Preparation and characterization of thermosensitive polymers grafted onto silica-coated iron oxide nanoparticles

In this study, multifunctional nanoparticles containing thermosensitive polymers grafted onto the surfaces of 6-nm monodisperse Fe(3)O(4) magnetic nanoparticles coated by silica were synthesized using reverse microemulsions and free radical polymerization. The magnetic properties of SiO(2)/Fe(3)O(4) nanoparticles show superparamagnetic behavior. Thermosensitive PNIPAM (poly(N-isopropylacrylamide)) was then grafted onto the surfaces of SiO(2)/Fe(3)O(4) nanoparticles, generating thermosensitive and magnetic properties of nanocomposites. The sizes of fabricated nanoparticles with core-shell structure are controlled at about 30 nm and each nanoparticle contains only one monodisperse Fe(3)O(4) core. For thermosensitivity analysis, the phase transition temperatures of multifunctional nanoparticles measured using DSC was at around 34-36 degrees C. The magnetic characteristics of these multifunctional nanoparticles were also superparamagnetic.     

壳核型磁性纳米纤维素微球的超声制备及表征

A kind of cellulose magnetic nanoparticle with a core / shell structure has been prepared by ultrasonic irradiation. Cellulose acts as the shell while Fe3O4 magnetic nanoparticles take the role as the core. Magnetic force microscopy（MFM）with atomic force microscopy（AFM）measurement showed that the size of the magnetic nanoparticles is about 30-50 nm in diameter,while the Fe3O4 core is about 20-30 nm. FT-IR,XRD and MFM was used to provide the chemical and magnetic information of the nanoparticles. The MFM image showed that the nanoparticles separate very well with each other,indicating the cellulose shell produces a good prevention from the aggregation of the Fe3O4 particles. MFM studies also showed two magnetic nanoparticles can form particle-pairs,indicating a weak magneto-dipole interaction between magnetic nanoparticles. It is also found that the average sizes of magnetic nanoparticles have relation to the power of ultrasonic irradiation,and the possible mechanism is discussed.     

磁性聚苯胺纳米微球的合成与表征

报道了具有核壳结构的Fe3O4-聚苯胺磁性纳米微球的合成方法和表征结果.微球同时具有导电性和磁性能.在优化的实验条件下,可得到饱和磁化强度Ms为55.4 emu/g,矫顽力Hc为62 Oe的磁性微球.微球的导电性随着微球中Fe含量的增加而下降.微球的磁性能则随着Fe含量的增加而增大.Fe3O4磁流体的粒径和磁性聚苯胺微球的粒径均在纳米量级.纳米Fe3O4粒子能够提高复合物的热性能.实验表明,磁流体和聚苯胺之间可能存在着一定的相互作用,但这种相互作用较为复杂,难于研究     

Fe_3O_4/CdTe/聚氨酯纳米复合物的制备及其性能研究

由共沉淀法和Stober法制备了伯胺基功能化SiO2稳定的Fe3O4磁性纳米粒子Fe3O4@SiO2-NH2;Fe3O4@SiO2-NH2与二异氰酸酯及咪唑阳离子二醇、聚乙二醇的反应使其表面形成阳离子型聚氨酯稳定层;通过阳离子型聚氨酯与CdTe量子点表面修饰的巯基乙酸间的电荷相互作用,制备得到了Fe3O4/CdTe/聚氨酯纳米复合物.用X射线衍射(XRD)、红外吸收光谱(FTIR)、热重分析(TGA)、透射电子显微镜(TEM)、磁强计(VSM)、紫外吸收光谱(UV)、荧光发射光谱(PL)表征了该纳米复合物的结构与性能.结果表明,CdTe量子点均匀地分散在Fe3O4@SiO2磁性纳米粒子周围,所得纳米复合物在溶剂中分散均匀,不团聚,且具有超顺磁性,并保持了CdTe量子点的荧光性能.     

