Particle size dependence of relaxivity for silica-coated iron oxide nanoparticles

We investigate the particle size dependence of the relaxivity of hydrogen protons in an aqueous solution of iron oxide (Fe₃O₄) nanoparticles coated in silica for biocompatibility. The T₁ and T₂ relaxation times for various concentrations of silica-coated nanoparticles were determined by a magnetic resonance scanner. We find that the relaxivity increased linearly with increasing particle size. The T₂ relaxivity (R₂) is more than 50 times larger than the T₁ relaxivity (R₁) for the nanoparticle contrast agent, which reflects the fact that the T₂ relaxation is mainly influenced by outer sphere processes. The high R₂/R₁ ratio demonstrates that silica-coated iron oxide nanoparticles may serve as a T₂ contrast agents in magnetic resonance imaging with high efficacy.     

One-pot synthesis of amphiphilic superparamagnetic FePt nanoparticles and magnetic resonance imaging in vitro

Monodispersed amphiphilic FePt nanoparticles with the diameter of about 4 nm were synthesized by high temperature pyrolysis of iron(III) acetylacetonate and platinum(II) acetylacetonate. Their amphiphilicity is contributed to the tetraethylene glycol (TEG) and oleic acid (OA) on the surface, which is confirmed by FTIR and XPS spectra. They provide a superparamagnetic property with the saturation magnetization (Ms) of about 25 emu/g and the transverse relaxivity (r₂) of about 122.6 mM⁻¹ s⁻¹ in aqueous solutions. Furthermore, FePt nanoparticles show low cytotoxicity in living cells. They can be uptaken by HeLa cells effectively and result in the obvious decrease of T₂ relaxation time after internalization.     

Dextran‐Coated Antiferromagnetic MnO Nanoparticles for a T1‐MRI Contrast Agent with High Colloidal Stability

A simple approach to synthesize carboxymethyl dextran‐coated MnO nanoparticles (CMDex‐MnONPs) with high colloidal stability in physiological saline solutions is described here for potential applications as a magnetic resonance imaging (MRI) T₁ contrast agent. The thermal decomposition methodology is used to produce uniform MnONPs with an average size of around 20 nm, and its hydrophobic surface is modified with CMDex molecules, conferring hydrophilic properties. After CMDex coating, the nanoparticle presents high colloidal stability in concentrations ranging from 10 to 50 μg mL^?1, average hydrodynamic size (Z‐average) of 130 nm, polydispersity degree of ≈12%, and negative surface charge in both simulated body fluid solutions and pure water with zeta‐potential of –20 and –40 mV, respectively. The CMDex‐MnONPs with 20 nm show antiferromagnetic behavior at room temperature, and the magnetic properties are found to be strongly dependent of the nanoparticle size, increasing the contribution of the ferromagnetic Mn₃O₄ phase with decreasing size for nanoparticles about 3 nm. Cytotoxicity evaluation in cancerous and noncancerous cells in the range of 5.0–50.0 μg mL^?1 shows low toxicity for cancerous cells and lack of the same for healthy cells lines. Related to the magnetic properties, CMDex‐MnONP presents significant r₁ relaxivity and low r₂/r₁ relaxivity ratio. The results suggest that these nanoparticles display characteristics for potential applications as an MRI T₁ contrast agent.     

Synthesis of N-deficient GaN nanoparticles and its enhanced dielectric response

In this paper, GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent cyanamide (CN₂H₂) and Ga₂O₃ as precursors. The structural properties were investigated in detail. It is found that these nanoparticles having average size of 40 nm were N-deficient with the N vacancies reaching as high as 12%. The Raman scattering spectrum of these nanoparticles presented some interesting features. The room-temperature frequency spectrum of the relative dielectric constant ?_r was measured and indicated that these nanoparticles exhibited sharp enhancement at low frequency range comparing with GaN nanomaterials and N-deficient microparticles. It is thought both the rotation direction polarization (RDP) and the space charge polarization (SCP) process should be responsible for the enhancement of ?_r in these N-deficient GaN nanoparticles.     

