Synthesis of magnetite/amphiphilic polymer composite nanoparticles as potential theragnostic agents

This study describes the synthesis of magnetite/amphiphilic polymer composite nanoparticles that can be potentially used simultaneously for cancer diagnosis and therapy. The synthesis method was a one-shot process wherein magnetite nanoparticles were mixed with core-crosslinked amphiphilic polymer (CCAP) nanoparticles, prepared using a copolymer of a urethane acrylate nonionomer (UAN) and a urethane acrylate anionomer (UAA). The CCAP nanoparticles had a hydrophobic core and a hydrophilic exterior with both PEG segments and carboxylic acid groups, wherein the magnetite nanoparticles were coordinated and stabilized. According to DLS data, the ratio of UAN to UAA and the ratio of magnetite to polymer are keys to controlling the size and thus, the stability of the composite nanoparticles. The magnetic measurement indicated that the composite nanoparticles had superparamagnetic properties and high saturation magnetization. The preliminary magnetic resonance imaging showed that the particles produced an enhanced image even when their concentration was as low as 80 microg/ml.     

Preparation of hollow spherical magnetite nanoparticles

We have developed and tested procedures for the synthesis of hollow spherical magnetite nanoparticles and analyzed the general mechanisms of their formation in relation to their structure and morphology. The phase composition, elemental composition, and morphology of the synthesized particles have been examined by X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy, and their magnetic properties have been studied by an induction method using a vibrating sample magnetometer. The results demonstrate that the proposed procedures enable the preparation of hollow porous spherical magnetite particles 40 nm to 100 μm in diameter, with a wall thickness ≃d/10 and a narrow size distribution.     

Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.     

Thermal stability of silica-coated magnetite nanoparticles prepared by an electrochemical method

Magnetite nanoparticles have been prepared by electrooxidation of iron in water. Surface modifications have been conducted by coating the nanoparticles with silica by a one-step synthesis in dilute sodium silicate solution. The mean size of particles was approximately 10–30 nm for the uncoated particles and 9–12 nm for the coated particles. The results obtained from thermal gravimetric/differential thermal analysis (TG/DTA) revealed that the silica layer formed by the electrochemical method was stable and could serve as a protective layer. Annealing the nanoparticles at 550 °C for 30 min converts magnetite into maghemite for the silica-coated particles, and it further converts the uncoated particles into hematite. The conversions cause the saturation magnetization to decrease for all samples.     

Role of proteins in controlling selenium nanoparticle size

This work investigates the potential for harnessing the association of bacterial proteins to biogenic selenium nanoparticles (SeNPs) to control the size distribution and the morphology of the resultant SeNPs. We conducted a proteomic study and compared proteins associated with biogenic SeNPs produced by E.?coli to chemically synthesized SeNPs as well as magnetite nanoparticles. We identified four proteins (AdhP, Idh, OmpC, AceA) that bound specifically to SeNPs and observed a narrower size distribution as well as more spherical morphology when the particles were synthesized chemically in the presence of proteins. A more detailed study of AdhP (alcohol dehydrogenase propanol-preferring) confirmed the strong affinity of this protein for the SeNP surface and revealed that this protein controlled the size distribution of the SeNPs and yielded a narrow size distribution with a three-fold decrease in the median size. These results support the assertion that protein may become an important tool in the industrial-scale synthesis of SeNPs of uniform size and properties.     

Synthesis and kinetic shape and size evolution of magnetite nanoparticles

Eleven nanometers of magnetite nanoparticles were synthesized by using 6 nm magnetite nanoparticles as seeds and Fe(acac)₃ as precursor at high temperature. Growth kinetics of magnetite nanoparticles was studied during the progress of reaction. Magnetite nanoparticles with different shapes including near-sphere, tetrahedral, truncated tetrahedral and cubic were observed at different reaction time. Transmission electron microscopic results show that the shape and size distributions are time- and temperature-dependent. Hydrodynamic diameter results give the kinetic size distribution changes of magnetite nanoparticles during the reaction, which suggest that this synthesis underwent a “growth-controlled nucleation”.     