Magnetite nanoparticles with tunable gold or silver shell

Fe3O4 nanoparticles with size approximately 13 nm have been prepared successfully in aqueous micellar medium at approximately 80 degrees C. To make Fe3O4 nanoparticles resistant to surface poisoning a new route is developed for coating Fe3O4 nanoparticles with noble metals such as gold or silver as shell. The shell thickness of the core-shell particles becomes tunable through the adjustment of the ratio of the constituents. Thus, the route yields well-defined core-shell structures of size from 18 to 30 nm with varying proportion of Fe3O4 to the noble metal precursor salts. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FTIR, differential scanning calorimetry (DSC), Raman and temperature-dependent magnetic studies.     

Preparation of surface plasmon resonance biosensor based on magnetic core/shell Fe3O4/SiO2 and Fe3O4/Ag/SiO2 nanoparticles

In this paper, surface plasmon resonance biosensors based on magnetic core/shell Fe(3)O(4)/SiO(2) and Fe(3)O(4)/Ag/SiO(2) nanoparticles were developed for immunoassay. With Fe(3)O(4) and Fe(3)O(4)/Ag nanoparticles being used as seeding materials, Fe(3)O(4)/SiO(2) and Fe(3)O(4)/Ag/SiO(2) nanoparticles were formed by hydrolysis of tetraethyl orthosilicate. The aldehyde group functionalized magnetic nanoparticles provide organic functionality for bioconjugation. The products were characterized by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), FTIR and UV-vis absorption spectrometry. The magnetic nanoparticles possess the unique superparamagnetism property, exceptional optical properties and good compatibilities, and could be used as immobilization matrix for goat anti-rabbit IgG. The magnetic nanoparticles can be easily immobilized on the surface of SPR biosensor chip by a magnetic pillar. The effects of Fe(3)O(4)/SiO(2) and Fe(3)O(4)/Ag/SiO(2) nanoparticles on the sensitivity of SPR biosensors were also investigated. As a result, the SPR biosensors based on Fe(3)O(4)/SiO(2) nanoparticles and Fe(3)O(4)/Ag/SiO(2) nanoparticles exhibit a response for rabbit IgG in the concentration range of 1.25-20.00 μg ml(-1) and 0.30-20.00 μg ml(-1), respectively.     

Fe3O4-LiMo3Se3 nanoparticle clusters as superparamagnetic nanocompasses

A scaleable chemical approach to functional nanoscale analogues of the magnetic compasses in magnetotactic bacteria is described. LiMo(3)Se(3)-Fe(3)O(4) nanowire-nanoparticle composites were synthesized by a reaction of 3-iodopropionic acid treated LiMo(3)Se(3) nanowire bundles with oleic acid-stabilized Fe(3)O(4) nanoparticles of 2.8, 5.3, and 12.5 nm size in tetrahydrofuran. Transmission electron micrographs show that the composite consists of Fe(3)O(4) nanoparticles attached to the surfaces of the 4-6 nm thick nanowire bundles. UV/vis spectra reveal absorptions from the nanowire (506 nm) and magnetite components (280-450 nm), and IR spectra show characteristic bands for the propionic acid linkers and for the residual oleic acid ligands on the magnetite particles. In the presence of excess oleic acid, the nanocomposites undergo rapid disassembly, suggesting that Fe(3)O(4) nanoparticles are bonded to nanowires via carboxylate groups from the linkers. Ultrasonication of a dispersion of the composite in THF produces individual LiMo(3)Se(3)-Fe(3)O(4) clusters, which are 340 +/- 107 nm long and 20 +/- 5 nm thick, depending on the sonication time and Fe(3)O(4) nanoparticle size. Field cooled and zero-field cooled magnetization measurements reveal that the blocking temperature (T(B) = 100 K) of the clusters with 5.3 nm Fe(3)O(4) is increased as compared to the free nanoparticles (T(B) = 30 K). Directional dipolar interactions in the clusters lead to magnetic anisotropy, which makes it possible to align the clusters in a magnetic field (900 Oe).     