T1 and T2 relaxivities of succimer-coated MFe2O4 (M=Mn, Fe and Co) inverse spinel ferrites for potential use as phase-contrast agents in medical MRI

Superparamagnetic MFe₂³⁺O₄ (M=Mn²⁺, Fe²⁺ and Co²⁺) inverse spinel ferrite (ISF) nanoparticles with narrow size distribution having average diameters of 6-8 nm were synthesized by a diol reduction of organic metals and the surface was modified to be hydrophilic by coating with succimer. Magnetic resonance imaging (MRI) contrast enhancement by dipolar coupling defined interactions between the synthesized ISFs and protons in the bulk water was investigated with initial susceptibility, magnetization and anisotropy of the succimer-coated ISFs. The relaxivity ratios, r₂/r₁, for MnFe₂O₄, Fe₃O₄ and CoFe₂O₄ were measured to be 12.2, 23.1 and 62.3, respectively, which demonstrate the potential usefulness of these magnetic nanoparticles as T₂ contrast agents for MRI.     

Nanoscale assembly of amine-functionalized colloidal iron oxide

We demonstrate a single-step facile approach for highly water-stable assembly of amine-functionalized Fe₃O₄ nanoparticles using thermal decomposition of Fe-chloride precursors in ethylene glycol medium in the presence of ethylenediamine. The average size of nanoassemblies is 40±1 nm, wherein the individual nanoparticles are about 6 nm. Amine-functionalized properties are evident from Fourier transform infrared spectrometer (FTIR), thermal and elemental analyses. The saturation magnetization and spin-echo r₂ of the nanoassemblies were measured to be 64.3 emu/g and 314.6 mM⁻¹ s⁻¹, respectively. The higher value of relaxivity ratio (r₂/r₁=143) indicates that nanoassemblies are a promising high-efficiency T2 contrast agent platform.     

Trinuclear Gd(III) Metal Complex with Amide Core Display Remarkable Enhancement in Relaxivity

New trinuclear gadolinium(III) complex having 2-bromoisovaleric acid pendant arm is reported. The longitudinal relaxivity (r _1p) of the complex is 23.17 mM^?1 s^?1 which correspond to a “per Gd” relaxivity of 7.72 mM^?1 s^?1. The transverse relaxivity (r _2p) of the complex is 24.79 mM^?1 s^?1 which correspond to a “per Gd” value of 8.26. The complex exhibit r _1p and r _2p values of 29.19 and 35.20, respectively, in the presence of HSA. The complex also shows pH dependant relaxivity which is an added advantage of the complex for utilization in cancer cell magnetic resonance imaging. The higher relaxivity values in water and HSA indicates a compact solution structure for the complexes and a restricted internal motion about the amide spacer.     

Facile Synthesis of Manganese Tellurite Nanoparticles for Magnetic Resonance Imaging-Guided Photothermal Therapy

In this study, manganese tellurite (MnTeO₃) nanoparticles are developed as theranostic agents for magnetic resonance imaging (MRI)-guided photothermal therapy of tumor. MnTeO₃ nanoparticles are synthesized via a simple one-step method. The as-synthesized MnTeO₃ nanoparticles with uniform size show good biocompatibility. In particular, MnTeO₃ nanoparticles exhibit a high photothermal conversion efficiency (η = 26.3%), which is higher than that of gold nanorods. Moreover, MnTeO₃ nanoparticles also have high MRI performance. The longitudinal relaxivity (r₁) value of MnTeO₃ nanoparticles is determined to be 8.08 ± 0.2 mm ⁻¹ s⁻¹, which is higher than that of clinically approved T₁-contrast agents Gd-DTPA (4.49 ± 0.1 mm ⁻¹ s⁻¹). The subsequent MnTeO₃ nanoparticles-mediated photothermal therapy displays a highly efficient ablation of tumor cells both in vitro and in vivo with negligible toxicity. It is demonstrated that MnTeO₃ nanoparticles can serve as promising theranostic agents with great potentials for MRI-guided photothermal therapy.     

