Structural properties of magnetic nanoparticles determine their heating behavior - an estimation of the in vivo heating potential

Magnetically induced heating of magnetic nanoparticles (MNP) in an alternating magnetic field (AMF) is a promising minimally invasive tool for localized tumor treatment by sensitizing or killing tumor cells with the help of thermal stress. Therefore, the selection of MNP exhibiting a sufficient heating capacity (specific absorption rate, SAR) to achieve satisfactory temperatures in vivo is necessary. Up to now, the SAR of MNP is mainly determined using ferrofluidic suspensions and may distinctly differ from the SAR in vivo due to immobilization of MNP in tissues and cells. The aim of our investigations was to study the correlation between the SAR and the degree of MNP immobilization in dependence of their physicochemical features.In this study, the included MNP exhibited varying physicochemical properties and were either made up of single cores or multicores. Whereas the single core MNP exhibited a core size of approximately 15 nm, the multicore MNP consisted of multiple smaller single cores (5 to 15 nm) with 65 to 175 nm diameter in total. Furthermore, different MNP coatings, including dimercaptosuccinic acid (DMSA), polyacrylic acid (PAA), polyethylenglycol (PEG), and starch, wereinvestigated. SAR values were determined after the suspension of MNP in water. MNP immobilization in tissues was simulated with 1% agarose gels and 10% polyvinyl alcohol (PVA) hydrogels.The highest SAR values were observed in ferrofluidic suspensions, whereas a strong reduction of the SAR after the immobilization of MNP with PVA was found. Generally, PVA embedment led to a higher immobilization of MNP compared to immobilization in agarose gels. The investigated single core MNP exhibited higher SAR values than the multicore MNP of the same core size within the used magnetic field parameters. Multicore MNP manufactured via different synthesis routes (fluidMAG-D, fluidMAG/12-D) showed different SAR although they exhibited comparable core and hydrodynamic sizes. Additionally, no correlation between ζ-potential and SAR values after immobilization was observed.Our data show that immobilization of MNP, independent of their physicochemical properties, can distinctly affect their SAR. Similar processes are supposed to take place in vivo, particularly when MNP are immobilized in cells and tissues. This aspect should be adequately considered when determining the SAR of MNP for magnetic hyperthermia.     

The heating effect of iron-cobalt magnetic nanofluids in an alternating magnetic field: application in magnetic hyperthermia treatment

In this research, FeCo alloy magnetic nanofluids were prepared by reducing iron(III) chloride hexahydrate and cobalt(II) sulfate heptahydrate with sodium borohydride in a water/CTAB/hexanol reverse micelle system for application in magnetic hyperthermia treatment. X-ray diffraction, electron microscopy, selected area electron diffraction, and energy-dispersive analysis indicate the formation of bcc-structured iron-cobalt alloy. Magnetic property assessment of nanoparticles reveals that some samples are single-domain superparamagnetic, while others are single- or multi-domain ferromagnetic. The stability of the magnetic fluids was achieved by using a CTAB/1-butanol surfactant bilayer. Results of Gouy magnetic susceptibility balance experiments indicate good stability of FeCo nanoparticles even after dilution. The inductive properties of corresponding magnetic fluids including temperature rise and specific absorption rate were determined. Results show that with increasing of the nanoparticle size in the single-domain size regime, the generated heat increases, indicating the significant effect of the hysteresis loss. Finally, the central parameter controlling the specific absorption rate of nanoparticles was introduced, the experimental results were compared with those of the Stoner-Wohlfarth model and linear response theory, and the best sample for magnetic hyperthermia treatment was specified.     

Morphological effect of oscillating magnetic nanoparticles in killing tumor cells

Forced oscillation of spherical and rod-shaped iron oxide magnetic nanoparticles (MNPs) via low-power and low-frequency alternating magnetic field (AMF) was firstly used to kill cancer cells in vitro. After being loaded by human cervical cancer cells line (HeLa) and then exposed to a 35-kHz AMF, MNPs mechanically damaged cell membranes and cytoplasm, decreasing the cell viability. It was found that the concentration and morphology of the MNPs significantly influenced the cell-killing efficiency of oscillating MNPs. In this preliminary study, when HeLa cells were pre-incubated with 100 μg/mL rod-shaped MNPs (rMNP, length of 200 ± 50 nm and diameter of 50 to 120 nm) for 20 h, MTT assay proved that the cell viability decreased by 30.9% after being exposed to AMF for 2 h, while the cell viability decreased by 11.7% if spherical MNPs (sMNP, diameter of 200 ± 50 nm) were used for investigation. Furthermore, the morphological effect of MNPs on cell viability was confirmed by trypan blue assay: 39.5% rMNP-loaded cells and 15.1% sMNP-loaded cells were stained after being exposed to AMF for 2 h. It was also interesting to find that killing tumor cells at either higher (500 μg/mL) or lower (20 μg/mL) concentration of MNPs was less efficient than that achieved at 100 μg/mL concentration. In conclusion, the relatively asymmetric morphological rod-shaped MNPs can kill cancer cells more effectively than spherical MNPs when being exposed to AMF by virtue of their mechanical oscillations.     

