Probing magnetic and gold nanoparticles by using MAClevers (R) as ultrasensitive sensors

Magnetic AFM probes known as MAClevers (R) were employed for sensing picogram amounts of magnetic nanoparticles, based on the cantilever frequency shifts resulting from the magnetically induced adsorption of mass. By using organothiol functionalized magnetic nanoparticles, this analytical strategy was successfully extended to the detection of gold nanoparticles, as confirmed by confocal Raman microscopy.

Experimental study of the structural, microscopy and magnetic properties of Ni-doped SnO(2) nanoparticles

A polymer precursor method has been used to synthesize Ni-doped SnO(2) nanoparticles. X-ray diffraction (XRD) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO(2)) for Ni contents below 10 mol%. In this concentration range, the particle sizes decrease with increasing Ni content and a bulk solid solution limit was determined at similar to 1 mol%. Ni surface enrichment is present at concentrations higher than the solution limit. Only above 10 mol% Ni. the formation of a second NiO-related phase has been determined. Magnetization measurements suggest the occurrence of ferromagnetism for samples in the solid solution regime (below similar to 1 mol%). This ferromagnetism is associated with the exchange interaction between electron spins trapped on oxygen vacancies, and is enhanced as the amount of Ni(2+) substituting at Sn(4+) sites increases. Above the solid solution limit, ferromagnetism is destroyed by the Ni surface enrichment and the system behaves as a paramagnet. (C) 2010 Elsevier B.V. All rights reserved.

Characterization of the Biocompatible Magnetic Colloid on the Basis of Fe(3)O(4) Nanoparticles Coated with Dextran, Used as Contrast Agent in Magnetic Resonance Imaging

The magnetic resonance imaging contrast agent, the so-called Endorem (TM) colloidal suspension on the basis of superparamagnetic iron oxide nanoparticles (mean diameter of 5.5 nm) coated with dextran, were characterized on the basis of several measurement techniques to determine the parameters of their most important physical and chemical properties. It is assumed that each nanoparticle is consisted of Fe(3)O(4) monodomain and it was observed that its oxidation to gamma-Fe(2)O(3) occurs at 253.1 degrees C. The Mossbauer spectroscopy have shown a superparamagnetic behavior of the magnetic nanoparticles. The Magnetic Resonance results show an increase of the relaxation times T(1), T(2), and T(2)* with decreasing concentration of iron oxide nanoparticles. The relaxation effects of SPIONs contrast agents are influenced by their local concentration as well as the applied field strength and the environment in which these agents interact with surrounding protons. The proton relaxation rates presented a linear behavior with concentration. The measured values of thermooptic coefficient partial derivative n/partial derivative T, thermal conductivity K, optical birefringence Delta n(0), nonlinear refractive index n(2), nonlinear absorption beta` and third-order nonlinear susceptibility vertical bar chi((3))vertical bar are also reported.

Learning form Nature to improve the heat generation of iron-oxide nanoparticles for magnetic hyperthermia applications.

The performance of magnetic nanoparticles is intimately entwined with their structure, mean size and magnetic anisotropy. Besides, ensembles offer a unique way of engineering the magnetic response by modifying the strength of the dipolar interactions between particles. Here we report on an experimental and theoretical analysis of magnetic hyperthermia, a rapidly developing technique in medical research and oncology. Experimentally, we demonstrate that single-domain cubic iron oxide particles resembling bacterial magnetosomes have superior magnetic heating efficiency compared to spherical particles of similar sizes. Monte Carlo simulations at the atomic level corroborate the larger anisotropy of the cubic particles in comparison with the spherical ones, thus evidencing the beneficial role of surface anisotropy in the improved heating power. Moreover we establish a quantitative link between the particle assembling, the interactions and the heating properties. This knowledge opens new perspectives for improved hyperthermia, an alternative to conventional cancer therapies.

