ABSTRACT: Finally, we have addressed some relevant findings on the importance of having well-defined synthetic strategies developed for the generation of MNPs, with a focus on particle formation mechanism and recent modifications made on the preparation of monodisperse samples of relatively large quantities not only with similar physical features, but also with similar crystallochemical characteristics. Then, different methodologies for the functionalization of the prepared MNPs together with the characterization techniques are explained. Theorical views on the magnetism of nanoparticles are considered.

Functionalization of iron oxide nanoparticles with quaternary ammonium ion-based aminooxy and oxime ether substrates provides a flexible route for generating magnetic gene delivery vectors. Using the MCF-7 breast cancer cell line, our findings show that pDNA magnetoplexes derived from the lipid-coated nanoparticle formulation dMLP transfect in the presence of 10% serum with or without magnetic assistance at significantly higher levels than a commonly used cationic liposome formulation, based on luciferase assay. The present ion-pairing, click chemistry approach furnishes Fe(3)O(4) nanoparticles with lipid layers. The resultant magnetic nanovectors serve as transfection enhancers for otherwise transfection-inactive materials.

Gold nanoshell around super paramagnetic iron oxide nanoparticles (SPIONs) was synthesized and small angle X-ray scattering (SAXS) analysis suggests a gold coating of approximately 0.4 to 0.5 nm thickness. On application of low frequency oscillating magnetic fields (44 - 430 Hz), a four- to five-fold increase in the amount of heat released with gold-coated SPIONs (6.3 nm size) in comparison with SPIONs (5.4 nm size) was observed. Details of the influence of frequencies of oscillating magnetic field, concentration and solvent on heat generation are presented. We also show that, in the absence of oscillating magnetic field, both SPIONs and SPIONs@Au are not particularly cytotoxic to mammalian cells (MCF-7 breast carcinoma cells and H9c2 cardiomyoblasts) in culture, as indicated by the reduction of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium by viable cells in a phenazine methosulfate-assisted reaction.

This study intended to prepare iron oxide nanoparticle-entrapped chitosan (CS) nanoparticles for stem cell labeling. The nanoparticles were synthesized by polymerizing iron oxide nanoparticle-associated methacrylic acid monomer in the presence of CS. TEM revealed that the well-defined iron oxide nanoparticles were successfully encapsulated inside the CS nanoparticles. The effect of CS at different [NH(2)]/[COOH] molar ratios on particle size, surface charge, thermal stability and magnetic properties was determined systematically. Internalization and localization of the coated nanoparticles were evaluated by atomic absorption spectrometry and confocal laser scanning microscopy. The Kusa O cell line was chosen as a stem cell model. Interestingly, the uptake of iron oxide-entrapped CS nanoparticles was remarkably enhanced under magnetization and the nanoparticles were mostly located inside cellular compartments. It can be concluded that the iron oxide-entrapped CS nanoparticles have a strong potential for stem cell labeling.

In this study, superparamagnetic monodisperse magnetite colloids, around 5nm in size, were prepared by dissolving iron chlorides, sodium hydroxide (NaOH) and sodium oleate (NaOL), in toluene/ethanol/water mixtures and refluxing for 4h. The concentrations of NaOH and NaOL were varied to systematically investigate the effect on the surface properties, size, dispersion, and magnetic properties of magnetite nanoparticles (MNPs). The samples were characterized via XRD, FTIR, TGA, TEM, SAED, DLS, and VSM. The results indicated that the surface coatings of MNPs could be manipulated from oleate to hydroxyl groups via increasing the molar ratio of NaOH/Fe(II) more than 8. The amount of NaOH had no obvious influence on the size and the saturation magnetization of MNPs. Therefore NaOH was not a necessary reactant for forming magnetite crystals. On the contrary, NaOL was shown to be the most important component for synthesizing stable magnetite colloids. The NaOL acted as both a key reactant to buffer the pH environment and a surfactant to keep the MNPs stable in nonpolar solvent media.

