Daniela Caruntu

Magnetic Properties of Variable-sized Fe3O4 Nanoparticles Synthesized from Non-aqueous Homogeneous Solutions of Polyols

The magnetic behaviour of well-dispersed monodisperse Fe3O4 nanoparticles with sizes varying between 6.6 and 17.8?nm prepared in a non-aqueous medium was investigated. The smaller nanocrystals exhibit superparamagnetism with the blocking temperatures increasing with the particle size, whereas the biggest particles are ferromagnetic at room temperature. The saturation magnetization values are slightly smaller than that of the bulk material, suggesting the existence of a disordered spin configuration on their surface. The thickness of the magnetically inert shell was estimated from the size variation of the magnetization at 1.9??. The dipole?dipole interactions between the particles were tuned by changing the interparticle distances, e.g. by diluting the nanopowders in a non-magnetic matrix at concentrations ranging from 0.25 to 100?wt%. As the strength of the interactions is decreased with dilution, the energy barrier is substantially lowered; this will induce a drastic decrease of both the blocking temperatures and the coercivity with decreasing concentration of the nanoparticles.

Magnetic properties of ultrafine cobalt ferrite particles

We have studied magnetic properties of a diluted system of ultrafine cobalt ferrite nanoparticles (d∼3.3 nm). From the peak of the zero-field-cooled measurements, we obtained the blocking temperature TB of about 90.5 K and it is virtually independent of the applied magnetic field up to 5 kOe. At the superparamagnetic region T>TB, the system follows the modified Curie-law variation of the magnetic susceptibility χ=χo+C/T. We observed that the saturation magnetization follows a spin-wavelike temperature dependence at temperature above 10 K. In spite of the cubic structure for cobalt ferrite, at 2 K, the reduced remanence Mr/Ms is equal to 0.46 which is close to the theoretical value of 0.5 expected for noninteracting uniaxial single-domain particles with the easy axis randomly oriented. From the ac susceptibility measurements at different frequencies, we obtained a linear dependence of the logarithm of the experimental time window τex as function of inverse blocking temperature (1/TB). The fitting results i...

Water-Dispersible Iron Oxide Magnetic Nanoparticles with Versatile Surface Functionalities

We report a simple one-pot strategy to prepare surface-function-alized, water-dispersible iron oxide nanoparticles. Small organic molecules that have desired functional groups such as amines, carboxylics, and thiols are chosen as capping agents and are injected into the reaction medium at the end of the synthesis. A diversity of functionalities are effectively introduced onto the surface of the nanoparticles with a minimal consumption of solvents and chemical resources by simply switching the capping ligand to form the ligand shell. The resulting nanocrystals are quasi-spherical and narrowly size-distributed. Energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy studies suggest a successful surface modification of iron oxide nanoparticles with selected functionalities. The colloidal stabilities are characterized by dynamic light scattering and zeta potential measurements. The results imply that functionalized nanoparticles are very stable and mostly present as individual units in buffer solutions. The pedant functional groups of the capping ligand molecules are very reactive, and their availabilities are investigated by covalently linking fluorescent dyes to the nanoparticles through the cross-linking of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The quenched quantum yield and shortened lifetime of the dyes strongly indicate a direct bonding between the functional group of the nanoparticles and the fluorescent molecules.

Gold–magnetite nanocomposite materials formed via sonochemical methods

Treatment of preformed magnetite nanoparticles with ultrasound in aqueous media with dissolved tetrachloroauric acid resulted in the formation of gold-magnetite nanocomposite materials. These materials maintained the morphology of the original magnetite particles. The loading of gold particles could be controlled by adjusting experimental parameters, including the addition of small amounts of solvent modifiers such as methanol, diethylene glycol, and oleic acid. The nanocomposite materials were magnetic and exhibited optical properties similar to pure gold nanoparticles.

Synthesis and magnetic properties of CoPt–poly(methylmethacrylate) nanostructured composite material

We have prepared nanometer-sized CoPt particles dispersed in a poly(methyl methacrylate) (PMMA) matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed in methylmethacrylate (monomer). The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a “core” material and CoPt–PMMA composite material were characterized by using energy dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction, indicating that we are able to prepare CoPt nanoparticles with <10 nm in diameter (after annealing) by employing this high temperature colloidal processing method. Magnetic in...

