g. Co-Zn, Mg-Mn, Mn-Zn and/or Ni-Zn)) have garnered great interest in magnetic hyperthermia therapy (MHT) as heat-inducing agents due to their tuneable magnetic properties including Curie temperature (T _c) to generate controllable therapeutic temperatures (i.e. 42 °C-45 °C)-under the application of an alternating magnetic field (AMF)-for the treatment of cancer. In addition, these nanoparticles are also utilized in magnetic resonance imaging (MRI) as contrast-enhancing agents. However, the employment of the LSMO/SPF-based MNPs in these MHT/MRI applications is majorly influenced by their inherent properties, which are mainly tuned by the synthesis factors. Therefore, in this review article, we have systematically discussed the significant chemical methods used to synthesize the LSMO/SPF-based MNPs and their corresponding intrinsic physicochemical properties (size/shape/crystallinity/dispersibility) and/or magnetic properties (including saturation magnetization (M _s)/T _c). Then, we have analyzed the usage of these MNPs for the effective imaging of cancerous tumors via MRI. Finally, we have reviewed in detail the heating capability (in terms of specific absorption rate) of the LSMO/SPF-based MNPs under calorimetric/biological conditions for efficient cancer treatment via MHT. Herein, we have mainly considered the significant parameters-such as size, surface coating (nature and amount), stoichiometry, concentration and the applied AMFs (including amplitude (H) and frequency (f))-that influence the heat induction ability of these MNPs.

Advances in the Application of Magnetic Nanoparticles for Sensing

Magnetic nanoparticles (MNPs) are of high significance in sensing as they provide viable solutions to the enduring challenges related to lower detection limits and nonspecific effects. The rapid expansion in the applications of MNPs creates a need to overview the current state of the field of MNPs for sensing applications. In this review, the trends and concepts in the literature are critically appraised in terms of the opportunities and limitations of MNPs used for the most advanced sensing applications. The latest progress in MNP sensor technologies is overviewed with a focus on MNP structures and properties, as well as the strategies of incorporating these MNPs into devices. By looking at recent synthetic advancements, and the key challenges that face nanoparticle-based sensors, this review aims to outline how to design, synthesize, and use MNPs to make the most effective and sensitive sensors.

Controlled Overgrowth of Five-Fold Concave Nanoparticles into Plasmonic Nanostars and Their Single-Particle Scattering Properties

Growth of anisotropic nanostructures enables the manipulation of optical properties across the electromagnetic spectrum by fine morphological tuning of the nanoparticles. Among them, stellated metallic nanostructures present enhanced properties owing to their complex shape, and hence, the control over the final morphology becomes of great importance. Herein, a seed-mediated method for the high-yield production of gold_rich-copper concave branched nanostructures and their structural and optical characterization is reported. The synthesis protocol enabled excellent control and tunability of the final morphology, from concave pentagonal nanoparticles to five-fold branched nanoparticles, named "nanostars". The anisotropic shape was achieved via kinetic control over the synthesis conditions by selective passivation of facets using a capping agent and assisted by the presence of copper chloride ions, both having a crucial impact over the final structure. Optical extinction measurements of nanostars in solution indicated a broad spectral response, hiding the properties of the individual nanostars. Hence, single-particle scattering measurements of individual concave pentagonal nanoparticles and concave nanostars were performed to determine the origin of the multiple plasmon bands by correlation with their morphological features, following their growth evolution. Finite-difference time-domain calculations delivered insights into the geometry-dependent plasmonic properties of concave nanostars and their packed aggregates. Our results uncover the intrinsic scattering properties of individual nanostars and the origin of the broad spectral response, which is mostly due to z-direction packed aggregates.

