Ilenia G. Tredici

Overestimation of nanoparticles-induced DNA damage determined by the comet assay.

Abstract The increasing use of engineered nanoparticles (NPs) in a wide range of commercial products raises concern about the possible risks that NPs pose to human health. Many aspects of the interaction between living cells and NPs are still unclear, and a reliable assessment of NP genotoxicity would be important. One of the most common tests used for genotoxicity is the comet assay, a sensitive method measuring DNA damage in individual cells. The assay was originally developed for soluble molecules, but it is also used in the assessment of genotoxicity of NPs. However, concerns have been raised recently about the reliability of this test in the case of NPs, but no conclusive results have been presented. Using nuclei isolated from human epithelial cells incubated with NPs, we obtained clear evidence of overestimation of NP genotoxicity by the comet assay in the case of CeO2, TiO2, SiO2, and polystyrene NPs. Removal of the NPs in the cytoplasm was effective in eliminating this genotoxicity overestimation (ex post damage) and determining the actual damage produced by the NPs during incubation with the cells (ex ante damage). This method could improve significantly the determination of NP genotoxicity in eukaryotic cells.

Field Assisted Sintering Mechanisms

Field assisted sintering studies have produced a wealth of data about the densification behaviors of many powder systems. However, the sheer volume of work has not met with sufficient mechanistic descriptions of the processes in metal or ceramic systems. This fact has, and is, limiting the acceptance and widespread use of this promising technique in larger than laboratory scale manufacturing. We describe here the nature of the influences of electric fields and/or currents, changes in heating rate, and the effects of applied pressures upon ceramic and metal systems in context of the commonly accepted stages of sintering. As many of the specific mechanisms discussed have not been directly characterized within field assisted sintering studies we focus on the established theoretical underpinnings to better understand their influence and to enable definitive future experimentation on this area of research.

Feasibility of electron and hole injection in heavily doped strontium barium niobate (SBN50) Sr0.5Ba0.5Nb2O6 for thermoelectric applications

Undoped and heavily doped (K, Y, Zr, Mo) strontium barium niobate Sr0.5Ba0.5Nb2O6 (SBN50) materials have been prepared by co-precipitation. X-ray diffraction shows the formation of a single-phase product and that 10% and 12.5% of the Nb sites can be occupied by Zr and Mo, respectively. K can enter 40% of the Sr sites, while the maximum Y substitution is also around 40%. The starting stoichiometry is effective in driving the substitutions to the desired sites. X-ray Absorption Spectroscopy (XAS) at the Nb-K edge shows the presence of Nb(V) independent of doping. A pre-edge 1s-4d transition surprisingly indicates the hole injection with Y doping and the electron injection with Zr doping. Chemical reduction does not affect the stability of the structure, except for a small decrease of maximum Y solubility, while the Nb(V) oxidation state and the XAS pre-edge feature are unmodified. The oxidized samples are insulators, the reduced samples show electrical conductivity, and doping significantly enhances thermop...

Optimization of 3D ZnO brush-like nanorods for dye-sensitized solar cells

In a dye-sensitized solar cell (DSSC) the amount of adsorbed dye on the photoanode surface is a key factor that must be maximized in order to obtain enhanced DSSC performance. In this study 3D ZnO nanostructures, named brush-like, are demonstrated as alternative photoanodes. In these structures, long ZnO nanorods are covered with a metal–organic precursor, known as a layered-hydroxide zinc salt (LHZS), which is subsequently converted to crystalline ZnO using two-step annealing. The LHZS is able to easily grow on any surface, such as the ZnO nanorod surface, without needing the assistance of a seed-layer. Brush-like structures synthesized using different citrate concentrations in the growth solutions and different annealing conditions are characterized and tested as DSSC photoanodes. The best-performing structure reported in this study was obtained using the highest citrate concentration (1.808 mM) and the lowest temperature annealing condition in an oxidative environment. Conversion efficiency as high as 1.95% was obtained when these brush-like structures were employed as DSSC photoanodes. These results are extremely promising for the implementation of these innovative structures in enhanced DSSCs, as well as in other applications that require the maximization of surface area exposed by ZnO or similar semiconductors, such as gas- or bio-sensing or photocatalysis.