Paramagnetic liposomes as MRI contrast agents: influence of liposomal physicochemical properties on the in vitro relaxivity

The in vitro contrast efficacy of liposome encapsulated gadolinium-[10-(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] (GdHPDO3A) has been assessed by relaxometry. The internal concentrations were 150 and 250 mM Gd. Two types of liposome compositions were investigated: a phospholipid blend consisting of both hydrogenated phosphatidylcholine (HPC) and phosphatidylserine (HPS) with a gel-to-liquid crystalline phase transition temperature (T_m) of 50°C, and a mixture of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) with a T_m of 41°C. The investigated liposome size range was 70–400 nm. The T₁ and T₂ relaxivities (r₁ and r₂) of liposome encapsulated GdHPDO3A were significantly reduced at 37°C and 0.47 T, compared to those of non-liposomal metal chelate, due to an exchange limitation of the dipolar relaxation process. The highest relaxivity values were obtained for the DPPC/DPPG liposomes, and were attributed to a higher liposome water permeability and to a more efficient water exchange across the membrane. A reduction in liposome size increased the r₁, confirming the exchange limited dipolar relaxation. The increased r₁ with increasing temperature demonstrated the prerequisite of rapid water exchange between the interior and exterior of the liposome for efficient dipolar relaxation enhancement. Susceptibility effects were present in the liposome systems as the r₂/r₁ ratio increased with increasing liposome size and internal Gd concentration. In summary, the current work has shown the influence of key physicochemical properties, such as liposome size, membrane composition and permeability, on the in vitro relaxivity of liposome encapsulated GdHPDO3A.     

Responsible nanotechnology development

Chelated gadolinium ions, e.g., Gd-DTPA, are today used clinically as contrast agents for magnetic resonance imaging (MRI). An attractive alternative contrast agent is composed of gadolinium oxide nanoparticles as they have shown to provide enhanced contrast and, in principle, more straightforward molecular capping possibilities. In this study, we report a new, simple, and polyol-free way of synthesizing 4?C5-nm-sized Gd₂O₃ nanoparticles at room temperature, with high stability and water solubility. The nanoparticles induce high-proton relaxivity compared to Gd-DTPA showing r ₁ and r ₂ values almost as high as those for free Gd³⁺ ions in water. The Gd₂O₃ nanoparticles are capped with acetate and carbonate groups, as shown with infrared spectroscopy, near-edge X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and combined thermogravimetric and mass spectroscopy analysis. Interpretation of infrared spectroscopy data is corroborated by extensive quantum chemical calculations. This nanomaterial is easily prepared and has promising properties to function as a core in a future contrast agent for MRI.     

分子动力学模拟尺寸对纳米Cu颗粒等温晶化过程的影响

采用分子动力学方法和镶嵌原子势, 模拟了4000个Cu原子和13500个Cu原子(简称Cu₄₀₀₀和Cu₁₃₅₀₀)组成的纳米颗粒以及块体Cu的等温晶化过程. 通过对这些颗粒在晶化过程中结构和动力学行为的分析研究, 发现低温时, 不同尺寸的纳米Cu颗粒均出现多步晶化, 且晶化时间的分布曲线远比高温时范围大; 除了温度, 颗粒尺寸对晶化行为也有重要的影响, 尺寸越大, 晶化时间越长, 最终的晶化程度越高; 但是晶化时间随尺寸增大而增加的趋势不会一直持续, 发现存在一个临界尺寸r_c, 小于r_c时, 晶化时间随颗粒尺寸增大而增加, 大于r_c时,晶化时间随尺寸增大而减小.     

Superparamagnetic silica nanoparticles with immobilized metal affinity ligands for protein adsorption

Superparamagnetic silica-coated magnetite (Fe₃O₄) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution. Then silica was coated on the Fe₃O₄ nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu²⁺, the magnetic silica nanoparticles with immobilized Cu²⁺ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.     

