Porous Silicon applications in biotechnology

Biotechnology is a field in great expansion and the continuous boost for obtaining smaller and more efficient devices stimulates the increase of interest from the research community. Nanostructured materials, and among them porous silicon (PS), appear to be good candidates for coupling with biological molecules because of their peculiar characteristics. In the case of porous silicon, the most noticeable are the very large specific area, which allows the loading of large amounts of biological material in a very small volume, and the possibility to easily tailor the pore size and morphology as function of the kind of molecules to be introduced. Besides, the proven biocompatibility and non toxicity of PS allow the development of electronic devices to be directly implanted into living organisms without risk of rejection. In this thesis we mainly focus our attention on the fabrication and characterization of a porous silicon-based potentiometric biosensor for triglycerides analysis, made of a lipase immobilized on a mesoporous Si matrix. Prototypes, realized on 1 x 1 cm n+-type silicon wafers, show a very high enzymatic activity. Moreover the properties of these biosensors have been shown to be stable in a several months time interval, clearly showing their advantages with respect to traditional triglycerides detection systems. The Michaelis Menten curve is obtained to demonstrate the absence of diffusion problems. Potentiometric measurements are also shown

Porous Silicon applications in biotechnology

Biotechnology is a field in great expansion and the continuous boost for obtaining smaller and more efficient devices stimulates the increase of interest from the research community. Nanostructured materials, and among them porous silicon (PS), appear to be good candidates for coupling with biological molecules because of their peculiar characteristics. In the case of porous silicon, the most noticeable are the very large specific area, which allows the loading of large amounts of biological material in a very small volume, and the possibility to easily tailor the pore size and morphology as function of the kind of molecules to be introduced. Besides, the proven biocompatibility and non toxicity of PS allow the development of electronic devices to be directly implanted into living organisms without risk of rejection. In this thesis we mainly focus our attention on the fabrication and characterization of a porous silicon-based potentiometric biosensor for triglycerides analysis, made of a lipase immobilized on a mesoporous Si matrix. Prototypes, realized on 1 x 1 cm n+-type silicon wafers, show a very high enzymatic activity. Moreover the properties of these biosensors have been shown to be stable in a several months time interval, clearly showing their advantages with respect to traditional triglycerides detection systems. The Michaelis Menten curve is obtained to demonstrate the absence of diffusion problems. Potentiometric measurements are also shown

Particle swarm optimization of GaAs-AlGaAS nanowire photonic crystals as two-dimensional diffraction gratings for light trapping

Semiconductor nanowire ordered arrays represent a class of bi-dimensional photonic crystals that can be engineered to obtain functional metamaterials. Here is proposed a novel approach, based on a particle swarm optimization algorithm, for using such a photonic crystal concept to design a semiconductor nanowire-based two-dimensional diffraction grating able to guarantee an in-plane coupling for light trapping. The method takes into account the experimental constraints associated to the bottom-up growth of nanowire arrays, by processing as input dataset all relevant geometrical and morphological features of the array, and returns as output the optimised set of parameters according to the desired electromagnetic functionality of the metamaterial. A case of study based on an array of tapered GaAs-AlGaAs core-shell nanowire heterostructures is discussed

Surface Nano-Patterning for the Bottom-Up Growth of III-V Semiconductor Nanowire Ordered Arrays

Ordered arrays of vertically aligned semiconductor nanowires are regarded as promising candidates for the realization of all-dielectric metamaterials, artificial electromagnetic materials, whose properties can be engineered to enable new functions and enhanced device performances with respect to naturally existing materials. In this review we account for the recent progresses in substrate nanopatterning methods, strategies and approaches that overall constitute the preliminary step towards the bottom-up growth of arrays of vertically aligned semiconductor nanowires with a controlled location, size and morphology of each nanowire. While we focus specifically on III-V semiconductor nanowires, several concepts, mechanisms and conclusions reported in the manuscript can be invoked and are valid also for different nanowire materials

A Pilot Power Plant Based on Concentrating Solar and Energy Storage Technologies for Improving Electricity Dispatch

AbstractThis paper presents the main features and the expected performance of the pilot solar power plant under construction in Ottana (Sardinia-Italy). The facility is based on a 600 kWe concentrating solar power (CSP) plant with thermal energy storage, and a 400 kWe concentrating photovoltaic (CPV) plant with electrochemical storage. The CSP plant uses linear Fresnel collectors, thermal oil as heat transfer fluid, a two-tank direct storage system and an ORC module. The CPV plant consists of 37 dual-axis trackers integrated with Sodium-Nickel batteries. The facility is characterised by the integration of different concentrating solar and storage technologies. The pilot power plant has been designed in order to produce electricity with scheduled profiles according to weather forecast