In a magnetofection procedure, self-assembling complexes of enhancers like cationic lipids with plasmid DNA or small interfering RNA (siRNA) are associated with magnetic nanoparticles and are then concentrated at the surface of cultured cells by applying a permanent inhomogeneous magnetic field. This process results in a considerable improvement in transfection efficiency compared to transfection carried out with nonmagnetic gene vectors. This article describes how to synthesize magnetic nanoparticles suitable for nucleic acid delivery by liposomal magnetofection and how to test the plasmid DNA and siRNA association with the magnetic components of the transfection complex. Protocols are provided for preparing magnetic lipoplexes, performing magnetofection in adherent and suspension cells, estimating the association/internalization of vectors with cells, performing reporter gene analysis, and assessing cell viability. The methods described here can be used to screen magnetic nanoparticles and formulations for the delivery of nucleic acids by liposomal magnetofection in any cell type.

Advances in nanotechnology have pushed forward the synthesis of a variety of functional nanoparticles (NPs) such as semiconductor quantum dots (QDs), magnetic and metallic NPs. The unique electronic, magnetic, and optical properties exhibited by these nanometer-sized materials have enabled a broad spectrum of biomedical applications. In particular, iron-oxide-based magnetic NPs have proved to be highly versatile deep-tissue imaging agents, having been incorporated into clinical applications due to their biocompatibility. This Interdisciplinary Review will focus on the recent advances in strategies for the synthesis and surface modification of highly monodisperse magnetic NPs and their use in imaging, drug delivery, and innovative ultrasensitive bioassays.

Superparamagnetic iron oxide nanoparticles can be used for numerous applications such as MRI contrast enhancement, hyperthermia, detoxification of biological fluids, drug delivery, or cell separation. In this work, we will summarize the chemical routes for synthesis of iron oxide nanoparticles, the fluid stabilization, and the surface modification of superparamagnetic iron oxide nanoparticles. Some examples of the numerous applications of these particles in the biomedical field mainly as MRI negative contrast agents for tissue-specific imaging, cellular labeling, and molecular imaging will be given. Larger particles or particles displaying a non-neutral surface (thanks to their coating or to a cell transfection agent with which they are mixed) are very useful tools, although the cells to be labeled have no professional phagocytic function. Labeled cells can then be transplanted and monitored by MRI in a broad spectrum of applications. Direct in vivo magnetic labeling of cells is mainly performed by intravenous injection of long-circulating iron oxide-based MRI contrast agents, which can extravasate and/or undergo a cellular uptake in an amount sufficient to allow an MRI visualization of areas of interest such as inflamed regions or tumors. Particles with long circulation times, or able to induce a strong negative effect individually have been also modified by conjugation to a ligand, so that their cellular uptake, or at least their binding to the cell surface, could occur through a specific ligand-receptor interaction, in vivo as well as in vitro. Thus, experimentally as well as in a few trials on humans, iron oxide particles currently find promising applications.

The grafting of pegylated dendrons on 9(2) nm and 39(5) nm iron oxide nanoparticles in water, through a phosphonate group as coupling agent has been successfully achieved and its mechanism investigated, with a view to produce biocompatible magnetic nano-objects for biomedical applications. Grafting has been demonstrated to occur by interaction of negatively charged phosphonate groups with positively charged groups and hydroxyl at the iron oxide surface. The isoelectric point of the suspension of dendronized iron oxide nanoparticles is shifted towards lower pH as the amount of dendron increases. It reaches 4.7 for the higher grafting rate and for both particle size. Thus, the grafting of molecules using a phosphonate group allows stabilizing electrostatically the suspensions at physiological pH, a prerequisite for biomedical applications. Moreover the grafting step has been shown to preserve the magnetic properties of iron oxide nanoparticles due to super-super exchange interactions through the phosphonate group.

A novel method for control burst releasing of drug via a high frequency magnetic field (HFMF) from magnetic-sensitive silica nanospheres was developed. The nanospheres were synthesized by a combination of emulsion and sol-gel process with the particles controlled at about 80 nm in diameter. Under repeated exposures to the high frequency magnetic stimulus, the drug release behaviors showed reproducible slow-to-burst profiles while consecutively applying the magnetic stimulus at 10-min switching time and the release profile restored immediately when the stimulus was removed. By taking this non-contact control-burst method, the magnetic silica nanospheres can be designed to treat the cancer therapy and urgent physiological needs.