Therapeutic mechanism of treating SMMC-7721 liver cancer cells with magnetic fluid hyperthermia using Fe2O3 nanoparticles

This study aimed to investigate the therapeutic mechanism of treating SMMC-7721 liver cancer cells with magnetic fluid hyperthermia (MFH) using Fe2O3 nanoparticles. Hepatocarcinoma SMMC-7721 cells cultured in vitro were treated with ferrofluid containing Fe2O3 nanoparticles and irradiated with an alternating radio frequency magnetic field. The influence of the treatment on the cells was examined by inverted microscopy, MTT and flow cytometry. To study the therapeutic mechanism of the Fe2O3 MFH, Hsp70, Bax, Bcl-2 and p53 were detected by immunocytochemistry and reverse transcription polymerase chain reaction (RT-PCR). It was shown that Fe2O3 MFH could cause cellular necrosis, induce cellular apoptosis, and significantly inhibit cellular growth, all of which appeared to be dependent on the concentration of the Fe2O3 nanoparticles. Immunocytochemistry results showed that MFH could induce high expression of Hsp70 and Bax, decrease the expression of mutant p53, and had little effect on Bcl-2. RT-PCR indicated that Hsp70 expression was high in the early stage of MFH (<24 h) and became low or absent after 24 h of MFH treatment. It can be concluded that Fe2O3 MFH significantly inhibited the proliferation of in vitro cultured liver cancer cells (SMMC-7721), induced cell apoptosis and arrested the cell cycle at the G2/M phase. Fe2O3 MFH can induce high Hsp70 expression at an early stage, enhance the expression of Bax, and decrease the expression of mutant p53, which promotes the apoptosis of tumor cells.

Magnetic characterization of ferrihydrite nanoparticles synthesized by hydrolysis of Fe metal-organic precursor

We investigate the formation of ferrihydrite nanoparticles (NPs) by hydrolysis of the Fe(III) alkoxide Fe(O(t)Bu)(3). Controlled amounts of water, up to 3.0 vol%, were added to the precursor solution yielding a series of hydrolyzed samples ranging from P0.0 (the unreacted precursor) to P3.0. X-ray diffraction (XRD) analysis evidenced the formation of high-crystalline ferrihydrite NP in sample P3.0, with grain size estimate of about 3.2 nm. The transition from the molecular precursor to the formation of crystalline magnetic NPs was followed through magnetization measurements M(T) and M(H), as well as Mossbauer spectroscopy (MS). M(T) measurements indicate a paramagnetic (PM) behavior for sample P0.0, characteristic of binuclear Fe-O-Fe units, which evolves to a superparamagnetic (SPM) behavior, with an energy barrier for the blocking process estimated for sample P3.0 as E(a) = 4.9 x 10(-21) J (E(a)/k(B) = 355 K), resulting in a high effective anisotropy constant K(eff) = 290 kJ/m(3). Magnetization loops at 5 K progressively change from PM-like to ferromagnetic-like shape upon increasing the hydrolysis process, although hysteresis (H(c) approximate to 500 Oe) only is apparent for P2.0 and higher. MS spectra at room temperature are PM/SPM doublets for all samples, while the MS spectra at T = 4.2 K reveal increasingly well-defined magnetic ordering as hydrolysis of the precursor stepwise progresses until well-crystallized ferrihydrite particles are formed. (C) 2008 Elsevier B.V. All rights reserved.

Magnetic Hyperthermia With Fe(3)O(4) Nanoparticles: The Influence of Particle Size on Energy Absorption

We have studied the magnetic and power absorption properties of a series of magnetic nanoparticles (MNPs) of Fe(3)O(4) with average sizes < d > ranging from 3 to 26 rim. Heating experiments as a function of particle size revealed a strong increase in the specific power absorption (SPA) values for particles with < d > = 25-30 mn. On the other side saturation magnetization M(s) values of these MNPs remain essentially constant for particles with < d > above 10 rim, suggesting that the absorption mechanism is not determined by Ms. The largest SPA value obtained was 130 W/g, corresponding to a bimodal particle distribution with average size values of 17 and 26 nm.

Iron Oxide Versus Fe55Pt45/Fe3O4: Improved Magnetic Properties of Core/Shell Nanoparticles for Biomedical Applications

In this paper, synthesis of the Fe55Pt45/Fe3O4 core/shell structured nanoparticles using the modified polyol process combined with the seed-mediated growth method is reported. Iron oxide shell thickness was tuned controlling the Fe(acac)(3)/FePt seeds in the reaction medium. Annealing of the core/shell structure leads to iron-rich layer formation around the hard FePt phase in the nanoparticle core. However, the 2 nm Fe3O4 shell thickness seems to be the limit to obtain the enhanced magnetization close to the alpha-Fe and preserving an iron oxide shell after annealing at 500 degrees C for 30 min in a reducing atmosphere. The presence of both the oxide layer on nanoparticle surface and an intermediate iron-rich FePt layer after annealing promote strong decreases in the coercive field of the 2-nm-oxide shell thickness. These annealed nanoparticles were functionalized with dextran, presenting the enhanced characteristics for biomedical applications such as higher magnetization, very low coercivity, and a slightly iron oxide passivated layer, which leads an easy functionalization and decreases the nanoparticle toxicity.