Preparation and properties of magnetic alumina microspheres with a γ-Fe_2O_3/SiO_2 core and Al_2O_3 shell

Magnetic alumina composite microspheres with γ-Fe 2 O 3 core/Al 2 O 3 shell structure were prepared by the oil column method. A dense silica layer was deposited on the surface of γ-Fe 2 O 3 particles (denoted as γ-Fe 2 O 3 /SiO 2 ) with a desired thickness to protect the iron oxide core against acidic or high temperature conditions. γ-Fe 2 O 3 /SiO 2 /Al 2 O 3 particles with about 85 wt% Al 2 O 3 were obtained and showed to be suitable for practical applications as a magnetic catalyst or catalyst support due to their magnetic properties and pore structure. The products were characterized with scanning electron microscope (SEM) and transmission electron microscope (TEM), nitrogen adsorption-desorption, and vibrating sample magnetometer (VSM). The specific surface area and pore volume of the γ-Fe 2 O 3 /SiO 2 /Al 2 O 3 composite microspheres calcined at 500 ? C were 200 m 2 /g and 0.77 cm 3 /g, respectively.     

Preparation of silica-magnetite nanoparticle mixed hemimicelle sorbents for extraction of several typical phenolic compounds from environmental water samples

A novel type of superparamagnetic silica-coated (Fe3O4/SiO2 core/shell) magnetite nanoparticle modified by surfactants has been successfully synthesized and was applied as an effective sorbent material for the pre-concentration of several typical phenolic compounds (bisphenol A (BPA), 4-tert-octylphenol (4-OP) and 4-n-nonylphenol (4-NP)) from environmental water samples. Compared with pure magnetic particles, a thin and dense silica layer would protect the iron oxide core from leaching out in acidic conditions. In order to enhance their adsorptive tendency towards organic compounds, cetylpyridinium chloride (CPC) or cetyltrimethylammonium bromide (CTAB) were added, which adsorbed on the surface of the Fe3O4/SiO2 nanoparticles (Fe3O4/SiO2 NPs) and formed mixed hemimicelles. Main factors affecting the adsolubilization of analytes were optimized and comparative study on the use of CPC and CTAB-coated Fe3O4/SiO2 NPs mixed hemimicelles-based SPE was also carried out. CPC-coated Fe3O4/SiO2 NPs system was selected due to lower elution volume required and more effective adsorption of the target compounds. Under selected conditions, concentration factor of 1600 was achieved by using this method to extract 800 mL of different environmental water samples. The detection limits obtained for BPA, 4-OP and 4-NP with HPLC-FLD were 7, 14, and 20 ng/L, respectively.     

Fe3O4/Polypyrrole/Au nanocomposites with core/shell/shell structure: synthesis, characterization, and their electrochemical properties

Uniform Fe3O4 nanospheres with a diameter of 100 nm were rapidly prepared using a microwave solvothermal method. Then Fe304/polypyrrole (PPy) composite nanospheres with well-defined core/shell structures were obtained through chemical oxidative polymerization of pyrrole in the presence of Fe3O4; the average thickness of the coating shell was about 25 nm. Furthermore, by means of electrostatic interactions, plentiful gold nanoparticles with a diameter of 15 nm were assembled on the surface of Fe3O4/PPy to get Fe3O4/PPy/Au core/shell/shell structure. The morphology, structure, and composition of the products were characterized by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), X-ray powder diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The resultant nanocomposites not only have the magnetism of Fe3O4 nanoparticles that make the nanocomposites easily controlled by an external magnetic field but also have the good conductivity and excellent electrochemical and catalytic properties of PPy and Au nanoparticles. Furthermore, the nanocomposites showed excellent electrocatalytic activities to biospecies such as ascorbic acid (AA).     