This article provides an up-to-date review on nanocomposites composed of inorganic nanoparticles and the polymer matrix for optical and magnetic applications. Optical or magnetic characteristics can change upon the decrease of particle sizes to very small dimensions, which are, in general, of major interest in the area of nanocomposite materials. The use of inorganic nanoparticles into the polymer matrix can provide high-performance novel materials that find applications in many industrial fields. With this respect, frequently considered features are optical properties such as light absorption (UV and color), and the extent of light scattering or, in the case of metal particles, photoluminescence, dichroism, and so on, and magnetic properties such as superparamagnetism, electromagnetic wave absorption, and electromagnetic interference shielding. A general introduction, definition, and historical development of polymer-inorganic nanocomposites as well as a comprehensive review of synthetic techniques for polymer-inorganic nanocomposites will be given. Future possibilities for the development of nanocomposites for optical and magnetic applications are also introduced. It is expected that the use of new functional inorganic nano-fillers will lead to new polymer-inorganic nanocomposites with unique combinations of material properties. By careful selection of synthetic techniques and understanding/exploiting the unique physics of the polymeric nanocomposites in such materials, novel functional polymer-inorganic nanocomposites can be designed and fabricated for new interesting applications such as optoelectronic and magneto-optic applications.

PMMA/Fe-oxide nanocomposites are fabricated by a chemical method. Monodispersed Fe-oxide nanoparticles are well dispersed in the PMMA matrix by in situ polymerization, resulting in a bulk transparent polymeric nanocomposite. The magnetic behavior of the PMMA/Fe-oxide nanocomposites is investigated. The transparent PMMA/Fe-oxide nanocomposite has potentially interesting magneto-optic applications without compromising the advantages of a lightweight, noncorrosive polymeric material with very high transparency even for bulk samples.

In this paper, the positive effect of a gold layer on cell viability is demonstrated by examining the results given by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfop henyl)-2H-tetrazolium (MTS) assay and two-color cell fluorescence viability (TCCV) assay. These cytotoxicity tests were performed with human cervical adenocarcinoma cells (HeLa cell line) and transformed African green monkey kidney fibroblast cells (Cos-7 cell line). To fabricate the nanostructures as drug vehicles, first, poly(l,l-lactide-co-ethylene glycol)(PLLA-PEG) and poly(N-isopropylacrylamide-co-D,D-lactide)(PNIPAAm-PDLA) were synthesized, and then two kinds of thermosensitive nanospheres comprising "shell-in-shell" structures without a gold layer (PLLA-PEG@PNIPAAm-PDLA) and with a gold layer (Au@PLLA-PEG@PNIPAAm-PDLA) were constructed by a modified double-emulsion method (MDEM). Both of them displayed a unique thermosensitive character exhibiting the lower critical solubility temperature (LCST) at 36.7 degrees C which was confirmed by UV-vis spectroscopy and differential scanning calorimetry (DSC). The release profiles of entrapped bovine serum albumin (BSA) were monitored at 22 and 37 degrees C, respectively, to reveal the thermal dependence on the release rate. In cell viability tests, both PLLA-PEG@PNIPAAm-PDLA and Au@PLLA-PEG@PNIPAAm-PDLA showed excellent cell viability, and furthermore, Au@PLLA-PEG@PNIPAAm-PDLA, particularly at high doses, exhibited more enhanced cell viability than PLLA-PEG@PNIPAAm-PDLA. This effect is mainly attributed to the gold layer which binds the protein molecules first and consequently facilitates transmembrane uptake of essential nutrients in the cell media, resulting in favorable cell proliferation.

A nanocomposite generator (NCG) is fabricated using piezoelectric BaTiO(3) nanoparticles and universal graphitic carbons (carbon nanotubes and reduced graphene oxide). A piezoelectric nanocomposite is produced by the simple process of dispersing nanoparticles and carbon-based nanomaterials in a polydimethylsiloxane matrix and subsequent spin-casting onto a metal-coated plastic substrate. The NCG device generates an output voltage of ∼3.2 V and a current of ∼350 nA under periodic mechanical deformation to a strain of 0.33%. The generated electric energy is stored in capacitors and used to light up a commercial light-emitting diode.