Fluoride ion assisted growth of hierarchical flowerlike nanostructures of Co/Ni ferrites and their magnetoresistive response

One-dimensional nanorod arrays exhibiting hierarchical flowerlike morphologies, of Co and Ni based ferrites were synthesized by hydrothermal treatment and using ammonium fluoride (NH₄F) as a mineralizing agent. The effects of NH₄F concentration and synthesis temperature were probed to control the morphology of these nanorods that were formed as a result of crystal nucleation. It was observed that a higher concentration of NH₄F leads to several other nucleation sites above these nanorods while controlled concentration of precursors and NH₄F results in the synthesis of floral patterns. The specific geometries of these nanorods leads to a shape anisotropy effect resulting in increased magnetic coercive fields. To study the effect of magnetic field on the resistance and current density, impedance spectroscopy and I–V–R characteristics, respectively, were performed. Nanorods show enhanced values for resistance with the increase in magnetic field confirming the effect of magnetoresistive coupling while a decrease in current densities with increasing magnetic field highlights the potential of these structures for magnetoresistive applications.

One-dimensional nanorod arrays of Co/Ni ferrites emerging into hierarchical flowerlike morphologies, prepared by hydrothermal treatment, using ammonium fluoride (NH₄F) as a mineralizing agent.

Targeted T1 Magnetic Resonance Imaging Contrast Enhancement with Extraordinarily Small CoFe2O4 Nanoparticles

Extraordinarily small (2.4 nm) cobalt ferrite nanoparticles (ESCIoNs) were synthesized by a one-pot thermal decomposition approach to study their potential as magnetic resonance imaging (MRI) contrast agents. Fine size control was achieved using oleylamine alone, and annular dark-field scanning transmission electron microscopy revealed highly crystalline cubic spinel particles with atomic resolution. Ligand exchange with dimercaptosuccinic acid rendered the particles stable in physiological conditions with a hydrodynamic diameter of 12 nm. The particles displayed superparamagnetic properties and a low r₂/ r₁ ratio suitable for a T₁ contrast agent. The particles were functionalized with bile acid, which improved biocompatibility by significant reduction of reactive oxygen species generation and is a first step toward liver-targeted T₁ MRI. Our study demonstrates the potential of ESCIoNs as T₁ MRI contrast agents.

Synthesis, structure and magnetic properties of multipod-shaped cobalt ferrite nanocrystals

A non-aqueous sol–gel route followed by oriented attachment to make multi-pod CoFe₂O₄ nanocrystals showing large room temperature saturation magnetization.

Gradient of zinc content in core–shell zinc ferrite nanoparticles – precise study on composition and magnetic properties

Structure, magnetic properties and chemical composition of synthesized zinc ferrite nanoparticles were characterized by a broad spectrum of methods.

Synthesis of size-tuneable β-FeOOH nanoellipsoids and a study of their morphological and compositional changes by reduction

Synthesis of finely size-tuned β-FeOOH nanoellipsoids which could be used as precursors to form anisotropic iron oxide nanoparticles by reduction.

Artificially controlled degradable nanoparticles for contrast switch MRI and programmed cancer therapy

Background

Utilizing the permeability enhancement and irreversible biomolecule denaturation caused by hyperthermia, photothermal-chemo synergistic therapy has shown great potential in clinical cancer treatment.

Purpose

The objective of this study was to provide a novel controlled drug release method to improve the efficiency of photothermal-chemo synergistic therapy.

Patients and methods

HCT116 tumor-bearing mice were selected as modal for the study of cancer theranostics efficiency. The T2 to T1 magnetic resonance imaging contrast switch was studied in vivo. Analyses of the tumor growth of mice were carried out to evaluate the tumor therapy efficiency.

Results

We developed novel artificially controlled degradable Co₃O₄ nanoparticles and explored their potential in drug delivery/release. In the presence of ascorbic acid (AA), the designed nanomaterials can be degraded via a redox process and hence release the loaded drugs. Importantly, the AA, in the lack of l-gulonolactone oxidase, cannot be synthesized in the body of typical mammal including human, which suggested that the degradation process can be controlled artificially. Moreover, the obtained nanoparticles have outstanding photothermal conversion efficiency and their degradation can also result in an magnetic resonance imaging contrast enhancement switch from T₂ to T₁, which benefits the cancer theranostics.

Conclusion

Our results illustrated that the artificially controlled degradable nanoparticles can serve as an alternative candidate for controllable drug release as well as a platform for highly efficient photothermal-chemo synergistic cancer theranostics.

