Publications

Si/SiO2 quantum dots (QDs) are novel particles with unique physicochemical properties that promote them as potential candidates for biomedical applications. Although their interaction with human cells has been poorly investigated, oxidative stress appears to be the main factor involved in the cytotoxicity of these nanoparticles. In this study, we show for the first time the influence of Si/SiO2 QDs on cellular redox homeostasis and glutathione distribution in human lung fibroblasts. The nanoparticles morphology, composition and structure have been investigated using high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. MRC-5 cells (human lung fibroblasts) were incubated with various concentrations of Si/SiO2 QDs ranging between 25 and 200 mu g/mL for up to 72 h. The results of the MTT and sulforhodamine B assays showed that exposure to QDs led to a time-dependent decrease in cell viability and biomass. The increase in reactive oxygen species (ROS) and malondialdehyde (MDA) levels together with the lower glutathione content suggested that the cellular redox homeostasis was altered. Regarding GSH distribution, the first two days of treatment resulted in a localization of GSH mainly in the cytoplasm, while at longer incubation time the nuclear/cytoplasmic ratio indicated a nuclear localization. These modifications of cell redox state also affected the redox status of proteins, which was demonstrated by the accumulation of oxidized proteins and actin S-glutathionylation. In addition, the externalization of phosphatidylserine provided evidence that apoptosis might be responsible for cell death, but necrosis was also revealed. Our results suggest that Si/SiO2 quantum dots exerted cytotoxicity on MRC-5 cells by disturbing cellular homeostasis which had an effect upon protein redox status. (C) 2014 Elsevier Ireland Ltd. All rights reserved.

We study an array of dissipative tunnel-coupled cavities, each interacting with an incoherently pumped two-level emitter. For cavities in the lasing regime, we find correlations between the light fields of distant cavities, despite the dissipation and the incoherent nature of the pumping mechanism. These correlations decay faster than any power of the distance for arrays in any dimension but become increasingly long ranged with increasing photon tunneling between adjacent cavities. The interaction-dominated and the tunneling-dominated regimes show markedly different scaling of the correlation length which always remains finite due to the finite photon trapping time. We propose a series of observables to characterize the spontaneous buildup of collective coherence in the system.

Results of a comparative study on the growth from melt by the Bridgman-Slockbarger method of metadinitrobenzene (m-DNB) and benzil (Bz) crystals in the same experimental set-up and the same experimental conditions are presented. The incorporation of an inorganic (iodine) dopant in m-DNB was analyzed in the given experimental conditions from the point of view of the solid-liquid interlace stability. The limits for a stable growth and the conditions that favor the generation of morphological instability are emphasized. These limits for m-DNB are compatible with those previously determined for Bz, and therefore, even for a high gradient concentration at the growth interface, it is possible to grow mDNB and Bz crystals in the same experimental conditions characterized by a high AT and t', The optical properties were investigated in relation with the dopant incorporation in the crystal in the mentioned experimental conditions. Effects of the dopant (m-DNB/iodine in Bz and iodine in m-ONES) on the optical band gap and optical non-linear properties of the crystals are discussed. (C) 2014 Elsevier B.V. All rights reserved

Nano- or micropowders of Eu2O3 were added to MgB2, resulting in a composition of (MgB2)(0.975)(EuO1.5)(0.025). Pristine and doped samples were prepared using spark plasma sintering and tested for (i) Vickers hardness, (ii) pH evolution in phosphate-buffered saline solution, (iii) corrosion resistance (Tafel polarization curves), (iv) cytotoxicity (in vitro tests), and (v) antibacterial activity. Eu2O3 addition influenced the investigated properties. Solutions of MgB2-based samples show a relatively high saturation pH of 8.5. This value is lower than that of solutions incubated with Mg or other Mg-based biodegradable alloys reported in the literature. MgB2-based samples have lower electro-corrosion rates than Mg. Their Vickers hardness is 6.8-10.2 GPa, and these values are higher than those of biodegradable Mg-based alloys. MgB2 has low in vitro biocompatibility, good antibacterial activity against Escherichia coli, and mild activity against Staphylococcus aureus. Our results suggest that MgB2-based materials deserve attention in biomedical applications, such as implants or sterile medical instruments. (C) 2014 Elsevier B.V. All rights reserved.

High density (above 93%) superconducting bulks of MgB2 with addition of hexagonal BN (h-BN) and cubic BN (c-BN) with compositions ((MgB2) + (BN)(x), x = 0.01, 0.03, 0.05) were obtained by ex situ spark plasma sintering. All the investigated samples have the critical temperature T-c = 38.8 K. The variation of the critical current density J(c) with the external magnetic field H for h-BN added sample is almost overlapping the J(c)(H) dependence for the pristine MgB2 sample. On the other hand, J(c) for the samples added with c-BN is larger at high magnetic fields, while the decrease of J(c) at low H is very small. At T = 20 K, a J(c) of 10(2) A cm(-2) is determined for the sample with x(c-BN) = 0.005 at H = 58 kOe, and for the sample with x(c-BN) = 0.01 at 54 kOe. Magnetic relaxation measurements indicate a significant flux pinning enhancement in MgB2 samples added with c-BN. It is proposed that the disorder at the interface caused by the convenient lattice matching relationship between the lateral plane of the MgB2 crystal prism and the face of the c-BN crystal cube is responsible for the observed vortex pinning increase.

Titanium oxide/graphene oxide nanocomposite thin films were grown by ultraviolet (UV) matrix-assisted pulsed laser evaporation (MAPLE) technique in controlled oxygen or nitrogen atmospheres. The effect of graphene oxide addition and laser-induced reduction as well as nitrogen doping on the wetting behavior and photoactive properties of titanium oxide thin films was investigated. Hydrophobic to hydrophilic conversion of titanium oxide films takes place progressively as the relative amount of graphene oxide in the MAPLE composite target increases. Nitrogen doping leads to further decrease of the static contact angle of the composite films. The photoactive properties of the synthesized materials were investigated through the evolution of contact angle under UV light irradiation. Wetting properties of both TiO2 and TiO2/GO nanocomposite thin films improved upon exposure to UV light.

Sol-gel template method has been used to prepare BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu2+ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu2+ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu2+ is a very efficient Xray phosphor the material might be used as X-ray micro-imaging detector. (C) 2014 Elsevier Ltd. All rights reserved.