Size-dependent spin-reorientation transition in Nd2Fe14B nanoparticles

It is well known that some ferromagnetic properties like Curie temperature are size dependent. In this Letter we will report that the spin-reorientation temperature of Nd₂Fe₁₄B material is also size dependent. By using a surfactant-assisted ball milling technique, Nd₂Fe₁₄B nanoparticles with different size about 6, 20 and 300 nm were successfully obtained. Spin-reorientation transition temperature of the NdFeB nanoparticles was then determined by measuring the temperature dependence of DC and AC magnetic susceptibility. It was revealed that the spin-reorientation transition temperature (Tsr) of the nanoparticles is strongly size dependent. Tsr of the 300 nm particles is lower than that of the bulk raw material while the Tsr of the 20 nm particles is significantly lower than that for the 300 nm particles. The physics behind this size dependence is discussed.     

Synthesis of aqueous ferrofluids of ZnxFe3−xO4 nanoparticles by citric acid assisted hydrothermal-reduction route for magnetic hyperthermia applications

Superparamagnetic and monodispersed aqueous ferrofluids of Zn substituted magnetite nanoparticles (Zn_xFe_3−xO₄, x=0, 0.25, 0.3, 0.37 and 0.4) were synthesized via hydrothermal-reduction route in the presence of citric acid, which is a facile, low energy and environmental friendly method. The synthesized nanoparticles were characterized by X ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and the dynamic light scattering (DLS) method. The results showed that a certain amount of citric acid was required to obtain single phase Zn substituted magnetite nanoparticles. Citric acid acted as a modulator and reducing agent in the formation of spinel structure and controlled nanoparticle size and crystallinity. Mean particle sizes of the prepared nanoparticles were around 10 nm. The results that are obtained from XRD, magnetic and power loss measurements showed that the crystallinity, saturation magnetization (M_S) and loss power of the synthesized ferrofluids were all influenced by the substitution of Zn in the structure of magnetite. The Zn substituted magnetite nanoparticles obtained by this route showed a good stability in aqueous medium (pH 7) and hydrodynamic sizes below 100 nm and polydispersity indexes below 0.2. The calculated intrinsic loss power (ILP) for the sample x=0.3 (e.g. 2.36 nH m²/kg) was comparable to ILP of commercial ferrofluids with similar hydrodynamic sizes.     

Fabrication and characterization of magnetic Fe3O4-CNT composites

Carbon nanotubes (CNTs) decorated with magnetite nanoparticles on their external surface have been fabricated by in situ solvothermal method, which was conducted in benzene at 500 °C with ferrocene and CNTs as starting reagents. The as-prepared composites were characterized using XRD, FTIR, SEM and TEM. It has been found that the amount of magnetite nanoparticles deposited on the CNTs can be controlled by adjusting the initial mass ratio of ferrocene to CNTs. The Fe₃O₄-CNT composites display good ferromagnetic property at room temperature, with a saturation magnetization value (M_s) of 32.5 emu g⁻¹ and a coercivity (H_c) of 110 Oe.     

NMR relaxivity of coated and non-coated size-sorted maghemite nanoparticles

ABSTRACT

The effect of polymer coating on MNR relaxometry of maghemite nanoparticles has been studied. The samples were carefully sorted by size in order to reach narrow size distribution (<0.2) with size ranging from 4.5 to 12.5?nm. Relaxation dispersion profile as well as studies at a fixed Larmor frequency, were recorded for numerous either uncoated or polymer coated samples. The NMR relaxivities r₁ and r₂ increase with nanoparticle diameter. We have analysed the role of polydispersity for nanoparticles with the same mean size on the dispersion curves. We have compared the role of coating on nanoparticles NMR relaxivity between bare and poly(sodium acrylate-co-maleate) coated nanoparticles. We have investigated the influence of nanoparticle size on the T₁ and T₂ activation energy Ea. While Ea decreases with nanoparticle diameter when determined from T₁, it increases from T₂ determination. The influence is more important for small particles (<9?nm) than for big particles (>9?nm). Moreover, the PAAMA coating changes the energy Ea obtained from T₂: Ea becomes independent of the nanoparticle diameter. These results highlight the need of a complete characterisation of the role of the coating on the relaxation of magnetic particles.     