Sandwich-interface inspired strategy for controlled formation of nanoparticles

Nanoparticles are functional materials able to offer improved or new synergetic properties. By manipulating the interfacial properties, we demonstrate an innovative sandwich-interface method capable of forming various monodispersed nanostructures including metals, semiconductors, and inorganic and coordinated nanoparticles. By analysing of the reaction mechanism, we show that reaction time, the height of transition and presence of surfactant have the greatest influence on the formation of the products. These advances in the sandwich-interface synthesis significantly extend the scope of interface synthetic methods, facilitating a new level of structural-architectural control which may lead to future developments in the field of crystallography.

Applications of cobalt ferrite nanoparticles in biomedical nanotechnology

Magnetic nanoparticles (MNPs) are very attractive especially for biomedical applications, among which, iron oxide nanoparticles have received substantial attention in the past decade due to the elemental composition that makes them biocompatible and degradable. However recently, other magnetic nanomaterials such as spinel ferrites that can provide improved magnetic properties such as coercivity and anisotropy without compromising on inherent advantages of iron oxide nanoparticles are being researched for better applicability of MNPs. Among various spinel ferrites, cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) are one of the most explored MNPs. Therefore, the intention of this article is to provide a comprehensive review of CoFe₂O₄ NPs and their inherent properties that make them exceptional candidates, different synthesis methods that influence their properties, and applications of CoFe₂O₄ NPs and their relevant applications that have been considered in biotechnology and bioengineering.

Optimizing the Binding Energy of the Surfactant to Iron Oxide Yields Truly Monodisperse Nanoparticles

Despite the great progress in the synthesis of iron oxide nanoparticles (NPs) using a thermal decomposition method, the production of NPs with low polydispersity index is still challenging. In a thermal decomposition synthesis, oleic acid (OAC) and oleylamine (OAM) are used as surfactants. The surfactants bind to the growth species, thereby controlling the reaction kinetics and hence playing a critical role in the final size and size distribution of the NPs. Finding an optimum molar ratio between the surfactants oleic OAC/OAM is therefore crucial. A systematic experimental and theoretical study, however, on the role of the surfactant ratio is still missing. Here, we present a detailed experimental study on the role of the surfactant ratio in size distribution. We found an optimum OAC/OAM ratio of 3 at which the synthesis yielded truly monodisperse (polydispersity less than 7%) iron oxide NPs without employing any post synthesis size-selective procedures. We performed molecular dynamics simulations and showed that the binding energy of oleate to the NP is maximized at an OAC/OAM ratio of 3. The optimum OAC/OAM ratio of 3 is allowed for the control of the NP size with nanometer precision by simply changing the reaction heating rate. The optimum OAC/OAM ratio has no influence on the crystallinity and the superparamagnetic behavior of the Fe₃O₄ NPs and therefore can be adopted for the scaled-up production of size-controlled monodisperse Fe₃O₄ NPs.

Exploring Reaction Conditions to Improve the Magnetic Response of Cobalt-Doped Ferrite Nanoparticles

With the aim of studying the influence of synthesis parameters in structural and magnetic properties of cobalt-doped magnetite nanoparticles, Fe3-xCoxO₄ (0 < x < 0.15) samples were synthetized by thermal decomposition method at different reaction times (30-120 min). The Co ferrite nanoparticles are monodisperse with diameters between 6 and 11 nm and morphologies depending on reaction times, varying from spheric, cuboctahedral, to cubic. Chemical analysis and X-ray diffraction were used to confirm the composition, high crystallinity, and pure-phase structure. The investigation of the magnetic properties, both magnetization and electronic magnetic resonance, has led the conditions to improve the magnetic response of doped nanoparticles. Magnetization values of 86 emu·g-1 at room temperature (R.T.) have been obtained for the sample with the highest Co content and the highest reflux time. Magnetic characterization also displays a dependence of the magnetic anisotropy constant with the varying cobalt content.