Fabrication of magnetic hollow silica nanospheres for bioapplications

Different kinds of nanospheres are used in magnetic nanosphere fabrication for bioapplications. In this paper, we report a successful synthesis of magnetic hollow silica nanospheres (MHSNS). The MHSNS were fabricated with a one step coating of Fe3O4 magnetic nanoparticles (NPs)(∼10nm) and silica on nanosized (20–100nm) spherical calcium carbonate (CaCO3) surface under alkaline conditions, in which the nanosized CaCO3 were used as nanotemplates and tetraethoxysilane and magnetic NPs were used as precursors. The as-synthesized nanoshperes were immersed in an acidic solution to remove nanosized CaCO3, forming MHSNS. The MHSNS were characterized by SEM, TEM, and SQUID. SEM and TEM results showed that a smooth surface of MHSNS and a thin layer of silica (∼10nm) embedded with the magnetic NPs was successfully formed. No nanosized CaCO3 nanotemplates were observed. SQUID measurement demonstrated that magnetization of MHSNS was dependent on temperature, exhibiting superparamagnetism. The MHSNS have potential appl...

Labeling Primary Amine Groups in Peptides and Proteins with N-Hydroxysuccinimidyl Ester Modified Fe3O4@SiO2 Nanoparticles Containing Cleavable Disulfide-bond Linkers

The surface of superparamagnetic silica coated iron oxide (Fe3O4@SiO2) nanoparticles was functionalized with a disulfide bond linked N-hydroxysuccinimidyl (NHS) ester group in order to develop a method for labeling primary amines in peptides/proteins. The nanoparticle labeled proteins/peptides formed after NHS ester reaction with the primary amine groups were isolated using a magnet without any additional purification step. Nanoparticle moieties conjugated to peptides/proteins were then trimmed by cleavage at the disulfide linker with a reducing agent. The labeled peptides were analyzed by LC-MS/MS to determine their sequences and the sites of NHS ester labeling. This novel approach allowed characterization of lysine residues on the solvent accessible surface of native bovine serum albumin. Low cost, rapid magnetic separation, and specificity toward primary amine groups make NHS ester coated Fe3O4@SiO2 nanoparticles a potential labeling probe to study proteins on living cell surfaces.

Towards one key to one lock: catalyst modified indium oxide nanoparticle thin film sensor array for selective gas detection

Homogeneous In2O3 nanoparticles (NPs) were self-assembled into thin film sensor arrays on a single chip, with further surface modification by noble metal catalysts. The NP film sensor arrays show clear current responses when exposed to different target gases, and both sensitivity and selectivity were greatly improved. Particularly, the sensors modified with Au, Pd, and Pt nanocatalysts demonstrated higher sensitivity to H2S, H2 and CO, respectively, making the gas discrimination direct and simple, like “one key to one lock”. The particle size dependence of the noble metal modifiers to the sensitivity was further investigated by tuning the sputtering parameters. Three different trends of sensitivities were observed, each attributed to different mechanisms. The modified nanoparticle film sensor was also fabricated on flexible substrates and the sensing performance was investigated at different bending angles.

Synthesis of magnetic porous hollow silica nanotubes for drug delivery

In this paper, we report a synthesis of magnetic porous hollow silica nanotubes (MPHSNTs) using sol-gel method. The MPHSNTs were fabricated by coating Fe3O4 nanoparticles and silica on surfactant hexadecyltrimethylammonium bromide (CTAB) modified CaCO3 nanoneedles surface under alkaline condition. CaCO3 nanoneedles and surfactant CTAB are introduced as nanotemplates to form the hollow and porous structures, respectively. After removing CTAB by calcination and etching CaCO3 nanoneedles away in diluted acetic acid, magnetic porous hollow silica nanotubes with Fe3O4 nanoparticles embedded in the silica shell were achieved. The products were characterized by scanning electron microscopy, transmission electron microscopy, and N2 adsorption-desorption isotherms. Superconducting quantum interference device measurement shows that the nanotubes exhibit superparamagnetism property at room temperature and ferromagnetism below the blocking temperature. Toxicity test was also performed for the magnetic nanocarriers, s...

Investigation of Gas-Sensing Performance of

Two forms of tin oxide (SnO2) nanoparticles (NPs) with different morphologies (small dispersed NPs and big clusters aggregated from small NPs) were synthesized via chemical solution methods and assembled into films on Si/SiO2 substrate for a comparative sensing study, which were tested for the responses to H2 S reducing gas and NO2 oxidizing gas, respectively. Similar detection limits to part per million levels H2 S reducing gas and part per billion (ppb) levels NO2 oxidizing gas were observed for both films with different morphologies at room temperature. It was found, however, that the small NP film showed higher sensitivity and detection limit to H2 S down to ppb levels after surface modification by depositing Au nanocatalysts, while SnO2 big cluster film presented better sensitivity to NO2 detection down to ppb levels with/without the nanocatalyst modification, much determined by the morphology of these two forms of NPs. The sensing mechanism is also discussed.