Morphological, optical and photovoltaic characteristics of MoSe2/SiOx/Si heterojunctions.

This work reports the effect of different processing parameters on the structural and morphological characteristics of MoSe2 layers grown by chemical vapour deposition (CVD), using MoO3 and Se powders as solid precursors. It shows the strong dependence of the size, shape and thickness of the MoSe2 layers on the processing parameters. The morphology of the samples was investigated by field emission scanning electron microscopy (FESEM) and the thickness of the deposited layers was determined by atomic force microscopy (AFM). Raman and photoluminescence (PL) spectroscopies were used to confirm the high quality of the MoSe2 layers. Surface composition was examined by photoelectron spectroscopy (XPS). Moreover, the MoSe2/SiOx/Si heterojunctions exhibit diode behaviour, with a rectification ratio of 10, measured at ±2.0 V, which is due to the p-i-n heterojunctions formed at the p-Si/SiOx/MoSe2 interface. A photovoltaic effect was observed with a short circuit current density (Jsc), open circuit voltage (VOC) and efficiency of -0.80 mA/cm2, 1.55 V and 0.5%, respectively. These results provide a guide for the preparation of p-i-n heterojunctions based on few-layer MoSe2 with improved photovoltaic response.

The molecular mechanism of Nystatin action is dependent on the membrane biophysical properties and lipid composition.

Nystatin (Nys) is a pore forming broad-spectrum and efficient antifungal drug with significant toxicity in mammalian organisms. In order to develop a non-toxic and more effective Nys formulation, its molecular mechanism of action at the cell membrane needs to be better understood. It is widely accepted that Nys activity and toxicity depend on the presence and type of membrane sterols. Taking advantage of multiple biophysical methodologies, we now show that the formation and stabilization of Nys aqueous pores, which are associated with Nys cytotoxicity, occur in the absence of membrane sterols. Our results suggest that the Nys mechanism of action is driven by the presence of highly ordered membrane domains capable of stabilizing the Nys oligomers. Moreover, Nys pore formation is accompanied by strong Nys-induced membrane reorganization that depends on membrane lipid composition and seems to underlie the Nys cytotoxic effect. Accordingly, in membranes enriched in a gel-phase forming phospholipid, Nys incorporates within the phospholipid-enriched gel domains, where it forms pores able to expand the gel domains. In contrast, in membranes enriched in gel domain forming sphingolipids, Nys-induced pore formation occurs through the destabilization of the gel phase. These results show that the Nys mechanism of action is complex and not only dependent on membrane sterols, and provide further insight into the molecular details governing Nys activity and toxicity.

Carbon disulfide mediated self-assembly of Laccase and iron oxide nanoparticles on gold surfaces for biosensing applications.

A simple one-step methodology was explored to prepare enzyme-modified nanostructured electrodes for the development of biosensing interfaces. Magnetite type nanoparticles conjugated with Laccase were immobilized on gold surfaces. This approach relies on the reaction between carbon disulfide and amine groups of biomolecules to form dithiocarbamate (DTC) moieties, as well as on the strong affinity between sulfur species and metals. Special emphasis was given to demonstrate DTC formation in aqueous solution and further attachment to iron oxide nanoparticles and to gold electrodes. UV-visible spectroscopy confirmed the functionalization of nanoparticles by DTC using a model secondary amine (N-hexylmethylamine). The direct attachment of modified iron oxide nanoparticles (with ca. 20 or 40nm mean sizes) to gold electrodes was investigated using the hormone epinephrine, with well-known electrochemical properties. A high amount of immobilized epinephrine and a facilitated redox conversion was observed for modified electrodes containing iron oxide nanoparticles. The success of this simple and robust method was confirmed by X-ray photoelectronic spectroscopy. Finally, the catalytic activity of modified gold with iron oxide nanoparticles and Laccase was evaluated toward 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid diammonium salt (ABTS). Chronoamperometric studies revealed a significant catalytic activity of immobilized Laccase in the presence of the nanoparticles, in particular for the largest ones (40nm), with a sensitivity for ABTS oxidation of 100mAM-1cm-2.

Potential Modulation on Total Internal Reflection Ellipsometry.

Electrochemical-total internal reflection ellipsometry (EC-TIRE) has been proposed as a technique to observe the redox reactions on the electrode surface due to its high phase sensitivity to the electrolyte/electrode interface. In this paper, we mainly focus on the influence of the potential modulation on the TIRE response. The analysis suggests that both dielectric constant variation of gold and the electric double layer transformation would modulate the reflection polarization of the surface. For a nonfaradaic process, the signal of TIRE would be proportional to the potential modulation. To testify the analysis, linear sweep voltammetry and open circuit measurement have been performed. The results strongly support the system analysis.

Phospholipid/cholesterol/decanethiol mixtures for direct assembly of immunosensing interfaces.

In this work, a simple yet robust method to prepare lipid-based biosensing interfaces on gold using common lipids (a phospholipid and cholesterol) and an alkanethiol is reported. The lipids were carefully chosen to tailor the biophysical properties of the bilayer. The simplicity of the method relies on the incorporation of a small percentage of decanethiol in the lipid vesicles for a direct formation of a thiol-linked supported lipid bilayer, which is advantageous in several respects. It prevents the use of specially synthesized thiolipids and preserves the natural fluidity and dynamics of the lipids. As a consequence the whole arrangement is extremely stable regarding ionic strength changes and solution flow during surface plasmon resonance experiments. Moreover, we show that this interface is very effective on suppressing the nonspecific adsorption of proteins on the surface, and enables the covalent attachment of the recognition antibody. The subsequent detection of specific interaction toward antigen was monitored in real-time by SPR and confirmed by ellipsometric measurements. This lipid-based biosensing platform is versatile and can be adapted to the biorecognition reaction of interest.

Studies on the electrochemical growth of (Per)2[Au(mnt)2].

The first stages of the electrocrystallization of (Per)(2)[Au(mnt)(2)] salt from dichloromethane on gold, platinum, and highly orientated pyrolytic graphite (HOPG) were investigated by cyclic voltammetry, atomic force microscopy, and X-ray photoelectron spectroscopy in order to understand the determinant factors for nucleation and crystal growth. The crystal growth occurs from adsorbed films of dithiolate on gold or platinum and of perylene on HOPG, after homogeneous nucleation, and it is controlled by the low diffusion of the species toward the growing surface.

Criptorquidia: ventajas de la cirugia temprana. / Cryptorchism: advantages of early surgery

Este trabajo informa la exeperiencia en el manejo de la criptorquidia con orquidopexia en ninos muy variadas edades.Se consideran especialmente las dificultades quirurgicas en relacion a la edad en que son intervenidos los pacientes y se senalan algunas de las complicaciones frequentes postoperatorias, sobre todo, las referentes a la involucion testicular.Se hace enfasis en la cirugia temprana, sobre todo por riesgo de atrofia testicular pero tambien por las difucultades tecnicas inherentes y mucho mayores conforme avanza la edad