The application of surface modified magnetic adsorbent particles in combination with magnetic separation techniques has received considerable awareness in recent years. There is a particular need in protein purification and analysis for specific, functional and generic methods of protein binding on solid supports. Nanoscale superparamagnetic iron oxide particles have been used to purify a natural coagulant protein extracted from Moringa oleifera seeds. Spectrophotometric analysis of the coagulant protein was performed using synthetic clay solution as substrate. Protein binding with carboxyl and silica surface modified superparamagnetic iron oxide nanoparticles (SPION) were compared with the known carboxyl methyl cellulose (CMC) beads of approximately 1 microm. SPION modified with carboxyl surface showed higher binding capacity towards the coagulant protein compared to the CMC beads. The high surface area to volume ratio of the carboxyl-coated SPION resulted in high binding capacity and rapid adsorption kinetics of the crude protein extract. The purification and molecular weight of coagulant protein is analyzed by SDS-PAGE. This approach utilizes the most efficient, feasible and economical method of coagulant protein purification and it can also be applicable to other proteins that possess similar properties.

A 48 year old woman was diagnosed with a huge cystic mass in her abdominal cavity. She complained of significant abdominal discomfort due to the mass. The abdominal computed tomography revealed a giant multi-lobulated mass, measuring 26×12 cm in size, adjacent to the lesser curvature of the stomach. In the operation field, the mass was found to originate from the lesser omentum, including the right and left gastric vessels and the vagus nerves, and to invade the lesser curvature of the stomach. For curative resection, distal subtotal gastrectomy with mass excision followed by gastroduodenostomy were performed. This mass was pathologically diagnosed to be a mesenteric cystic lymphangioma; in fact, the largest ever reported. The patient had no complications during the postoperative period and was discharged from the hospital on the seventh day after surgery.

Microsomal glutathione transferase 1 (MGST1) is an antioxidant enzyme located predominantly in the mitochondrial outer membrane and endoplasmic reticulum and has been shown to protect cells from lipid peroxidation induced by a variety of cytostatic drugs and pro-oxidant stimuli. We hypothesized that MGST1 may also protect against nanomaterial-induced cytotoxicity through a specific effect on lipid peroxidation. We evaluated the induction of cytotoxicity and oxidative stress by TiO(2), CeO(2), SiO(2), and ZnO in the human MCF-7 cell line with or without overexpression of MGST1. SiO(2) and ZnO nanoparticles caused dose- and time-dependent toxicity, whereas no obvious cytotoxic effects were induced by nanoparticles of TiO(2) and CeO(2). We also noted pronounced cytotoxicity for three out of four additional SiO(2) nanoparticles tested. Overexpression of MGST1 reversed the cytotoxicity of the main SiO(2) nanoparticles tested and for one of the supplementary SiO(2) nanoparticles but did not protect cells against ZnO-induced cytotoxic effects. The data point toward a role of lipid peroxidation in SiO(2) nanoparticle-induced cell death. For ZnO nanoparticles, rapid dissolution was observed, and the subsequent interaction of Zn(2+) with cellular targets is likely to contribute to the cytotoxic effects. A direct inhibition of MGST1 by Zn(2+) could provide a possible explanation for the lack of protection against ZnO nanoparticles in this model. Our data also showed that SiO(2) nanoparticle-induced cytotoxicity is mitigated in the presence of serum, potentially through masking of reactive surface groups by serum proteins, whereas ZnO nanoparticles were cytotoxic both in the presence and in the absence of serum.

We report the lasing performance and photobleaching of gain material containing a water solution of Rhodamine 6G dye and gold nanoparticles (NPs). In comparison to a pure dye solution, the investigated material demonstrated both enhancement and quenching of the lasing output, depending on the relative concentration of the gold NPs. Although the presence of NPs with an optimized concentration looks preferable in terms of the lasing output enhancement, such additives deteriorate the operational resource of the gain material; i.e., the photobleaching rate speeds up.

