No abstract

No abstract

Electrochemical behavior of the bare indium-tin oxide ͑ITO͒ electrode in 1 M NaOH electrolyte has been studied in a wide range of current density and applied charge in view of its possible application as a counterelectrode in rare earth optical windows. Nature and kinetics of both cathodic and anodic processes developed on ITO depend on electrolyte composition as well as on transformations occurring with the electrode. Contribution of oxygen vacancies and ions O 2− is crucial for the electrochemical behavior of ITO. At the cathodic polarization, the electrode components are deeply reduced so that ITO is gradually and irreversibly converted to a metallic mirror with a noticeable decrease of oxygen content. At high anodic current density, the ITO electrode undergoes modifications and its conductivity decreases probably also due to the change of oxygen content in the oxides lattice. A phenomenological description of all the processes involved in ITO electrochemical performance and their reversibility is proposed and discussed. A stable operation of ITO in electrochemical devices can be achieved only in the case of usage of external RedOx dissolved in the electrolyte or deposited on the ITO electrode. Such active components could be selected from the different systems studied for flat panel displays.

No abstract

Mesoporous silicon is a biocompatible, biodegradable material that is receiving increased attention for pharmaceutical applications due to its extensive specific surface. This feature enables to load a variety of drugs in mesoporous silicon devices by simple adsorption-based procedures. In this work, we have addressed the fabrication and characterization of two new mesoporous silicon devices prepared by electrochemistry and intended for protein delivery, namely: (i) mesoporous silicon microparticles and (ii) chitosan-coated mesoporous silicon microparticles. Both carriers were investigated for their capacity to load a therapeutic protein (insulin) and a model antigen (bovine serum albumin) by adsorption. Our results show that mesoporous silicon microparticles prepared by electrochemical methods present moderate affinity for insulin and high affinity for albumin. However, mesoporous silicon presents an extensive capacity to load both proteins, leading to systems were protein could represent the major mass fraction of the formulation. The possibility to form a chitosan coating on the microparticles surface was confirmed both qualitatively by atomic force microscopy and quantitatively by a colorimetric method.Mesoporous silicon microparticles with mean pore size of 35 nm released the loaded insulin quickly, but not instantaneously. This profile could be slowed to a certain extent by the chitosan coating modification. With their high protein loading, their capacity to provide a controlled release of insulin over a period of 60-90 min, and the potential mucoadhesive effect of the chitosan coating, these composite devices comprise several features that render them interesting candidates as transmucosal protein delivery systems.

Porous silicon (porSi), which contains luminescent Si nanocrystal assemblies, is a promising semiconductor material for the photosensitized formation of singlet oxygen, 1 O 2 , for biological applications. However, because as-prepared luminescent Si nanocrystals are H-terminated and therefore hydrophobic, the first step to create a prototype of Si nanocrystalbased photosensitizer should be a modification of the Si nanocrystal surface with the aim to make it hydrophilic and able to work in a biological ambient. Such surface modification by surfactants should not, however, result in a decrease of the nanocrystals' durability that may, in principle, take place because of surfactant-induced weakening of surface tension and the consequent increase of interaction with H 2 O molecules. Surfactants should not also decrease the ability of the nanocrystals to transfer the excitation energy to acceptors (first of all molecular oxygen) on their surface. These rather contradictory tasks have been largely solved in the present work by use of nonionic surfactants physically adsorbed on the porSi surface.One of the strategic objectives of nanotechnology is the development of new materials of nanometer size that have entirely new physical properties, and, therefore, new functionality. Over the last decade, tailoring of material characteristics by size control has been demonstrated for many types of semiconductors. Optical and electronic properties of semiconductor nanocrystals can be simply engineered by changing their size and composition. When electrons and holes are squeezed into a dimension that approaches a critical size, quantum-confinement effects become apparent. This effect can be seen experimentally as a widening of the semiconductor nanocrystal bandgap.[1]

No abstract

This work aims at studying of electrochemical oxidation of porous silicon (PSi) and its behaviour in simulated body fluid (SBF). Continuing electrochemical oxidation of PSi introduces gradual changes in morphology of the porous structure and composition of PSi. As a result, interaction between this material and SBF is changed. As more oxidized is the PSi sample, slower is the dissolution process (biodegradability) and more easily it becomes covered by the calcium-phosphorous deposits from SBF (bioactivity). We observed that crystalline hydroxyapatite HA phase could be deposited in a very homogeneous manner onto OxPSi layers immersed in SBF at 36.5 o C during 30 days.