Color tuning of light-emitting-diodes by modulating the concentration of red-emitting silicon nanocrystal phosphors

Luminescent forms of nanostructured silicon have received significant attention in the context of quantum-confined light-emitting devices thanks to size-tunable emission wavelength and high-intensity photoluminescence, as well as natural abundance, low cost, and non-toxicity. Here, we show that red-emitting silicon nanocrystal (SiN) phosphors, obtained by electrochemical erosion of silicon, allow for effectively tuning the color of commercial light-emitting-diodes (LEDs) from blue to violet, magenta, and red, by coating the LED with polydimethylsiloxane encapsulating different SiN concentrations. High reliability of the tuning process, with respect to SiN fabrication and concentration, and excellent stability of the tuning color, with respect to LED bias current, is demonstrated through simultaneous electrical/optical characterization of SiN-modified commercial LEDs, thus envisaging exciting perspectives for silicon nanocrystals in the field of light-emitting applications

Microneedles for Transdermal Biosensing: Current Picture and Future Direction

A novel trend is rapidly emerging in the use of microneedles, which are a miniaturized replica of hypodermic needles with length-scales of hundreds of micrometers, aimed at the transdermal biosensing of analytes of clinical interest, e.g., glucose, biomarkers, and others. Transdermal biosensing via microneedles offers remarkable opportunities for moving biosensing technol-ogies and biochips from research laboratories to real-fi eld applications, and envisages easy-to-use point-of-care microdevices with pain-free, minimally invasive, and minimal-training features that are very attractive for both devel-oped and emerging countries. In addition to this, microneedles for trans-dermal biosensing offer a unique possibility for the development of biochips provided with end-effectors for their interaction with the biological system under investigation. Direct and effi cient collection of the biological sample to be analyzed will then become feasible in situ at the same length-scale of the other biochip components by minimally trained personnel and in a minimally invasive fashion. This would eliminate the need for blood extraction using hypodermic needles and reduce, in turn, related problems, such as patient infections, sample contaminations, analysis artifacts, etc. The aim here is to provide a thorough and critical analysis of state-of-the-art developments in this novel research trend, and to bridge the gap between microneedles and biosensors

Il concetto di marca Lifestyle nel settore del lusso.

Il nostro lavoro si prefigge di contribuire a dare una definizione più marcata del concetto di Lifestyle, specificatamente nel mondo del lusso e della moda. Un posizionamento di tipo Lifestyle, infatti, fa affidamento su elementi più astratti e ad elevato valore simbolico, come l’espressione del sé. Al contrario, le marche di tipo Attribute (un termine di nostra invenzione per indicare le marche che presentano un posizionamento opposto a quelle Lifestyle) si basano su elementi più concreti, come la storia, il patrimonio culturale, l’artigianalità e la qualità. Le marche di tipo Lifestyle, tuttavia, non appartengono necessariamente solo al mondo del lusso e della moda, difatti possono essere anche marche che fanno parte di altri settori. Ad ogni modo, per questo elaborato, abbiamo preferito soffermarci sul mercato del lusso, lasciando eventualmente ad altri il compito di approfondire la ricerca nelle sue più svariate sfaccettature

Bioresorbable Materials on the Rise: From Electronic Components and Physical Sensors to In Vivo Monitoring Systems

Over the last decade, scientists have dreamed about the development of a bioresorbable technology that exploits a new class of electrical, optical, and sensing components able to operate in physiological conditions for a prescribed time and then disappear, being made of materials that fully dissolve in vivo with biologically benign byproducts upon external stimulation. The final goal is to engineer these components into transient implantable systems that directly interact with organs, tissues, and biofluids in real-time, retrieve clinical parameters, and provide therapeutic actions tailored to the disease and patient clinical evolution, and then biodegrade without the need for device-retrieving surgery that may cause tissue lesion or infection. Here, the major results achieved in bioresorbable technology are critically reviewed, with a bottom-up approach that starts from a rational analysis of dissolution chemistry and kinetics, and biocompatibility of bioresorbable materials, then moves to in vivo performance and stability of electrical and optical bioresorbable components, and eventually focuses on the integration of such components into bioresorbable systems for clinically relevant applications. Finally, the technology readiness levels (TRLs) achieved for the different bioresorbable devices and systems are assessed, hence the open challenges are analyzed and future directions for advancing the technology are envisaged

Collagen IV-β1Integrin Regulation of Exocytotic Machinery in Pancreatic Beta-Cell Insulin Secretion

Diabetes is a prevalent metabolic disease characterized by impaired insulin secretion, action, or both. β1-integrin is a key receptor that regulates cell-ECM interactions and is important in maintaining beta-cell functions, including insulin secretion. However, little is reported about the relationship between β1-integrin and the exocytotic proteins involved in insulin secretion. This study examined the influence of ECM-mediated β1-integrin activation on exocytotic machinery involved in insulin secretion using rat insulinoma (INS-1) cells. Collagen IV (COL IV) promoted INS-1 cell adhesion, spreading, and insulin secretion. Additionally, these cells displayed changes in levels and localization of exocytotic proteins involved in insulin secretion. β1-integrin antibody blocking on cells cultured on COL IV showed significantly reduced adhesion, spreading, and insulin secretion along with reduced exocytotic protein levels. Additionally, b1-integrin blocking influenced the localization of exocytotic proteins at varied time points of glucose stimulation. These results indicate that specific ECM-integrin interactions are critical for proper beta-cell function

Controlled Microfabrication of High-Aspect-Ratio Structures in Silicon at the Highest Etching Rates: The Role of H2O2 in the Anodic Dissolution of Silicon in Acidic Electrolytes