Magnetic properties of acicular Fe1-xREx (RE = Nd, Sm, Eu, Tb; x=0, 0.05, 0.10) metallic nanoparticles

Acicular monodispersed Fe1-xREx (RE= Nd, Sm,Eu,Tb;x=0, 0.05, 0.10) metallic nanoparticles (60 +/- 5 nm in length and axial ratio similar to6) obtained by reduction of alumina-coated goethite nanoparticles-containing rare earth (RE) under hydrogen flow are reported. Alumina and maghemite thin layers on particle surface were used to protect the goethite particles against sintering and oxidation, respectively. Al and RE additions were obtained by successive heterocoagulation reactions. Aluminum sulfate (10 at.% based on Fe) was dissolved in water and the pH adjusted to 12.5 with NaOH solution. Goethite particles were suspended in this solution and CO2 gas was blown into the slurry to neutralize it to a pH 8.5 or less. Particles were purified and dehydrated to effect transformation to alumina-coated hematite nanoparticles, which were re-suspended in aqueous solution in which RE sulfate (0-0.15 at.% based on Fe) has been dissolved, and the pH increased by ammonia aqueous solution addition. Resulted alumina-coated RE-doped hematite nanoparticles were reduced to metal at 450 degreesC/12 h under hydrogen flow and passivated with nitrogen-containing ethanol vapor at room temperature. Acicular monodispersed metallic nanoparticle systems were obtained and the presence of Al and RE were confirmed by induced-coupled plasma spectrometry analysis. X-ray diffraction, Mossbauer spectroscopy, and magnetization data are in agreement with the nanosized alpha-Fe core in a bcc structure, having a spinel structure, gammaFe(2)O(3), with thickness similar to1.5 run on particle surface. Main magnetic parameters showed saturation magnetization decreases and significant increasing in the coercive field with the RE composition increases. Magnetic properties of these particles, similar to40% smaller than those commercially available, suggest a decrease in the bit-size for high-density magnetic or magneto-optics recording media application. (C) 2004 Published by Elsevier B.V.

Magnetic Purification of Curcumin from Curcuma longa Rhizome by Novel Naked Maghemite Nanoparticles

Naked maghemite nanoparticles, namely, surface active maghemite nanoparticles (SAMNs), characterized by a diameter of about 10 nm, possessing peculiar colloidal stability, surface chemistry, and superparamagnetism, present fundamental requisites for the development of effective magnetic purification processes for biomolecules in complex matrices. Polyphenolic molecules presenting functionalities with different proclivities toward iron chelation were studied as probes for testing SAMN suitability for magnetic purification. Thus, the binding efficiency and reversibility on SAMNs of phenolic compounds of interest in the pharmaceutical and food industries, namely, catechin, tyrosine, hydroxytyrosine, ferulic acid, coumaric acid, rosmarinic acid, naringenin, curcumin, and cyanidin-3-glucoside, were evaluated. Curcumin emerged as an elective compound, suitable for magnetic purification by SAMNs from complex matrices. A combination of curcumin, demethoxycurcumin, and bis-demethoxycurcumin was recovered by a single magnetic purification step from extracts of Curcuma longa rhizomes, with a purity >98% and a purification yield of 45%, curcumin being >80% of the total purified curcuminoids.

Magnetic nanohydrometallurgy: A promising nanotechnological approach for metal production and recovery using functionalized superparamagnetic nanoparticles

We report on a new, promising nanotechnological approach for hydrometallurgy based on recyclable, chemically functionalized superparamagnetic nanoparticles. In this process, the metal ions (e.g. Cu2+) are captured by the nanoparticles and confined at the electrode surface by means of an external magnet. Due to the pre-concentration effect the electrodeposition process is greatly improved, yielding the pure metal in a much shorter time in comparison with the conventional electrodeposition process. After the electrolysis, the magnetic nanoparticles are ready to return to the process. The proposed strategy can advantageously be incorporated in hydrometallurgy, reducing the number of steps associated with complexation, organic solvent extraction, metal release and diffusional electroprocessing, leading to a more sustainable technology. (C) 2012 Elsevier B.V. All rights reserved.