Iron oxide-based nanomagnets have attracted a great deal of attention in nanomedicine over the past decade. Down to the nanoscale, superparamagnetic iron oxide nanoparticles can only be magnetized in the presence of an external magnetic field, which makes them capable of forming stable colloids in a physio-biological medium. Their superparamagnetic property, together with other intrinsic properties, such as low cytotoxicity, colloidal stability, and bioactive molecule conjugation capability, makes such nanomagnets ideal in both in-vitro and in-vivo biomedical applications. In this review, a chemical, physical, and biological synthetic approach to prepare iron oxide-based nanomagnets with different physicochemical properties was illustrated and compared. The growing interest in iron oxide-based nanomagnets with multifunctionalities was explored in cancer diagnostics and treatment, focusing on their combined roles in a magnetic resonance contrast agent, hyperthermia, and magnetic force assisted drug delivery. Iron oxides as magnetic carriers in gene therapy were reviewed with a focus on the sophisticated design and construction of magnetic vectors. Finally, the iron oxide-based nanomagnet also represents a very promising tool in particle/cell interfacing in controlling cellular functionalities, such as adhesion, proliferation, differentiation, and cell patterning, in stem cell therapy and tissue engineering applications.

Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.

Iron oxide nanoparticles, probably magnetite, as-prepared and dispersed in Copaiba oil were studied by Mössbauer spectroscopy using two different spectrometers: with a low velocity resolution (512 channels) for measurements at 295 and 21K and with a high velocity resolution (4096 channels) for measurements at 295 and 90K. The fitting of all measured spectra demonstrated that usual models applied to fit Mössbauer spectra of magnetite and maghemite particles were not suitable. Therefore, the recorded spectra were fitted using a large number of spectral components on the basis of better quality of the fit and linearity of differential spectra. The number of components obtained for the better fit appeared to be different for spectra measured with a low and a high velocity resolution. However, these results demonstrated differences of Mössbauer parameters for iron oxide nanoparticles as-prepared and dispersed in Copaiba oil at applied temperatures. The effect of Copaiba oil molecules on Mössbauer parameters may be a result of the interactions of polar molecules such as kaurinic acid with nanoparticles' surface.

Magnetic nanoparticles (MNPs) are considered highly useful in therapeutic and diagnostic applications. However, MNPs require surface modification to promote dispersibility in aqueous solutions and thus biocompatibility. In this article, the authors modified MNPs with inorganic silica layer to create silica-coated magnetite nanoparticles (MNP@Si) via sol-gel process. Synthesis involves hydrolysis and condensation steps using tetraethylorthosilicate (TEOS) in methanol/ polyethylene glycol (PEG) solution and ammonia catalyst. Nanoparticles were characterized in terms of morphology, particle size, crystalline phase, chemical-bond structure, surface charge and magnetic properties: in particular, the MNP@Si size was easily tunable through alteration of the Fe(3) O(4)-to-TEOS ratio. As this ratio increased, the MNP@Si size decreased from 270 to 15 nm whilst maintaining core 12-nm MNP particle size, indicating decrease in thickness of the silica coating. All MNP@Si, in direct contrast to uncoated MNPs, showed excellent stability in aqueous solution. The particles' physicochemical and magnetic properties systematically varied with size (coating thickness), and the zeta potential diminished toward negative values, while magnetization increased as the coating thickness decreased. 15-nm MNP@Si showed excellent magnetization (about 64.1 emu/g), almost comparable to that of uncoated MNPs (70.8 emu/g). Preliminary in vitro assays confirmed that the silica layer significantly reduced cellular toxicity as assessed by increase in cell viability and reduction in reactive oxygen species production during 48 h of culture. Newly-developed MNP@Si, with a high capacity for magnetization, water-dispersibility, and diminished cell toxicity, may be potentially useful in diverse biomedical applications, including delivery of therapeutic and diagnostic biomolecules. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2012.