Organozinc Precursor-Derived Crystalline ZnO Nanoparticles: Synthesis, Characterization and Their Spectroscopic Properties

Crystalline ZnO_-ROH and ZnO_-OR (R = Me, Et, iPr, nBu) nanoparticles (NPs) have been successfully synthesized by the thermal decomposition of in-situ-formed organozinc complexes Zn(OR)₂ deriving from the reaction of Zn[N(SiMe₃)₂]₂ with ROH and of the freshly prepared Zn(OR)₂ under an identical condition, respectively. With increasing carbon chain length of alkyl alcohol, the thermal decomposition temperature and dispersibility of in-situ-formed intermediate zinc alkoxides in oleylamine markedly influenced the particle sizes of ZnO_-ROH and its shape (sphere, plate-like aggregations), while a strong diffraction peak-broadening effect is observed with decreasing particle size. For ZnO_-OR NPs, different particle sizes and various morphologies (hollow sphere or cuboid-like rod, solid sphere) are also observed. As a comparison, the calcination of the fresh-prepared Zn(OR)₂ generated ZnO_-R NPs possessing the particle sizes of 5.4~34.1 nm. All crystalline ZnO nanoparticles are characterized using X-ray diffraction analysis, electron microscopy and solid-state ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The size effect caused by confinement of electrons’ movement and the defect centres caused by unpaired electrons on oxygen vacancies or ionized impurity heteroatoms in the crystal lattices are monitored by UV-visible spectroscopy, electron paramagnetic resonance (EPR) and photoluminescent (PL) spectroscopy, respectively. Based on the types of defects determined by EPR signals and correspondingly defect-induced probably appeared PL peak position compared to actual obtained PL spectra, we find that it is difficult to establish a direct relationship between defect types and PL peak position, revealing the complication of the formation of defect types and photoluminescence properties.

Sonochemical synthesis of Gd3+ doped CoFe2O4 spinel ferrite nanoparticles and its physical properties

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe_2-xGd_xO₄; x=0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd³⁺ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe_2-xGd_xO₄ nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd³⁺ substitution in CoFe₂O₄ nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd³⁺ doped cobalt ferrite (CoFe_2-xGd_xO₄; x=0.20) exhibit enhanced dielectric constant (277 at 100Hz) and ac conductivity (20.2×10^-9S/cm at 100Hz). The modulus spectroscopy demonstrated the impact of Gd³⁺ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd³⁺ substitution from 234.32Oe (x=0.00) to 12.60Oe (x=0.05) and further increases from 12.60Oe (x=0.05) to 68.62Oe (x=0.20). Moreover, saturation magnetization decreases with Gd³⁺ substitution from 40.19emu/g (x=0.00) to 21.58emu/g (x=0.20). This work demonstrates that the grain size and cation distribution in Gd³⁺ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications.

Morphology-controlled synthesis and enhanced energy product (BH)max of CoFe2O4 nanoparticles

The (BH)_max value of 2.41 MGOe at room temperature confirmed the capabilities of CoFe₂O₄ NPs in permanent magnets for current technological applications.

High magnetisation, monodisperse and water-dispersible CoFe@Pt core/shell nanoparticles

High magnetisation and monodisperse CoFe alloy nanoparticles are desired for a wide range of biomedical applications. However, these CoFe nanoparticles are prone to oxidation, resulting in the deterioration of their magnetic properties. In the current work, CoFe alloy nanoparticles were prepared by thermal decomposition of cobalt and iron carbonyls in organic solvents at high temperatures. Using a seeded growth method, we successfully synthesised chemically stable CoFe@Pt core/shell nanostructures. The obtained core/shell nanoparticles have high saturation magnetisation up to 135 emu g^-1. The magnetisation value of the core/shell nanoparticles remains 93 emu g^-1 after being exposed to air for 12 weeks. Hydrophobic CoFe@Pt nanoparticles were rendered water-dispersible by encapsulating with poly(maleic anhydride-alt-1-octadecene) (PMAO). These nanoparticles were stable in water for at least 3 months and in a wide range of pH from 2 to 11.

