Gold-decorated magnetic nanoparticles design for hyperthermia applications and as a potential platform for their surface-functionalization.

The integration of noble metal and magnetic nanoparticles with controlled structures that can couple various specific effects to the different nanocomposite in multifunctional nanosystems have been found interesting in the field of medicine. In this work, we show synthesis route to prepare small Au nanoparticles of sizes = 3.9 ± 0.2 nm attached to Fe3O4 nanoparticle cores ( = 49.2 ± 3.5 nm) in aqueous medium for potential application as a nano-heater. Remarkably, the resulted Au decorated PEI-Fe3O4 (Au@PEI-Fe3O4) nanoparticles are able to retain bulk magnetic moment MS = 82-84 Am2/kgFe3O4, with the Verwey transition observed at TV = 98 K. In addition, the in vitro cytotoxicity analysis of the nanosystem microglial BV2 cells showed high viability (>97.5%) to concentrate up to 100 µg/mL in comparison to the control samples. In vitro heating experiments on microglial BV2 cells under an ac magnetic field (H0 = 23.87 kA/m; f = 571 kHz) yielded specific power absorption (SPA) values of SPA = 43 ± 3 and 49 ± 1 µW/cell for PEI-Fe3O4 and Au@PEI-Fe3O4 NPs, respectively. These similar intracellular SPA values imply that functionalization of the magnetic particles with Au did not change the heating efficiency, providing at the same time a more flexible platform for multifunctional functionalization.

Structural and magnetic properties of core-shell Au/Fe3O4 nanoparticles.

We present a systematic study of core-shell Au/Fe3O4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB = 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell.

The structure of graphite oxide: investigation of its surface chemical groups.

The structure of graphite oxide (GO) has been systematically studied using various tools such as SEM, TEM, XRD, Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), (13)C solid-state NMR, and O K-edge X-ray absorption near edge structure (XANES). The TEM data reveal that GO consists of amorphous and crystalline phases. The XPS data show that some carbon atoms have sp(3) orbitals and others have sp(2) orbitals. The ratio of sp(2) to sp(3) bonded carbon atoms decreases as sample preparation times increase. The (13)C solid-state NMR spectra of GO indicate the existence of -OH and -O- groups for which peaks appear at 60 and 70 ppm, respectively. FT-IR results corroborate these findings. The existence of ketone groups is also implied by FT-IR, which is verified by O K-edge XANES and (13)C solid-state NMR. We propose a new model for GO based on the results; -O-, -OH, and -C=O groups are on the surface.