The structural and magnetic properties and spin dynamics of dextran coated and uncoated γ-Fe(2)O(3)(maghemite) nanoparticles have been investigated using high resolution transmission electron microscopy (HRTEM),(57)Fe nuclear magnetic resonance (NMR), Mössbauer spectroscopy and dc magnetization measurements. The HRTEM observations indicated a well-crystallized system of ellipsoid-shaped nanoparticles, with an average size of 10 nm. The combined Mössbauer and magnetic study suggested the existence of significant interparticle interactions not only in the uncoated but also in the dextran coated nanoparticle assemblies. The zero-field NMR spectra of the nanoparticles at low temperatures are very similar to those of the bulk material, indicating the same hyperfine field values at saturation in accord with the performed Mössbauer measurements. The T(2) NMR spin-spin relaxation time of the nanoparticles has also been measured as a function of temperature and found to be two orders of magnitude shorter than that of the bulk material. It is shown that the thermal fluctuations in the longitudinal magnetization of the nanoparticles in the low temperature limit may account for the shortening and the temperature dependence of the T(2) relaxation time. Thus, the low temperature NMR results are in accord with the mechanism of collective magnetic excitations, due to the precession of the magnetization around the easy direction of the magnetization at an energy minimum, a mechanism originally proposed to interpret Mössbauer experiments in magnetic nanoparticles. The effect of the surface spins on the NMR relaxation mechanisms is also discussed.

Magnetic nanoparticle (MNP) modified by carboxymethyl dextran (CMD) was synthesized and characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, superconducting quantum interference device, dynamic light-scattering, thermogravimetric analysis, and X-ray diffraction. CMD coating on the particle surface provides abundant -COOH functional groups for conjugating with a thrombolytic drug, recombinant tissue plasminogen activator (rtPA). CMD-coated MNP (CMD-MNP) prepared with higher CMD/MNP ratios had higher CMD content, less iron content, more -COOH surface groups, smaller hydrodynamic diameter, and smaller saturation magnetization. The in vitro biocompatibility study using lactate dehydrogenase assays indicated that CMD-MNP elicited no cell cytotoxicity. The optimum drug loading could be achieved by contacting 0.25 mg rtPA with 5 mg CMD-MNP where all rtPA is immobilized to the magnetic nanocarrier with full retention of its thrombolytic activity.

For the development of a surgical mesh implant that is visible in magnetic resonance imaging (MRI), superparamagnetic iron oxides (SPIOs) are integrated into the material of the mesh. In order to get a high quality mesh regarding both mechanical and imaging properties, a narrow size distribution and homogenous spatial distribution, as well as a strong magnetization of SPIOs within the filament of the mesh are required. In this work, six different samples of SPIOs composed of a magnetite core are synthesized with and without stabilizing dodecanoic acid and analyzed using a superconducting quantum interference device (SQUID), transmission electron microscope (TEM) and a magnetic force microscope (MFM) to determine the properties that are beneficial for the assembly and imaging of the implant. These analyses show the feasibility of visualization of surgical implants with incorporated SPIOs and the influence of the agglomeration of SPIOs on their magnetization and on a homogenous spatial distribution within the polymer of the mesh.

We present the first results of electron magnetic resonance (EMR) and Mössbauer spectroscopy studies of γ-Fe(2)O(3) nanoparticles (NPs) incorporated into liquid-crystalline, second-generation dendrimers. The mean size of NPs formed in the dendrimers was around 2.5 nm. A temperature-driven transition from superparamagnetic to ferrimagnetic resonance was observed for the sample. Low-temperature blocking of the NP magnetic moments has been clearly evidenced in the integrated EMR line intensity and the blocking temperature was about 60 K. The physical parameters of magnetic NPs (magnetic moment, effective magnetic anisotropy) have been determined from analyses of the EMR data. The effective magnetic anisotropy constant is enhanced relative to bulk γ-Fe(2)O(3) and this enhanced value is associated with the influence of the surface and shape effects. The angular dependence of the EMR signal position for the field-freezing sample from liquid-crystalline phase showed that NPs possessed uniaxial anisotropy, in contrast to bulk γ-Fe(2)O(3). Mössbauer spectroscopy determined that fabricated NPs consisted of an α-Fe core and a γ-Fe(2)O(3) shell.