A novel non-thermal process of TiO2-shell coating on Fe3O4-core nanoparticles

In this work magnetite (Fe₃O₄) nanoparticles coated with titanium dioxide (TiO₂) were prepared by a novel non-thermal method. In this method, magnetite and pure TiO₂ (anatase) nanoparticles were individually prepared by the sol–gel method. After modifying the surface of magnetite nanoparticles by sodium citrate, titanium dioxide was coated on them without using conjunction or heat treatment to obtain Fe₃O₄:TiO₂ core–shell nanoparticles. XRD, EDX, SEM, TEM and VSM were used to investigate the structure, morphology and magnetic properties of the samples. The average crystallite size of the powders was measured by Scherrer's formula. The results obtained from different measurements confirm the formation of Fe₃O₄:TiO₂ core–shell nanoparticles with a decrease in saturation magnetization. Hysteresis loops of the core–shell nanoparticles show no exchange bias effects, which confirms that there is no interaction or interdiffusion at the interface.     

Mössbauer spectroscopy and proton relaxometry study of magnetite nanoparticles designed for preparing diagnostic contrast media

Mössbauer spectroscopy, proton relaxometry, and transmission electron microscopy are used to study magnetite nanoparticles designed for creating diagnostic contrast media. Superparamagnetic magnetite nanoparticles with a size of 5–7 nm and blocking temperature of T _b = 50 K are examined as a component of diagnostic contrast media with relaxation times T ₁ and T ₂ capable of circulating in the bloodstream for a long time. Larger ferrimagnetic nanoparticles (30–40 nm) can be concentrated in pathological tissues by applying an external magnetic field, thereby providing a means for hyperthermia.     

Study of cerium doped magnetite (Fe3O4:Ce)/PMMA nanocomposites

The paper presents the synthesis and properties of polymer nanocomposite material based on cerium doped magnetite (Fe₃O₄) as filler material and poly methyl methacrylate (PMMA) as host matrix. The magnetite (Fe₃O₄) particles were synthesized by co-precipitation route using stable ferrous and ferric salts with ammonium hydroxide as precipitating agent. Further, they doped by cerium oxide (CeO₂) non-stoichiometrically. The composite material was fabricated by solvent evaporation method. Here 2.4 GHz microwaves were used to study the effect of microwaves heating on polymerization. The phase and crystal structure is determined by X-ray diffraction (XRD). The average crystallite size of the composites varies from 28 to 35 nm. The chemical structure is confirmed by Fourier transform infrared (FTIR) spectroscopy. The magnetic and thermal properties are investigated by vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC). The thermal study shows that the microwave heated samples possess higher glass transition temperature (T_g). The magnetic results suggest that coercivity (H_C) and squareness (M_r/M_s) of the loop increases with increasing doping percent of cerium.     

HoF3 and DyF3 Nanoparticles as Contrast Agents for High‐Field Magnetic Resonance Imaging

Clinical contrast agents (CAs) currently used in magnetic resonance imaging (MRI) at low fields are less effective at high magnetic fields. The development of new CAs is mandatory to improve diagnostic capabilities of the new generation of high field MRI scanners. The purpose of this study is to synthesize uniform, water dispersible LnF₃ (Ln = Ho, Dy) nanoparticles (NPs) and to evaluate their relaxivity at high magnetic field (9.4 T) as a function of size and composition. Two different types of HoF₃ NPs are obtained by homogeneous precipitation in ethylene glycol at 120 °C. The use of holmium acetate as holmium precursor leads to rhombus‐like nanoparticles, while smaller, ellipsoid‐like nanoparticles are obtained when nitrate is used as the holmium salt. To explain this behavior, the mechanism of formation of both kinds of particles is analyzed in detail. Likewise, rhombus‐like DyF₃ nanoparticles are prepared following the same method as for the rhombus‐like HoF₃ nanoparticles. We have found, to the best of knowledge, the highest transverse relaxivity values at 9.4 T described in the literature for this kind of CAs. Finally, the LnF₃ NPs have shown negligible cytotoxicity for C6 rat glioma cells for concentrations up to 0.1 mg mL^?1.