Vanadium oxide nanoparticles as optical sensors of cysteine.

We report on the synthesis of vanadium oxide nanoparticles using the laser ablation in solution technique. The particles were characterized by dynamic light scattering-DLS, transmission electron microscopy-TEM, X-ray diffraction-XRD, X-ray photoelectron spectroscopy-XPS and UV-Vis optical spectroscopy. The oxide nanoparticles are mainly composed of tetragonal V2O5, a semiconductor with a 2.2 eV band gap. The interaction of the nanoparticles with cysteine, a very important aminoacid present in proteins, was studied. Upon reaction with cysteine, the bandgap of the nanoparticles shifts to the ultraviolet region at 2.87 eV. This color change from yellow to transparent can be used for selective cysteine sensing. Additionally, the intervalence band of the optical absorption spectra shows capability for cysteine sensing in the microM range.

Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces.

In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface.

Synthesis and characterization of disordered layered silica obtained by selective leaching of octahedral sheets from chrysotile and phlogopite structures.

Natural chrysotile fibers and pegmatitic phlogopite were acid-leached under controlled conditions. The resulting products were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, (29)Si nuclear magnetic resonance, transmission electron microscopy, and selected area electron diffraction. The leached products derived of the two clays are similar, consisting of layered hydrated disordered silica with a "distorted" structure resembling the silicate layer existing in the original minerals. A simple model of the "disordered" silica structure is presented.

Tuning Fe3O4 nanoparticle dispersion through pH in PVA/guar gum/electrospun membranes.

Polyvinyl Alcohol (PVA)/guar gum (GG) membranes with different loads of paramagnetic iron oxide Fe3O4 nanoparticles were successfully electrospun using both non-alkaline and alkaline stock solutions. The nanoparticle homogeneity distribution was clearly enhanced in fibers obtained from alkaline stock solutions. This is mainly due to the interaction between GG and the metallic ion, which also leads to further dispersion of remained uncoated nanoparticles in the mixture. It was also noticed that GG favors nanoparticle stability in the mixture and contributes to nanoparticle encapsulation. X-ray results showed that all membranes were semi-crystalline. FTIR-ATR spectra showed that Fe-O absorption band intensity improved with increasing nanoparticle load, reaching saturation at 3.5mg/ml Fe3O4 concentration under alkaline conditions. VSM analyses showed that the nanoparticles are paramagnetic and were successfully incorporated by the fibers. In vitro biocompatibility tests using L929 cells indicates adequate levels of cytotoxicity and cell adhesion/proliferation assays for both membranes obtained from non-alkaline and alkaline stock solutions. Therefore, they have potential for biomedical applications as biodegradable wound dressing.

Ferromagnetism induced by oxygen and cerium vacancies above the percolation limit in CeO2.

We studied the structural, chemical and magnetic properties of non-doped ceria (CeO(2)) thin films electrodeposited on silicon substrates. Experimental results confirm that the observed room temperature ferromagnetism is driven by both cerium and oxygen vacancies. We investigated ceria films presenting vacancy concentrations well above the percolation limit. Irradiation experiments with neon ions were employed to generate highly oxygen defective CeO(2-δ) structures. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectroscopy were used to estimate the concentration of Ce(3+) sites in the films, which can reach up to 50% of Ce(3+) replacing Ce(4+), compared to a stoichiometric CeO(2) structure. Despite the increment of structural disorder, we observe that the saturation magnetization continuously increases with Ce(3+) concentration. Our experiments demonstrate that the ferromagnetism observed in ceria thin films, highly disordered and oxygen-deficient, preserving the fluorite-type structure only in a nanometer scale, remains intrinsically stable at room temperature.