Tuning of magnetite nanoparticles to hyperthermic thermoseed by controlled spray method

Magnetite nanoparticles with super-paramagnetic properties have great potential to achieve advances in fields such as hyperthermia, magnetic resonance imaging and magnetic drug targeting. In particular, magnetic particles less than 50 nm are easily incorporated into cells and generate heat under an alternating magnetic field by hysteresis loss. Various methods of preparing magnetic particles have attracted attention, such as spray pyrolysis, microwave irradiation of ferrous hydroxide, microemulsion technique and hydrothermial preparation technique. In this study, magnetite nanoparticles were synthesized with various molar ratio of Fe²⁺ and Fe³⁺ by coprecipitation using spray-guns and dropping syringe. Experiments at different molar concentrations of Fe ions were conducted, which shows the ideal molar concentration of Fe²⁺ to be 0.5 M for pure magnetite. Both in the spray and drop method, pure magnetite nanoparticles could be synthesized when the molar concentration of Fe²⁺ was 0.5 M. With increasing the molar ratio of Fe²⁺, the particle size of the magnetite nanoparticles was increased. The smallest size could be reduced to approximately 7 nm by the spray method. The shape of the synthesized nanoparticles was nearly spherical. The calculated highest loss power by hysteresis losses was 597 W/g, generated with a molar concentration ratio of 0.5:1 (Fe²⁺:Fe³⁺).     

Size control of magnetite nanoparticles by organic solvent-free chemical coprecipitation at room temperature

This study provides a facile single-step coprecipitation method for preparing size-controlled high crystalline magnetite nanoparticles in water system without using any organic solvents. In this method, an iron ions solution and an alkaline solution are simply mixed at room temperature without using any additional heating treatment. The size of obtained magnetite nanoparticles greatly depended on the coexisting anionic species in the starting solution because the coexisting anions greatly influenced both the formation of crystal nuclei and the dispersion stabilisation of formed precipitates. The size control of magnetite nanoparticles having high crystallinity and ferromagnetic property could be successfully achieved by using the effects of coexisting anions. For synthesising finer magnetite nanoparticles, the presence of lactate ion in the starting solution was effective, and coarser ones could be synthesised under higher ferrous/ferric ions molar ratios.     

Synthesis of monodisperse iron oxide and iron/iron oxide core/shell nanoparticles via iron-oleylamine complex

Monodisperse magnetic nanoparticles are of great scientific and technical interests. This paper reports a single-step synthesis of monodisperse magnetite nanoparticles with particle size of 8 nm. Iron/maghaemite core/shell nanoparticles with particle size of 11 nm were obtained by reducing the concentration of oleylamine. TEM and in-situ FTIR results suggested that iron-oleylamine intermediate was generated in-situ and decomposed at higher temperature. Oleylamine was also found on the surface of nanoparticles, indicating its role as capping agent which provided steric protection of as-synthesized nanoparticles from agglomeration. Both magnetite and iron/maghaemite core/shell nanoparticles were superparamagnetic at room temperature with a blocking temperature at 80 K and 67 K, respectively.     

Synthesis and characterization of magnetite nanoparticles via the chemical co-precipitation method

Magnetite nanoparticles were synthesized via the chemical co-precipitation method using ammonium hydroxide as the precipitating agent. The size of the magnetite nanoparticles was carefully controlled by varying the reaction temperature and through the surface modification. Herein, the hexanoic acid and oleic acid were introduced as the coating agents during the initial crystallization phase of the magnetite. Their structure and morphology were characterized by the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and the field-emission scanning electron microscopy (FE-SEM). Moreover, the electrical and magnetic properties were studied by using a conductivity meter and a vibrating sample magnetometer (VSM), respectively. Both of the bare magnetite and the coated magnetite were of the cubic spinel structure and the spherical-shaped morphology. The reaction temperature and the surface modification critically affected the particle size, the electrical conductivity, and the magnetic properties of these particles. The particle size of the magnetite was increased through the surface modification and reaction temperature. In this study, the particle size of the magnetite nanoparticles was successfully controlled to be in the range of 10–40 nm, suitable for various biomedical applications. The electrical conductivity of the smallest particle size was 1.3 × 10^?3 S/cm, within the semi-conductive materials range, which was higher than that of the largest particle by about 5 times. All of the magnetite nanoparticles showed the superparamagnetic behavior with high saturation magnetization. Furthermore, the highest magnetization was 58.72 emu/g obtained from the hexanoic acid coated magnetite nanoparticles.     

Synthesis and physical characterization of magnetite nanoparticles for biomedical applications

Iron oxide nanoparticles for biomedical applications in the size range of 15–130 nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous/ferric chloride solutions. The magnetite particle size is controlled by variation of pH and temperature. The synthesized magnetite nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24 wt% Fe²⁺ and lattice parameters of a₀ ≤ 8.39 Å which are smaller compared to 8.39 Å for stoichiometric magnetite. The extend of oxidation increases with decreasing particle size. Heating at 150–350 °C topotactically transforms the magnetite nanoparticles into stoichiometric tetragonal maghemite (ferrous ion concentration c_Fe²⁺=0 and a₀ = 8.34 Å) without significant particle growth. The magnetite–maghemite transformation is studied with thermal analysis, XRD and IR spectroscopy. The saturation magnetizations of the magnetite and maghemite particles decrease with decreasing particle size. The variation of M_s with particle size is interpreted using a magnetic core–shell particle model. Magnetite particles with d ≤ 16 nm show superparamagnetic behavior at room temperature whereas particles with diameter >16 nm display hysteresis behavior. These particles are candidates for biomedical applications, e.g. controlled drug release or hyperthermia.     