Engineering the optical reflectance of randomly arranged self-assembled semiconductor nanowires

Metasurfaces made of arrays of vertically aligned semiconductor nanowires are suitable platforms for light management in optical and photonic applications. Here we report a design approach aimed at engineering the optical behavior of semiconductor nanowire ensembles randomly displaced on the substrate, in order to enhance modulation effects in their optical reflectance response. By resorting to analytical and numerical simulations we demonstrate that the combined implementation of a multi-shell layering together with a tapered designing on the individual nanowire offer new opportunities to tailor the optical reflectance oscillations in this kind of architectures. The simulation insights were compared to experimental results reported for self-assembled GaAs nanowires and GaAs/AlGaAs core-shell nanowires. The proposed approach is especially promising for epitaxially grown semiconductor nanowires, where the suggested design modifications can be easily implemented during the nanostructure growth

Unveiling the Thermoelectric Performances of Zn1−xFexSe Nanoparticles Prepared by the Hydrothermal Method

Fe2+-doped ZnSe nanoparticles, with varying concentrations of Fe2+ dopants, were prepared by the hydrothermal method and investigated using a multi-technique approach exploiting scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy, as well as measurement of the electrical transport properties and Seebeck coefficient (S). The doped nanoparticles appeared as variable-sized agglomerates on nanocrystallites upon SEM investigation for any doping level. Combined XRD and Raman analyses revealed the occurrence of a cubic structure in the investigated samples. Electric and thermoelectric (TE) transport investigations showed an increase in TE performance with an increase in Fe atom concentrations, which resulted in an enhancement of the power factors from 13 µWm−1K−2 to 120 µWm−1K−2 at room temperature. The results were also dependent on the operating temperature. The maximum power factor of 9 × 10−3 Wm−1K−2 was achieved at 150 °C for the highest explored doping value. The possible applications of these findings were discussed

Heat-Driven Iontronic Nanotransistors

Thermoelectric polyelectrolytes are emerging as ideal material platform for self-powered bio-compatible electronic devices and sensors. However, despite the nanoscale nature of the ionic thermodiffusion processes underlying thermoelectric efficiency boost in polyelectrolytes, to date no evidence for direct probing of ionic diffusion on its relevant length and time scale has been reported. This gap is bridged by developing heat-driven hybrid nanotransistors based on InAs nanowires embedded in thermally biased Na+-functionalized (poly)ethyleneoxide, where the semiconducting nanostructure acts as a nanoscale probe sensitive to the local arrangement of the ionic species. The impact of ionic thermoelectric gating on the nanodevice electrical response is addressed, investigating the effect of device architecture, bias configuration and frequency of the heat stimulus, and inferring optimal conditions for the heat-driven nanotransistor operation. Microscopic quantities of the polyelectrolyte such as the ionic diffusion coefficient are extracted from the analysis of hysteretic behaviors rising in the nanodevices. The reported experimental platform enables simultaneously the ionic thermodiffusion and nanoscale resolution, providing a framework for direct estimation of polyelectrolytes microscopic parameters. This may open new routes for heat-driven nanoelectronic applications and boost the rational design of next-generation polymer-based thermoelectric materials

Active elderly and health-can moderate exercise improve health and wellbeing in older adults? Protocol for a randomized controlled trial

Abstract Background: Aging is marked by a progressive rise in chronic diseases with an impact on social and healthcare costs. Physical activity (PA) may soothe the inconveniences related to chronic diseases, has positive effects on the quality of life and biological rhythms, and can prevent the decline in motor functions and the consequent falls, which are associated with early death and disability in older adults. Methods: We randomized 120 over-65 males and females into groups of similar size and timing and will give each either moderate physical activity or cultural and recreational activities. Being younger than 65 years, inability to participate in physical activity for any medical reason, and involvement in a massive program of physical exercise are the exclusion criteria. The primary outcome measures are quality of life, walking speed, and postural sway. Participants are tested at baseline, post-treatment, and 6-month (24 weeks) and 12-month (48 weeks) follow-ups. Discussion: This study aims at improving the quality of life, wellness, and cognitive functioning in the elderly through a low-cost affordable program of moderate physical activity. Given the growing aging of the world population and the social and economic burden of disability in the elderly, our results might have a major impact on future practices