M.H. Sousa

Biocompatible magnetic fluid precursors based on aspartic and glutamic acid modified maghemite nanostructures

Abstract Biocompatible magnetic fluid precursors based on chemically modified maghemite nanostructures (γ-Fe 2 O 3 ) are able to chemisorb aspartic and glutamic acids, as shown by conductometric measurements. The amino acids adsorb onto the maghemite surface following an adsorption isotherm. The modified nanoparticles formed a stable colloidal solution at a pH of 5–8. Raman and FTIR spectroscopy directly showed that the investigated amino acids adsorb on the maghemite surface in the form of their respective salts, glutamate and aspartate.

Magnetic hyperthermia investigation of cobalt ferrite nanoparticles: Comparison between experiment, linear response theory, and dynamic hysteresis simulations

Considerable effort has been made in recent years to optimize materials properties for magnetic hyperthermia applications. However, due to the complexity of the problem, several aspects pertaining to the combined influence of the different parameters involved still remain unclear. In this paper, we discuss in detail the role of the magnetic anisotropy on the specific absorption rate of cobalt-ferrite nanoparticles with diameters ranging from 3 to 14 nm. The structural characterization was carried out using x-ray diffraction and Rietveld analysis and all relevant magnetic parameters were extracted from vibrating sample magnetometry. Hyperthermia investigations were performed at 500 kHz with a sinusoidal magnetic field amplitude of up to 68 Oe. The specific absorption rate was investigated as a function of the coercive field, saturation magnetization, particle size, and magnetic anisotropy. The experimental results were also compared with theoretical predictions from the linear response theory and dynamic h...

Toxic effects of ionic magnetic fluids in mice

Abstract Toxicity of ionic and tartrate-based magnetic fluids administered intraperitoneally to mice was investigated through morphological and cytometric alterations and cytogenetic analysis. Both magnetic fluids cause cellular death, mutagenicity and severe inflammatory reactions, being very toxic and thus not biocompatible. Peritoneal cell and tissue studies may provide a useful strategy to investigate the in vivo biological effects of magnetic nanoparticles.

Field dependent transition to the non-linear regime in magnetic hyperthermia experiments: Comparison between maghemite, copper, zinc, nickel and cobalt ferrite nanoparticles of similar sizes

Further advances in magnetic hyperthermia might be limited by biological constraints, such as using sufficiently low frequencies and low field amplitudes to inhibit harmful eddy currents inside the patients body. These incite the need to optimize the heating efficiency of the nanoparticles, referred to as the specific absorption rate (SAR). Among the several properties currently under research, one of particular importance is the transition from the linear to the non-linear regime that takes place as the field amplitude is increased, an aspect where the magnetic anisotropy is expected to play a fundamental role. In this paper we investigate the heating properties of cobalt ferrite and maghemite nanoparticles under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe. The particles were characterized by TEM, XRD, FMR and VSM, from which most relevant morphological, structural and magnetic properties were inferred. Both materials have similar size distributions and satu...

Surface spin freezing of ferrite nanoparticles evidenced by magnetization measurements

Magnetization and in-field Mossbauer measurements were performed on copper ferrite nanoparticles with average sizes ranging from 3.5 to 10.4nm. Our results show that the nanoparticles are well-crystallized single domains with a magnetically disordered surface shell. A sharp increase in the saturation magnetization at low temperatures, in addition to the usual modified Bloch behavior, was observed for the smallest particles. This jump in magnetization curves seems to be related to the freezing of the surface spins below a temperature of about 45K.

Optical properties of nickel ferrite ferrofluids

We investigate magneto-optical properties of chemically synthesized ionic ferrofluids based on nickel ferrite nanoparticles. These new ferrofluids with potential biological applications become birefringent under low magnetic fields. Both a static and a dynamic probing are here presented.

Raman study of ionic water-based copper and zinc ferrite magnetic fluids

Raman spectroscopy is used to investigate the OH-bending and OH-stretching modes of chemisorbed OH-groups in copper-ferrite and zinc-ferrite water-based magnetic fluid samples. Room-temperature Raman spectra were taken from diluted magnetic fluid samples and compared with the spectrum taken from liquid water. The suppression of the symmetric OH-stretching Raman modes from the ionic magnetic fluid sample spectra is discussed in terms of the replacement of a hydrogen atom from the water molecule by the nanoparticle surface. Moreover, changes on the area ratio between hydrogen bonded and nonhydrogen bonded OH-Raman peaks in the ionic magnetic fluid samples, as compared to the OH-Raman peaks from liquid water, are discussed in terms of changes on the hydrogen bond strength.

Facile green synthesis of nanomagnets for modulating magnetohyperthermia: tailoring size, shape and phase

This study reports the successful production of both isometric and anisometric iron oxide-based nanoparticles using, respectively, ammonia and urea for co-precipitating Fe2+/Fe3+ from aqueous solution. Spherical nanoparticles (SNPs) with 10–20 nm in diameter are obtained using ammonia under reflux from 1 h to 9 h, with their relative magnetite/maghemite content decreasing from 10 to 0.05. However, using a lower and higher concentration of urea under reflux from 1 h to 12 h results in rod-like nanoparticles (RNPs) with length/width varying from 40/16 to 80/20 nm and hexagonal nanoparticles (HNPs) with diagonal varying from 150 to 100 nm, respectively. For RNPs (HNPs) the relative magnetite/goethite content increases with refluxing time from 0.25 to 2 (1.25 to 3.75). Hysteresis cycles (300 K) show unblocked SNPs and blocked RNPs and HNPs with coercivity (remanence) increasing with refluxing time from 55 to 80 Oe (1 to 5 emu g−1) and 70 to 130 Oe (5 to 13 emu g−1), respectively. Saturation magnetization of SNPs, RNPs and HNPs spans from 50 to 65 emu g−1, 12 to 60 emu g−1 and 57 to 80 emu g−1, respectively. Under AC magnetic field (522 kHz), with amplitude ranging from 70 to 310 Oe, SNPs show a strong hyperthermia effect, following HNPs with mild and RNPs with weak effects.

Maghemite–gold core–shell nanostructures (γ-Fe2O3@Au) surface-functionalized with aluminium phthalocyanine for multi-task imaging and therapy

In this study we report on the elaboration and characterization of core–shell maghemite–gold nanoparticles with the shell modulated for different thicknesses below 2 nm. Gold-shelled maghemite nanoparticles with an average core size of about 9 nm were developed using a single-step protocol involving reduction of Au3+ in the presence of citrate-coated maghemite nanoparticles. Additionally, post-functionalization of the core–shell structures with aluminium phthalocyanine was successfully accomplished, aimed at the production of a material platform for photodynamic therapy. The as-produced samples were structurally, morphologically, magnetically and optically characterized and presented long-term colloidal stability at physiological pH. Impressively, we found the as-produced samples showed good X-ray attenuation properties, making them able to be used as nanoprobes for targeted computed tomography. Moreover, in vitro nanocytotoxicity tests confirmed a superior biocompatibility of the as-produced samples, making them a very promising multi-task platform for in vivo applications.