This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60 nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (∼10 nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives-a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pK(a) value of 6.8. The fluorescence intensity of the reference dye did not change significantly (∼3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.

Streptococcus suis Dpr belongs to the Dps family of bacterial and archaeal proteins that oxidize Fe(2+) to Fe(3+) to protect microorganisms from oxidative damage. The oxidized iron is subsequently deposited as ferrihydrite inside a protein cavity, resulting in the formation of an iron core. The size and the magnetic properties of the iron core have attracted considerable attention for nanotechnological applications in recent years. Here, the magnetic and structural properties of the iron core in wild-type Dpr and four cavity mutants were studied. All samples clearly demonstrated a superparamagnetic behavior in superconducting quantum interference device magnetometry and Mössbauer spectroscopy compatible with that of superparamagnetic ferrihydrite nanoparticles. However, all the mutants exhibited higher magnetic moments than the wild-type protein. Furthermore, measurement of the iron content with inductively coupled plasma mass spectrometry revealed a smaller amount of iron in the iron cores of the mutants, suggesting that the mutations affect nucleation and iron deposition inside the cavity. The X-ray crystal structures of the mutants revealed no changes compared with the wild-type crystal structure; thus, the differences in the magnetic moments could not be attributed to structural changes in the protein. Extended X-ray absorption fine structure measurements showed that the coordination geometry of the iron cores of the mutants was similar to that of the wild-type protein. Taken together, these results suggest that mutation of the residues that surround the iron storage cavity could be exploited to selectively modify the magnetic properties of the iron core without affecting the structure of the protein and the geometry of the iron core.

Freely suspended nanocomposite thin films based on soft polymers and functional nanostructures have been widely investigated for their potential application as active elements in microdevices. However, most studies are focused on the preparation of nanofilms composed of polyelectrolytes and charged colloidal particles. Here, a new technique for the preparation of poly(l-lactic acid) free-standing nanofilms embeddidng superparamagnetic iron oxide nanoparticles is presented. The fabrication process, based on a spin-coating deposition approach, is described, and the influence of each production parameter on the morphology and magnetic properties of the final structure is investigated. Superparamagnetic free-standing nanofilms were obtained, as evidenced by a magnetization hysteresis measurement performed with a superconducting quantum interference device (SQUID). Nanofilm surface morphology and thickness were evaluated by atomic force microscopy (AFM), and the nanoparticle dispersion inside the composites was investigated by transmission electron microscopy (TEM). These nanofilms, composed of a biodegradable polyester and remotely controllable by external magnetic fields, are promising candidates for many potential applications in the biomedical field.

In this paper, we report single step synthesis of hydrophilic superparamagnetic magnetite nanoparticles by thermolysis of Fe(acac)3 and their characterization of the properties relevant to biomedical applications like hyperthermia and magnetic resonance imaging (MRI). Size and morphology of the particles were determined by Transmission electron microscopy (TEM) while phase purity and structure of the particles were identified by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Magnetic properties were evaluated using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The as prepared nanoparticles were found to be superparamagnetic with the blocking temperature of 136 K and were easily suspendable in water. Cytotoxicity studies on human cervical (SiHa), mouse melanoma (B16F10) and mouse primary fibroblast cells demonstrated that up to a dose of 0.1 mg/ml, the magnetite nanoparticles were nontoxic to the cells. To evaluate the feasibility of their uses in hyperthermia and MRI applications, specific absorption rate (SAR) and spin-spin relaxation time (T2) were measured respectively. SAR has been calculated to be above 80 Watt/g for samples with the iron concentration of 5-20 mg/ml at 10 kA/m AC magnetic field and 425 kHz frequency. r2 relaxivity value was measured as 358.4 mM(-1)S(-1) which is almost double as compared to that of the Resovist, a commercially available MRI contrast agent. Thus the as-prepared magnetite nanoparticles may be used for hyperthermia and MRI applications due to their promising SAR and r2 values.