反相微乳液法制备纳米颗粒研究进展

综述了反相微乳液的形成机理、配制方法和目前利用反相微乳液技术制备纳米颗粒方面的研究进展，并对微乳液的配制及制备过程中影响纳米颗粒的主要因素进行了具体的讨论，还对微乳液技术的发展前景作了具体的讨论和分析。     

Immobilization on magnetic nanoparticles of the recombinant trehalose synthase from Deinococcus geothermalis

In our study the gene encoding trehalose synthase from Deinococcus geothermalis was cloned and overexpressed in Escherichia coli Rosetta (DE3)pLysS. Wild-type trehalose synthase has been purified from host protein after cell disruption and precipitation at 20% ammonium sulphate saturation. Recombinant trehalose synthase was immobilized onto glutaraldehyde activated silanized magnetic ferrous-ferric oxide by using covalent binding method. The morphology and surface of the obtained particles were characterized using SEM. These images show that all samples have a particle size below 30 nm. The obtained immobilized preparation has specific activity of 0.134 U/g support when measured at 40 °C using maltose as substrate. Immobilization process was almost fully completed after 30 min of the reaction at 30 °C. The highest immobilization yield of the enzyme was achieved at glutaraldehyde concentration of 10 mM. No significant differences in optimal pH and temperature were observed upon immobilization. The immobilized trehalose synthase exhibited mass transfer limitation, which is reflected by higher K_M and activation energy values. In addition, immobilized trehalose synthase was easily separated from the reaction medium by an external magnetic field and retained 82% of its initial activity after successive twelve repeated batches reaction.     

Chemical synthesis of FePt nanoparticles with high alternate current magnetic susceptibility for biomedical applications

The present paper describes ordered alloy FePt nanoparticles with high magnetic susceptibility to alternate current (ac) fields at around room temperature for biomedical applications such as magnetic sensing devices for diagnostics and magnetic hyperthermia for cancer therapy. Since ac magnetic susceptibility takes the maximum value at a temperature near the blocking temperature of magnetic nanoparticles, the blocking temperature of the FePt nanoparticles is required to be adjusted at around room temperature to improve biomedical performances. Ordered alloy FePt has much higher magnetic anisotropy than iron oxides, and it can be the best candidate in the case of their particle size less than 10 nm. The ordered alloy FePt nanoparticles are synthesized by reduction of Fe and Pt organo-metallic compounds with tetraethylene glycol using poly(N-vinyl-2-pyrrolidone) (PVP) as a protective agent. PVP is a water-soluble polymer, and is proper to obtain dispersion into water. Influences of reaction temperature on crystallite size (particle size) and blocking temperature and the relationship between the blocking temperature and the value of ac magnetic susceptibility at around room temperature are investigated. Furthermore, PVP concentration at the synthesis to obtain well dispersed nanoparticle-suspension is examined.     

Synthesis,structural, magnetic and NO2 gas sensing property of CuO nanoparticles

Cupric oxide (CuO) nanoparticles are synthesized by the oxidation of Cu/Cu₂O, which is obtained by the chemical reduction of Cu²⁺ ions with ascorbic acid. XRD pattern confirmed the formation of CuO, and FE-SEM image shows the clusters consisting of 25–30 nm sized particles. The band gap energy (3.7 eV) from optical absorption spectra is blue shifted to that of bulk values. The Néel temperature, T_N ≈ 230 K for paramagnetic to antiferromagnetic transition was clearly seen. The magnetic hysteresis loops at 5 K showed weak ferromagnetic behavior. Based on the dc electrical conductivity (300–500 K), the apparent activation energy was 0.36 eV. The NO₂ gas sensing property of CuO was reasonably good in the temperature range of 200–300 °C, and the sensitivity increased with an increase in gas concentration but the effect of temperature is marginal.     

纳米银粒子制备及应用研究进展

综述了制备纳米银粒子的方法,主要包括液相化学还原法,电化学还原法、光化学还原法和分子自组装等,分析比较了这些方法的基本原理、制备过程及优缺点,阐述了纳米银粒子在化学反应,光学领域及抗菌等领域的应用.     