A new ion-exchange adsorbent with paramagnetic properties for the separation of genomic DNA

A new ion-exchange adsorbent (IEA) derived from Fe(3)O(4)/SiO(2)-GPTMS-DEAE with paramagnetic properties was prepared. Fe(3)O(4) nanoparticles were firstly prepared in water-in-oil microemulsion. The magnetic Fe(3)O(4) particles were modified in situ by hydrolysis and condensation reactions with tetraethoxysilane (TEOS) to form the core-shell Fe(3)O(4)/SiO(2). The modified particles were further treated by 3-glycidoxypropyltrimethoxysilane (GPTMS) to form Fe(3)O(4)/SiO(2)-GPTMS nanoparticles. Fe(3)O(4)/SiO(2)-GPTMS-DEAE nanoparticles (IEA) were finally obtained through the condensation reaction between the Cl of diethylaminoethyl chloride-HCl (DEAE) and the epoxy groups of GPTMS in the Fe(3)O(4)/SiO(2)-GPTMS. The obtained IEA has features of paramagnetic and ion exchange properties because of the Fe(3)O(4) nanoparticles and protonated organic amine in the sample. The intermediates and final product obtained in the synthesis process were characterized. The separation result of genomic DNA from blood indicated that Fe(3)O(4)/SiO(2)-GPTMS-DEAE nanoparticles have outstanding advantages in operation, selectivity, and capacity.     

Monodispersed core-shell Fe3O4@Au nanoparticles

The ability to synthesize and assemble monodispersed core-shell nanoparticles is important for exploring the unique properties of nanoscale core, shell, or their combinations in technological applications. This paper describes findings of an investigation of the synthesis and assembly of core (Fe(3)O(4))-shell (Au) nanoparticles with high monodispersity. Fe(3)O(4) nanoparticles of selected sizes were used as seeding materials for the reduction of gold precursors to produce gold-coated Fe(3)O(4) nanoparticles (Fe(3)O(4)@Au). Experimental data from both physical and chemical determinations of the changes in particle size, surface plasmon resonance optical band, core-shell composition, surface reactivity, and magnetic properties have confirmed the formation of the core-shell nanostructure. The interfacial reactivity of a combination of ligand-exchanging and interparticle cross-linking was exploited for molecularly mediated thin film assembly of the core-shell nanoparticles. The SQUID data reveal a decrease in magnetization and blocking temperature and an increase in coercivity for Fe(3)O(4)@Au, reflecting the decreased coupling of the magnetic moments as a result of the increased interparticle spacing by both gold and capping shells. Implications of the findings to the design of interfacial reactivities via core-shell nanocomposites for magnetic, catalytic, and biological applications are also briefly discussed.     

New preparation method of gold nanoparticles on SiO2

It is shown that adsorption of the [Au(en)(2)](3+) cationic complex can be successfully employed for the deposition of gold nanoparticles (1.5 to 3 nm) onto SiO(2) with high metal loading, good dispersion, and small Au particle size. When the solution pH increases (from 3.8 to 10.5), the Au loading in the Au/SiO(2) samples increases proportionally (from 0.2 to 5.5 wt %), and the average gold particle size also increases (from 1.5 to 2.4 nm). These effects are explained by the increase in the amount of negatively charged sites present on the SiO(2) surface, namely, when the solution pH increases, a higher number of [Au(en)(2)](3+) species can be adsorbed. Extending the adsorption time from 2 to 16 h gives rise to an increase in the gold loading from 3.3 to 4.0 wt % and in the average particle size from 1.8 to 2.9 nm. Different morphologies of gold nanoparticles are present as a function of the particle size. Particles with a size of 3-5 nm show defective structure, some of them having a multiple twinning particle (MTP) structure. At the same time, nanoparticles with an average size of ca. 2 nm exhibit defect-free structure with well-distinguishable {111} family planes. TEM and HAADF observations revealed that Au particles do not agglomerate on the SiO(2) support: gold is present on the surface of SiO(2) only as small particles. Density functional theory calculations were employed to study the mechanisms of [Au(en)(2)](3+) adsorption, where neutral and negatively charged silica surfaces were simulated by neutral cluster Si(4)O(10)H(4) and negatively charged cluster Si(4)O(10)H(3), respectively. The calculation results are totally consistent with the suggestion that the deposition of gold takes place according to a cationic adsorption mechanism.     

