Au-Fe3O4 Nanoparticles Research Articles

Synthesis of magnetic core–shell Fe3O4–Au nanoparticle for biomolecule immobilization and detection

The production of monodispersed magnetic nanoparticles with appropriate surface modification has attracted increasing attention in biomedical applications including drug delivery, separation, and purification of biomolecules from the matrices. In the present study, we report rapid and room temperature reaction synthesis of gold-coated iron nanoparticles in aqueous solution using the borohydride reduction of HAuCl4 under sonication for the first time. The resulting nanoparticles were characterized with transmission electron microscopy (TEM), electron spectroscopy for chemical analysis (ESCA), ultraviolet visible spectroscopy (UV–Vis), and X-ray diffraction (XRD). Surface charges and magnetic properties of the nanoparticles were also examined. The pattern of Fe3O4 nanoparticles is face centered cubic with an average diameter of 9.5 nm and the initial reduction of gold on the surface of Fe3O4 particles exhibits uniform Fe3O4–Au nanoparticles with an average diameter of 12.5 nm. The saturation magnetization values for the uncoated and gold-coated Fe3O4 nanoparticles were found to be 30 and 4.5 emu/g, respectively, at 300 K. The progression of binding events between boronic acid terminated ligand shell and fructose based on the covalent bonding interaction was measured by absorbance spectral changes. Immunomagnetic separation was also performed at different E. coli concentration to evaluate capturing efficiency of resulting nanoparticles. Immunomagnetic separation percentages were varied in a range of 52.1 and 21.9% depend on the initial bacteria counts.

Interparticle interactions in coupled Au–Fe3O4 nanoparticles

Complex ac susceptibility measurements are reported on composite Au–Fe3O4 nanoparticles of two different configurations—the so-called “dumbbell” and “flower” configurations. The frequency-dependent blocking temperature was fitted to two separate models in an attempt to understand the relaxation and the role of interactions present in the nanoparticle arrays. While the Néel–Arrhenius model failed to accurately describe the blocking behavior of both types of particles, the Vogel–Fulcher model was shown to fit the dumbbell particles indicating the importance of weak interparticle interactions in this system. The flower nanoparticles, however, failed to yield physical fit parameters for both models, indicating that the interactions present in these particles are not solely dipolar but likely associated with competing intraparticle interactions. Radio-frequency transverse susceptibility measurements also confirm these features.

Simple and Generalized Synthesis of Oxide−Metal Heterostructured Nanoparticles and their Applications in Multimodal Biomedical Probes

Heterostructured nanoparticles composed of metals and Fe3O4 or MnO were synthesized by thermal decomposition of mixtures of metal-oleate complexes (for the oxide component) and metal-oleylamine complexes (for the metal component). The products included flowerlike-shaped nanoparticles of Pt-Fe3O4 and Ni-Fe3O4 and snowmanlike-shaped nanoparticles of Ag-MnO and Au-MnO. Powder X-ray diffraction patterns showed that these nanoparticles were composed of face-centered cubic (fcc)-structured Fe3O4 or MnO and fcc-structured metals. The relaxivity values of the Au-MnO and Au-Fe3O4 nanoparticles were similar to those of the MnO and Fe3O4 nanoparticles, respectively. Au-Fe3O4 heterostructured nanoparticles conjugated with two kinds of 12-base oligonucleotide sequences were able to sense a complementary 24-mer sequence, causing nanoparticle aggregation. This hybridization-mediated aggregation was detected by the overall size increase indicated by dynamic light scattering data, the red shift of the surface plasmon band of the Au component, and the enhancement of the signal intensity of the Fe3O4 component in T2-weighted magnetic resonance imaging.

Au-Fe3O4 dumbbell nanoparticles as dual-functional probes.

Heavy lifting: Dumbbell-shaped Au–Fe3O4 nanoparticles are made biocompatible and suitable for attachment to A431 cells. The particles are magnetically and optically active and are useful for simultaneous magnetic and optical detection (see picture). The Au–Fe3O4 nanoparticles are promising as a new type of multifunctional probe for diagnostic and therapeutic applications. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z704392_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Self-assembly and magnetism in core-shell microspheres

We report on the fabrication and characterization of magnetic composite colloids with a defined shape, composition and multilayer shell thickness. They consist of a core of a polystyrene microsphere (640 nm diameter) coated with consecutive shells of Fe3O4 nanoparticles (12 nm diameter), polyelectrolytes and Au nanoparticles (15 nm). The homogeneity of the coating was confirmed by transmission electron microscopy. Composite core-shell microspheres were self-assembled into periodically ordered chains up to 2 mm in length by magnetophoretic deposition. The self-organization was visualized by optical and atomic force microscopy. Magnetic properties were determined by angular dependent ferromagnetic resonance (FMR) and superconducting quantum interference device magnetometry between 5 and 300 K. The FMR reveals long-range magnetic order at 300 K due to dipolar coupling and an easy axis in plane along the chains. We find a magnetic moment that is reduced in comparison with the magnetite bulk value.