Structure and Magnetic Properties of Polymer Microspheres Filled with Magnetite Nanoparticles

The structure and magnetic properties of collagen microspheres filled with magnetite nanoparticles are studied. The average interparticle separation in the polymer matrix and the size of magnetite nanoparticles before and after the introduction of the nanoparticles into the matrix are determined using electron microscopy. The magnetization curve of the microspheres has a superparamagnetic character. The magnetite nanoparticles undergo no aggregation during the synthesis of microspheres and are evenly distributed over the matrix. The magnetic susceptibility data for magnetic polymer microspheres of different diameters suggest that, at small diameters (<300 m), all of the nanoparticles, aligned in chains, contribute to magnetization; at large diameters, some of the chains give way to clusters, the chains are shorter, and, accordingly, the susceptibility is lower.     

Novel drug delivery system by surface modified magnetic nanoparticles

In the recent progress of gene and cell therapy, novel drug delivery system (DDS) has been required for efficient delivery of small molecules/drugs and also the safety for clinical usage. We have already developed the unique transfection technique by preparing magnetic vector and using permanent magnet. This technique can improve the transfection efficiency. In this study, we directly associated plasmid DNA with magnetic nanoparticles, which can potentially enhance their transfection efficiency by magnetic force. Magnetic nanoparticle, such as magnetite, its average size of 18.7 nm, can be navigated by magnetic force and is basically consisted with oxidized Fe that is commonly used as the supplement drug for anemia. The magnetite particles coated with protamine sulfate, which gives a cationic surface charge onto the magnetite particle, significantly enhanced the transfection efficiency in vitro cell culture system. The magnetite particles coated with protamine sulfate also easily associated with cell surface, leading to high magnetic seeding percentage. From these results, it was found that the size and surface chemistry of magnetic particles would be tailored to meet specific demands on physical and biological characteristics accordingly. Overall, magnetic nanoparticles with different surface modification enhance the association with plasmid DNA and cell surface as well as HVJ-E, which potentially help to improve the drug delivery system.     

Bi-layered polymer–magnetite core/shell particles: synthesis and characterization

Polymer magnetic core particles receive growing attention due to these materials owing magnetic properties which are widely used in different applications. The prepared composite particles are characterized with different properties namely: a magnetic core, a hydrophobic first shell, and finally an external second hydrophilic shell. The present study describes a method for the preparation of bi-layered polymer magnetic core particles (diameter range is 50–150 nm). This method comprises several steps including the precipitation of the magnetic iron oxide, coating the magnetite with oleic acid, attaching the first polymer shell by miniemulsion polymerization and finally introducing hydrophilic surface properties by condensation polymerization. The first step is the formation of magnetite nanoparticles within a co-precipitation process using oleic acid as the stabilizing agent for magnetite. The second step is the encapsulation of magnetite into polyvinylbenzyl chloride particles by miniemulsion polymerization to form a magnetic core with a hydrophobic polymer shell. The hydrophobic shell is desired to protect magnetite nanoparticles against chemical attack. The third step is the coating of magnetic core hydrophobic polymer shell composites with a hydrophilic layer of polyethylene glycol by condensation polymerization. Regarding the miniemulsion polymerization the influence of the amount of water, the mixing intensity and the surfactant concentration were studied with respect to the formation of particles which can be further used in chemical engineering applications. The resulting magnetic polymer nanoparticles were characterized by particle size measurement, chemical stability, iron content, TEM, SEM, and IR.     

Magnetic properties of magnetite nanoparticles coated with mesoporous silica by sonochemical method

In this paper we present the magnetic properties of mesoporous silica-coated Fe₃O₄ nanoparticles. The coating of magnetite nanoparticles with mesoporous silica shell was performed under ultrasonic irradiation. The obtained mesoporous silica-coated magnetite nanoparticles were characterized by powder X-ray diffraction, focused ion beam-scanning electron microscopy, nitrogen adsorption-desorption isotherms and vibrating sample magnetometer. The hysteretic behavior was studied using first-order reversal curves diagrams. The X-ray diffraction result indicates that the extreme chemical and physical conditions created by acoustic cavitations have an insignificant effect on crystallographic structural characteristic of magnetite nanoparticles. Changes in the coercivity distributions of the magnetite nanoparticles were observed on the first-order reversal curves diagrams for the samples with coated particles compared with the samples containing uncoated particles of magnetite. The coated particles show an increased most probable coercivity of about 20% compared with the uncoated particles which can be associated with an increased anisotropy due to coating even if the interaction field distribution measured on the diagrams are virtually identical for coated/uncoated samples.     

Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens

The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50?nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form.     

A novel method to prepare magnetic nanoparticles: precipitation in bicontinuous microemulsions

A novel method to prepare iron oxide nanoparticles by precipitation in bicontinuous microemulsions is reported. Precipitation reactions were carried out in microemulsions stabilized with a mixture of dodecyltrimethylammonium bromide/didodecyldimethylammonium bromide (3/2, w/w). Nanoparticles were characterized by X-ray diffraction, transmission electronic microscopy (TEM) and vibrating sample magnetometry (VSM), and consisted of magnetite or a mixture of magnetite and maghemite. The particles have an average diameter of 8 nm with a relatively narrow particle size distribution and show possible superparamagnetic behavior. Noticeably higher yields of precipitate are observed for this new approach in comparison with those typicall obtained using reverse microemulsions.     

Solvothermal‐assisted green synthesis of hybrid Chi‐Fe3 O4 nanocomposites: a potential antibacterial and antibiofilm material

In this present study, a hybrid Chi‐Fe₃ O₄ was prepared, characterised and evaluated for its antibacterial and antibiofilm potential against Staphylococcus aureus and Staphylococcus marcescens bacterial pathogens. Intense peak around 260 nm in the ultraviolet–visible spectrum specify the formation of magnetite nanoparticles. Spherical‐shaped particles with less agglomeration and particle size distribution of 3.78–46.40 nm were observed using transmission electron microscopy analysis and strong interaction of chitosan with the surface of magnetite nanoparticles was studied using field emission scanning microscopy (FESEM). X‐ray diffraction analysis exhibited the polycrystalline and spinel structure configuration of the nanocomposite. Presence of Fe and O, C and Cl elements were confirmed using energy dispersive X‐ray microanalysis. Fourier transform infrared spectroscopic analysis showed the reduction and formation of Chi‐Fe₃ O₄ nanocomposite. The antibacterial activity by deformation of the bacterial cell walls on treatment with Chi‐Fe₃ O₄ nanocomposite and its interaction was visualised using FESEM and the antibiofilm activity was determined using antibiofilm assay. In conclusion, this present study shows the green synthesis of Chi‐Fe₃ O₄ nanocomposite and evaluation of its antibacterial and antibiofilm potential, proving its significance in medical and biological applicationsInspec keywords: visible spectra, particle size, magnetic particles, nanocomposites, nanoparticles, X‐ray diffraction, nanofabrication, transmission electron microscopy, X‐ray chemical analysis, nanomagnetics, microorganisms, antibacterial activity, iron compounds, ultraviolet spectra, biomedical materials, field emission scanning electron microscopy, Fourier transform infrared spectra, filled polymers, crystal growth from solution, polymer structureOther keywords: potential antibacterial material, antibiofilm potential, magnetite nanoparticles, solvothermal‐assisted green synthesis, hybrid Chi‐Fe₃ O₄ nanocomposites, staphylococcus aureus, staphylococcus marcescens, bacterial pathogens, ultraviolet–visible spectrum, spherical‐shaped particles, particle size, transmission electron microscopy, FESEM, field emission scanning electron microscopy, X‐ray diffraction, spinel structure, polycrystalline structure, energy dispersive X‐ray microanalysis, Fourier transform infrared spectroscopic analysis, deformation, bacterial cell walls, Fe₃ O₄      

Size distribution function of magnetite nanoparticles in disperse systems

A size distribution function of magnetite nanoparticles has been selected among known distribution functions that well represent the frequency polygon of the nanoparticles. Normal and lognormal distribution functions are shown to provide more accurate representations for the initial and final portions of the size distribution of magnetite nanoparticles. We have determined the transition diameter of magnetite nanoparticles which corresponds to a transition from a normal to a lognormal distribution function and have constructed a composite distribution function consisting of normal and lognormal distribution functions, which accurately represents the size distribution of the magnetite nanoparticles. The distribution moments and magnetization curve calculated using this distribution function agree well with the moments calculated using the frequency polygon of the magnetite nanoparticles and with the experimentally determined magnetization curve.