Surfactant-Mediated Resistance to Surface Oxidation in MnO Nanostructures

The intrinsic physical properties of nanostructures of metals and their oxides are altered when they are prone to surface oxidation in ambient atmosphere. To overcome this limitation, novel synthesis methodologies are required. In this study, solid octahedral shapes of MnO limit the inward oxygen diffusion compared to that of the MnO-nanoparticle-assembled octahedra. In addition to morphology control, which restricts the thickness of the Mn₃O₄ surface layer, the binding chemistry of the surfactants plays an essential role. For example, the Mn₃O₄ surface layer is 0.4 nm thinner with trioctylphosphine oxide than with trioctylamine as the surfactant. The nanostructures were prepared by varying the surfactants, surfactant-to-precursor molar ratio, accelerating agent, and reaction heating rate. The surface oxidation of MnO nano-octahedra was probed by Rietveld analysis of X-ray diffraction patterns and X-ray photoelectron spectroscopy and characterized by magnetic measurements, as the presence of ferrimagnetic Mn₃O₄ shell on the antiferromagnetic MnO core provides an exchange coupling at the core-shell interface. Thicker the Mn₃O₄ shell, higher is the exchange-biased hysteresis loop shift.

Economically attractive route for the preparation of high quality magnetic nanoparticles by the thermal decomposition of iron(III) acetylacetonate

The thermal decomposition (TD) methods are among the most successful in obtaining magnetic nanoparticles with a high degree of control of size and narrow particle size distribution. Here we investigated the TD of iron(III) acetylacetonate in the presence of oleic acid, oleylamine, and a series of alcohols in order to disclose their role and also investigate economically attractive alternatives for the synthesis of iron oxide nanoparticles without compromising their size and shape control. We have found that some affordable and reasonably less priced alcohols, such as 1,2-octanediol and cyclohexanol, may replace the commonly used and expensive 1,2-hexadecanediol, providing an economically attractive route for the synthesis of high quality magnetic nanoparticles. The relative cost for the preparation of Fe₃O₄ NPs is reduced to only 21% and 9% of the original cost when using 1,2-octanediol and cyclohexanol, respectively.

Development of europium doped core-shell silica cobalt ferrite functionalized nanoparticles for magnetic resonance imaging

The size, shape and chemical composition of europium (Eu3+) cobalt ferrite (CFEu) nanoparticles were optimized for use as a "multimodal imaging nanoprobe" for combined fluorescence and magnetic resonance bioimaging. Doping Eu3+ ions into a CF structure imparts unique bioimaging and magnetic properties to the nanostructure that can be used for real-time screening of targeted nanoformulations for tissue biodistribution assessment. The CFEu nanoparticles (size ∼7.2nm) were prepared by solvothermal techniques and encapsulated into poloxamer 407-coated mesoporous silica (Si-P407) to form superparamagnetic monodisperse Si-CFEu nanoparticles with a size of ∼140nm. Folic acid (FA) nanoparticle decoration (FA-Si-CFEu, size ∼140nm) facilitated monocyte-derived macrophage (MDM) targeting. FA-Si-CFEu MDM uptake and retention was higher than seen with Si-CFEu nanoparticles. The transverse relaxivity of both Si-CFEu and FA-Si-CFEu particles were r2=433.42mM-1s-1 and r2=419.52mM-1s-1 (in saline) and r2=736.57mM-1s-1 and r2=814.41mM-1s-1 (in MDM), respectively. The results were greater than a log order-of-magnitude than what was observed at replicate iron concentrations for ultrasmall superparamagnetic iron oxide (USPIO) particles (r2=31.15mM-1s-1 in saline) and paralleled data sets obtained for T2 magnetic resonance imaging. We now provide a developmental opportunity to employ these novel particles for theranostic drug distribution and efficacy evaluations.

STATEMENT OF SIGNIFICANCE

A novel europium (Eu3+) doped cobalt ferrite (Si-CFEu) nanoparticle was produced for use as a bioimaging probe. Its notable multifunctional, fluorescence and imaging properties, allows rapid screening of future drug biodistribution. Decoration of the Si-CFEu particles with folic acid increased its sensitivity and specificity for magnetic resonance imaging over a more conventional ultrasmall superparamagnetic iron oxide particles. The future use of these particles in theranostic tests will serve as a platform for designing improved drug delivery strategies to combat inflammatory and infectious diseases.