Stimuli-responsive magnetic particles for biomedical applications

In recent years, magnetic nanoparticles have been studied due to their potential applications as magnetic carriers in biomedical area. These materials have been increasingly exploited as efficient delivery vectors, leading to opportunities of use as magnetic resonance imaging (MRI) agents, mediators of hyperthermia cancer treatment and in targeted therapies. Much attention has been also focused on ""smart"" polymers, which are able to respond to environmental changes, such as changes in the temperature and pH. In this context, this article reviews the state-of-the art in stimuli-responsive magnetic systems for biomedical applications. The paper describes different types of stimuli-sensitive systems, mainly temperature- and pH sensitive polymers, the combination of this characteristic with magnetic properties and, finally, it gives an account of their preparation methods. The article also discusses the main in vivo biomedical applications of such materials. A survey of the recent literature on various stimuli-responsive magnetic gels in biomedical applications is also included. (C) 2010 Elsevier B.V. All rights reserved.

Preparation, characterization and in vitro cytotoxicity of BSA-based nanospheres containing nanosized magnetic particles and/or photosensitizer

This study reports on the preparation, characterization and in vitro toxicity test of a new nano-drug delivery system (NDDS) based on bovine serum albumin (BSA) nanospheres which incorporates surface-functionalized magnetic nanoparticles (MNP) and/or the silicon(IV) phthalocyanine (NzPc). The new NDDS was engineered for use in photodynamic therapy (PDT) combined with hyperthermia (HPT) to address cancer treatment. The BSA-based nanospheres, hosting NzPc, MNP or both (NzPc and MNP), present spherical shape with hydrodynamic average diameter values ranging from 170 to 450 nm and zeta potential of around -23 mV. No difference on the fluorescence spectrum of the encapsulated NzPc was found regardless of the presence of MNP. Time-dependent fluorescence measurements of the encapsulated NzPc revealed a bi-exponential decay for samples incorporating only NzPc and NzPc plus MNP, in the time window ranging from 1.70 to 5.20 ns. The in vitro assay, using human fibroblasts, revealed no cytotoxic effect in all samples investigated, demonstrating the potential of the tested system as a synergistic NDDS. (C) 2009 Elsevier B.V. All rights reserved.

Dynamic susceptibility investigation of maghemite nanoparticles incorporated in bovine serum albumin template

Room-temperature measurements of the magnetic susceptibility of Bovine Serum Albumin-based nanocapsules (50 to 300 nm in size) loaded with different amounts of maghemite nanoparticles (7.6 nm average diameter) have been carried out in this study The field (H) dependence of the imaginary peak susceptibility (f(P)) of the nanocomposite samples was investigated in the range of 0 to 4 kOe. From the analysis of the f(P) x H curves the concentration (N) dependence of the effective maghemite magnetocrystalline energy barrier (E) was obtained. Analysis of the E x N data was performed using a modified Morup-Tronc [Phys. Rev. Lett. 72, 3278 (1994)] model, from which a huge contribution from the magnetocrystalline surface anisotropy was observed.

Kinetics of elimination and distribution in blood and liver of biocompatible ferrofluids based on Fe(3)O(4) nanoparticles: An EPR and XRF study

In this study, we evaluated the biodistribution and the elimination kinetics of a biocompatible magnetic fluid, Endorem (TM), based on dextrancoated Fe(3)O(4) nanoparticles endovenously injected into Winstar rats. The iron content in blood and liver samples was recorded using electron paramagnetic resonance (EPR) and X-ray fluorescence (XRF) techniques. The EPR line intensity at g=2.1 was found to be proportional to the concentration of magnetic nanoparticles and the best temperature for spectra acquisition was 298 K. Both EPR and XRF analysis indicated that the maximum concentration of iron in the liver occurred 95 min after the ferrofluid administration. The half-life of the magnetic nanoparticles (MNP) in the blood was (11.6 +/- 0.6) min measured by EPR and (12.6 +/- 0.6) min determined by XRF. These results indicate that both EPR and XRF are very useful and appropriate techniques for the study of kinetics of ferrofluid elimination and biodistribution after its administration into the organism. (c) 2007 Elsevier B.V. All rights reserved.