Size dependence of the magnetic properties of Ni nanoparticles prepared by thermal decomposition method

By means of thermal decomposition, we prepared single-phase spherical Ni nanoparticles (23 to 114 nm in diameter) that are face-centered cubic in structure. The magnetic properties of the Ni nanoparticles were experimentally as well as theoretically investigated as a function of particle size. By means of thermogravimetric/differential thermal analysis, the Curie temperature T_C of the 23-, 45-, 80-, and 114-nm Ni particles was found to be 335°C, 346°C, 351°C, and 354°C, respectively. Based on the size-and-shape dependence model of cohesive energy, a theoretical model is proposed to explain the size dependence of T_C. The measurement of magnetic hysteresis loop reveals that the saturation magnetization M_S and remanent magnetization increase and the coercivity decreases monotonously with increasing particle size, indicating a distinct size effect. By adopting a simplified theoretical model, we obtained M_S values that are in good agreement with the experimental ones. Furthermore, with increase of surface-to-volume ratio of Ni nanoparticles due to decrease of particle size, there is increase of the percentage of magnetically inactive layer.     

The cytotoxicity evaluation of magnetic iron oxide nanoparticles on human aortic endothelial cells

One major obstacle for successful application of nanoparticles in medicine is its potential nanotoxicity on the environment and human health. In this study, we evaluated the cytotoxicity effect of dimercaptosuccinic acid-coated iron oxide (DMSA-Fe₂O₃) using cultured human aortic endothelial cells (HAECs). Our results showed that DMSA-Fe₂O₃ in the culture medium could be absorbed into HAECs, and dispersed in the cytoplasm. The cytotoxicity effect of DMSA-Fe₂O₃ on HAECs was dose-dependent, and the concentrations no more than 0.02 mg/ml had little toxic effect which were revealed by tetrazolium dye assay. Meanwhile, the cell injury biomarker, lactate dehydrogenase, was not significantly higher than that from control cells (without DMSA-Fe₂O₃). However, the endocrine function for endothelin-1 and prostacyclin I-2, as well as the urea transporter function, was altered even without obvious evidence of cell injury in this context. We also showed by real-time PCR analysis that DMSA-Fe₂O₃ exposure resulted in differential effects on the expressions of pro- and anti-apoptosis genes of HAECs. Meanwhile, it was noted that DMSA-Fe₂O₃ exposure could activate the expression of genes related to oxidative stress and adhesion molecules, which suggested that inflammatory response might be evoked. Moreover, we demonstrated by in vitro endothelial tube formation that even a small amount of DMSA-Fe₂O₃ (0.01 and 0.02 mg/ml) could inhibit angiogenesis by the HAECs. Altogether, these results indicate that DMSA-Fe₂O₃ have some cytotoxicity that may cause side effects on normal endothelial cells.     

Size-regulated group separation of CoFe2O4 nanoparticles using centrifuge and their magnetic resonance contrast properties

Magnetic nanoparticle (MNP)-based magnetic resonance imaging (MRI) contrast agents (CAs) have been the subject of extensive research over recent decades. The particle size of MNPs varies widely and is known to influence their physicochemical and pharmacokinetic properties. There are two commonly used methods for synthesizing MNPs, organometallic and aqueous solution coprecipitation. The former has the advantage of being able to control the particle size more effectively; however, the resulting particles require a hydrophilic coating in order to be rendered water soluble. The MNPs produced using the latter method are intrinsically water soluble, but they have a relatively wide particle size distribution. Size-controlled water-soluble MNPs have great potential as MRI CAs and in cell sorting and labeling applications. In the present study, we synthesized CoFe₂O₄ MNPs using an aqueous solution coprecipitation method. The MNPs were subsequently separated into four groups depending on size, by the use of centrifugation at different speeds. The crystal shapes and size distributions of the particles in the four groups were measured and confirmed by transmission electron microscopy and dynamic light scattering. Using X-ray diffraction analysis, the MNPs were found to have an inverse spinel structure. Four MNP groups with well-selected semi-Gaussian-like diameter distributions were obtained, with measured T₂ relaxivities (r₂) at 4.7 T and room temperature in the range of 60 to 300 mM⁻¹s⁻¹, depending on the particle size. This size regulation method has great promise for applications that require homogeneous-sized MNPs made by an aqueous solution coprecipitation method. Any group of the CoFe₂O₄ MNPs could be used as initial base cores of MRI T₂ CAs, with almost unique T₂ relaxivity owing to size regulation. The methodology reported here opens up many possibilities for biosensing applications and disease diagnosis.