Adsorption of nanoparticles at the solid-liquid interface

The adsorption of differently charged nanoparticles at liquid-solid interfaces was investigated by in situ X-ray reflectivity measurements. The layer formation of positively charged maghemite (γ-Fe(2)O(3)) nanoparticles at the aqueous solution-SiO(2) interface was observed while negatively charged gold nanoparticles show no adsorption at this interface. Thus, the electrostatic interaction between the particles and the charged surface was determined as the driving force for the adsorption process. The data analysis shows that a logarithmic particle size distribution describes the density profile of the thin adsorbed maghemite layer. The size distribution in the nanoparticle solution determined by small angle X-ray scattering shows an average particle size which is similar to that found for the adsorbed film. The formed magehemite film exhibits a rather high stability.     

Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: comparison of experiment and theory

Understanding plasmonic enhancement of nanoscale magnetic materials is important to evaluate their potential for application. In this study, the Faraday rotation (FR) enhancement of gold coated Fe(2)O(3) nanoparticles (NP) is investigated experimentally and theoretically. The experiment shows that the Faraday rotation of a Fe(2)O(3) NP solution changes from approximately 3 rad/Tm to 10 rad/Tm as 5 nm gold shell is coated on a 9.7 nm Fe(2)O(3) core at 632 nm. The results also show how the volume fraction normalized Faraday rotation varies with the gold shell thickness. From the comparison of experiment and calculated Faraday rotation based on the Maxwell-Garnett theory, it is concluded that the enhancement and shell dependence of Faraday rotation of Fe(2)O(3) NPs is a result of the shifting plasmon resonance of the composite NP. In addition, the clustering of the NPs induces a different phase lag on the Faraday signal, which suggests that the collective response of the magnetic NP aggregates needs to be considered even in solution. From the Faraday phase lag, the estimated time of the full alignment of the magnetic spins of bare (cluster size 160 nm) and gold coated NPs (cluster size 90 nm) are found to be 0.65 and 0.17 μs. The calculation includes a simple theoretical approach based on the Bruggeman theory to account for the aggregation and its effect on the Faraday rotation. The Bruggeman model provides a qualitatively better agreement with the experimentally observed Faraday rotation and points out the importance of making a connection between component properties and the average "effective" optical behavior of the Faraday medium containing magnetic nanoparticles.     

磁性Fe_3O_4-聚吡咯纳米微球的合成与表征

报道了具有核壳结构的Fe3O4 聚吡咯磁性纳米微球的合成方法和表征结果 .微球同时具有导电性和磁性能 .在优化的实验条件下 ,可得到饱和磁化强度为 2 3 4emu g ,矫顽力为 45 2Oe的磁性微球 .微球的导电性随着微球中Fe3O4含量的增加而下降 .微球的磁性能则随着Fe3O4含量的增加而增大 .Fe3O4磁流体的粒径和磁性聚吡咯微球的粒径均在纳米量级 .纳米Fe3O4粒子能够提高复合物的热性能 .实验表明 ,磁流体和聚吡咯之间存在着一定的相互作用 ,正是这种相互作用使磁性聚吡咯纳米微球的热稳定性提高 .     

Synthesis, characterization, and 3D-FDTD simulation of Ag@SiO2 nanoparticles for shell-isolated nanoparticle-enhanced Raman spectroscopy

Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.     