PACS

75.75.Fk, 78.67.Bf, 61.46.Df     

A method to obtain the thermal parameters and the photothermal transduction efficiency in an optical hyperthermia device based on laser irradiation of gold nanoparticles

Optical hyperthermia systems based on the laser irradiation of gold nanorods seem to be a promising tool in the development of therapies against cancer. After a proof of concept in which the authors demonstrated the efficiency of this kind of systems, a modeling process based on an equivalent thermal-electric circuit has been carried out to determine the thermal parameters of the system and an energy balance obtained from the time-dependent heating and cooling temperature curves of the irradiated samples in order to obtain the photothermal transduction efficiency. By knowing this parameter, it is possible to increase the effectiveness of the treatments, thanks to the possibility of predicting the response of the device depending on the working configuration. As an example, the thermal behavior of two different kinds of nanoparticles is compared. The results show that, under identical conditions, the use of PEGylated gold nanorods allows for a more efficient heating compared with bare nanorods, and therefore, it results in a more effective therapy.     

Photocatalytic,magnetic, and electrochemical properties of La doped BiFeO3 nanoparticles

We successfully prepared La_1?xBi_xFeO₃ (L_xB_1?xFO, x?=?0.01–0.1) nanoparticles using a sol-gel technique, and studied their photocatalytic, magnetic, and electrochemical properties. Structural refinement studies of the prepared nanoparticles revealed a gradual structural transition from rhombohedral to orthorhombic. The average grain size was observed to decrease with increasing the concentration of La. The photocatalytic degradation of Rhodamine B (RhB) in the presence of the prepared nanoparticles was studied under visible light irradiation. The L_0.06B_0.94FO nanoparticles showed higher degradation efficiency compared to pure BiFeO₃ (BFO) nanoparticles. Magnetic studies showed that La doping improved the magnetization of BFO due to the reduction in grain size and destruction of cycloid coupling of spins. Higher specific capacitance values were obtained for La doped BFO (LBFO) nanoparticles compared to BFO nanoparticles. A maximum specific capacitance of 219?F?g^?1 was obtained at a current density of 1?A?g^?1 for LBFO nanoparticles.     

结构型磁性高分子的研究进展

磁性高分子分为复合型和结构型。针对结构型磁性高分子分子设计、合成及其性能研究进展进行了综述,展望了结构型磁性高分子的研究和应用前景。     

Preparation and magnetic behavior of carbon-encapsulated cobalt and nickel nanoparticles from starch

Carbon-encapsulated cobalt and nickel nanoparticles with core/shell structure have been successfully synthesized with maize-derived starch as carbon source and metal nitrate as metal precursors in flowing hydrogen. The as-prepared M@Cs materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction technique (XRD) and vibrating sample magnetometer (VSM). The effects of the metal precursors on the structure and the size of the M@Cs materials were investigated, and the magnetic properties of the M@Cs materials were measured. The results show that the structure and the size of the M@Cs materials are different in terms of the different metal precursors. The Co@Cs materials are made of the fcc-Co core and the graphitic carbon shell, of which the core diameter is in a range of 20–35 nm, while the Ni@Cs materials are composed of fcc-Ni core and the amorphous carbon shell, of which the core diameter ranges from 30 to 50 nm. The hysteresis loops of the as-made M@Cs materials show that some of the nanoparticles are in a superparamagnetic state at room temperature. A mechanism is proposed to explain the growth process of the M@Cs materials. It is believed that the starch with the helical structure is responsible for the formation of the M@Cs materials featuring the core/shell structure.     

Synthesis and functionalization of magnetic nanoparticles with covalently bound electroactive compound doxorubicin

We report here on covalent functionalization of magnetic nanoparticle colloidal suspension (ferrofluid) with doxorubicin. Since doxorubicin (adriamycin) is a potent anti-cancer drug, such particles can be guided with external magnetic field to a target tissue, a carrier process that may overcome the non-specificity and efficiency of adriamycin as a drug. The nanoferrite functionalization was effected by means of acid chloride chemistry leading to the formation of covalent bond between the hydroxyl groups at the nanoparticle surface and acid chloride molecules. This procedure can be easily tailored to provide the nanoferrites with various functionalities capable of further modifications with, e.g., drug molecules. Thus, we used such modified nanoferrites to covalently attach molecules of anti-tumor drug—doxorubicin. The attachment was verified by means of FTIR and cyclic voltammetry. Mean size of nanoferrites was evaluated by powder X-ray diffraction (PXRD) technique and high-resolution field emission scanning electron microscope (HR-FESEM). The amount of doxorubicin attached to nanoparticles was assessed by means of quartz crystal microbalance combined with cyclic voltammetry.