Alkanethiol-induced structural rearrangements in silica-gold core-shell-type nanoparticle clusters: an opportunity for chemical sensor engineering

Electrostatically bonded SiO2.Au nanoparticle clusters form by reaction of 3-aminopropylsilane-modified SiO2 spheres (470 nm) with citrate-coated gold nanoparticles (9.7 nm) in water. Reaction of the clusters with 0.01 M KBr or HCl solution induces desorption of the gold nanoparticles within minutes. Reaction of the clusters with alkanethiols CnH2n+1SH (n = 2-18) at 80 degrees C causes the gold nanoparticles to form stringlike gold nanoparticle structures for thiols with short alkane groups (n = 2, 3, 4) and hexagonally packed arrays of gold nanoparticles for thiols with long alkane groups (n = 5-18) on the silica surfaces. The structural changes indicate that the bonding between Au and SiO2 nanoparticles has changed from electrostatic to van der Waals. Elemental analyses show that the reaction with hexanethiol does not affect the Au/Si/O composition of the SiO2.Au cluster, and Raman spectra on the hexanethiol-reacted cluster indicate the formation of a thiol SAM on the gold nanoparticles. The thiol-reacted SiO2.Au clusters display characteristic shifts of the absorption maxima in the visible spectra, and there is an inverse relation between these shifts and the lengths of the alkyl groups in the thiols. This relationship can be understood in terms of the free electron model for metals. The use of SiO2.Au nanoparticle clusters as coulometric sensors for the qualitative detection of thiols is discussed.     

Fabrication of magnetic core@shell Fe oxide@Au nanoparticles for interfacial bioactivity and bio-separation

The immobilization of proteins on gold-coated magnetic nanoparticles and the subsequent recognition of the targeted proteins provide an effective means for the separation of proteins via application of a magnetic filed. A key challenge is the ability to fabricate such nanoparticles with the desired core-shell nanostructure. In this article, we report findings of the fabrication and characterization of gold-coated iron oxide (Fe2O3 and Fe3O4) core@shell nanoparticles (Fe oxide@Au) toward novel functional biomaterials. A hetero-interparticle coalescence strategy has been demonstrated for fabricating Fe oxide@Au nanoparticles that exhibit controllable sizes ranging from 5 to 100 nm and high monodispersity. Composition and surface analyses have proven that the resulting nanoparticles consist of the Fe2O3 core and the Au shell. The magnetically active Fe oxide core and thiolate-active Au shell were shown to be viable for exploiting the Au surface protein-binding reactivity for bioassay and the Fe oxide core magnetism for magnetic bioseparation. These findings are entirely new and could form the basis for fabricating magnetic nanoparticles as biomaterials with tunable size, magnetism, and surface binding properties.     

肿瘤靶向的磁性荧光IR780-Fe3O4纳米颗粒用于循环肿瘤细胞的检测

循环肿瘤细胞(Circulating tumor cells,CTCs)的简单、快速分离和检测是目前临床研究中面临的一项挑战.本研究制备了具有肿瘤靶向识别作用的磁性荧光IR780-Fe3 O4纳米颗粒,并将其用于CTCs的分离和检测.通过电镜、荧光光谱仪和超导量子干涉仪对合成的IR780-Fe3 O4纳米颗粒进行表征;采用激光共聚焦显微镜和流式细胞仪对IR780-Fe3 O4纳米颗粒对肿瘤细胞和正常细胞的靶向效果进行了分析;利用激光共聚焦显微镜对IR780-Fe3 O4纳米颗粒在MCF-7细胞中的位置进行定位;并根据IR780-Fe3 O4纳米颗粒孵育后肿瘤细胞的荧光强度绘制标准曲线.研究结果表明,IR780-Fe3 O4能很好地靶向多种CTCs.细胞定位实验进一步表明,IR780-Fe3 O4主要靶向识别肿瘤细胞的线粒体.通过Fe3 O4磁性纳米颗粒偶联IR780建立的这种方法可很好地区分肿瘤细胞和正常细胞,并对模拟血液中的CTCs进行了分离和检测.