In this work the authors report on the controlled electrochemical etching of high-aspect-ratio (from 5 to 100) structures in silicon at the highest etching rates (from 3 to 10 µm min−1) at room temperature. This allows silicon microfabrication entering a previously unattainable region where etching of high-aspect-ratio structures (beyond 10) at high etching rate (over 3 µm min−1) was prohibited for both commercial and research technologies. Addition of an oxidant, namely H2O2, to a standard aqueous hydrofluoric (HF) acid electrolyte is used to dramatically change the stoichiometry of the silicon dissolution process under anodic biasing without loss of etching control accuracy at the higher depths (up to 200 µm). The authors show that the presence of H2O2 reduces the valence of the dissolution process to 1, thus rendering the electrochemical etching more effective, and catalyzes the etching rate by opening a more efficient path for silicon dissolution with respect to the well-known Gerischer mechanism, thus increasing the etching speed at both shorter and higher depths

Flexible Polydimethylsiloxane Foams Decorated with Multiwalled Carbon Nanotubes Enable Unprecedented Detection of Ultralow Strain and Pressure Coupled with a Large Working Range

Low-cost piezoresistive strain/pressure sensors with large working range, at the same time able to reliably detect ultralow strain (≤0.1%) and pressure (≤1 Pa), are one of the challenges that have still to be overcome for flexible piezoresistive materials toward personalized health-monitoring applications. In this work, we report on unprecedented, simultaneous detection of ultrasmall strain (0.1%, i.e., 10 μm displacement over 10 mm) and subtle pressure (20 Pa, i.e., a force of only 2 mN over an area of 1 cm2) in compression mode, coupled with a large working range (i.e., up to 60% for strain - 6 mm in displacement - and 50 kPa for pressure) using piezoresistive, flexible three-dimensional (3D) macroporous polydimethylsiloxane (pPDMS) foams decorated with pristine multiwalled carbon nanotubes (CNTs). pPDMS/CNT foams with pore size up to 500 μm (i.e., twice the size of those of commonly used foams, at least) and porosity of 77%, decorated with a nanostructured surface network of CNTs at densities ranging from 7.5 to 37 mg/cm3 are prepared using a low-cost and scalable process, through replica molding of sacrificial sugar templates and subsequent drop-casting of CNT ink. A thorough characterization shows that piezoresistive properties of the foams can be finely tuned by controlling the CNT density and reach an optimum at a CNT density of 25 mg/cm3, for which a maximum change of the material resistivity (e.g., ρ0/ρ50 = 4 at 50% strain) is achieved under compression. Further static and dynamic characterization of the pPDMS/CNT foams with 25 mg/cm3 of CNTs highlights that detection limits for strain and pressure are 0.03% (3 μm displacement over 10 mm) and 6 Pa (0.6 mN over an area of 1 cm2), respectively; moreover, good stability and limited hysteresis are apparent by cycling the foams with 255 compression-release cycles over the strain range of 0-60%, at different strain rates up to 10 mm/min. Our results on piezoresistive, flexible pPDMS/CNT foams pave the way toward breakthrough applications for personalized health care, though not limited to these, which have not been fully addressed to date with flexible strain/stress sensors

Structural and thermoanalytical characterization of 3D porous PDMS foam materials: The effect of impurities derived from a sugar templating process

Polydimethylsiloxane (PDMS) polymers are extensively used in a wide range of research and industrial fields, due to their highly versatile chemical, physical, and biological properties. Besides the different two-dimensional PDMS formulations available, three-dimensional PDMS foams have attracted increased attention. However, as-prepared PDMS foams contain residual unreacted low molecular weight species that need to be removed in order to obtain a standard and chemically stable material for use as a scaffold for different decorating agents. We propose a cleaning procedure for PDMS foams obtained using a sugar templating process, based on the use of two different solvents (hexane and ethanol) as cleaning agents. Thermogravimetry coupled with Fourier Transform Infrared Spectroscopy (TG-FTIR) for the analysis of the evolved gasses was used to characterize the thermal stability and decomposition pathway of the PDMS foams, before and after the cleaning procedure. The results were compared with those obtained on non-porous PDMS bulk as a reference. Micro-CT microtomography and scanning electron microscopy (SEM) analyses were employed to study the morphology of the PDMS foam. The thermogravimetric analysis (TGA) revealed a different thermal behaviour and crosslinking pathway between bulk PDMS and porous PDMS foam, which was also influenced by the washing process. This information was not apparent from spectroscopic or morphological studies and it would be very useful for planning the use of such complex and very reactive systems

Vapor‐Phase Synthesis of Molecularly Imprinted Polymers on Nanostructured Materials at Room‐Temperature

Molecularly imprinted polymers (MIPs) have recently emerged as robust and versatile artificial receptors. MIP synthesis is carried out in liquid phase and optimized on planar surfaces. Application of MIPs to nanostructured materials is challenging due to diffusion-limited transport of monomers within the nanomaterial recesses, especially when the aspect ratio is >10. Here, the room temperature vapor-phase synthesis of MIPs in nanostructured materials is reported. The vapor phase synthesis leverages a >1000-fold increase in the diffusion coefficient of monomers in vapor phase, compared to liquid phase, to relax diffusion-limited transport and enable the controlled synthesis of MIPs also in nanostructures with high aspect ratio. As proof-of-concept application, pyrrole is used as the functional monomer thanks to its large exploitation in MIP preparation; nanostructured porous silicon oxide (PSiO2) is chosen to assess the vapor-phase deposition of PPy-based MIP in nanostructures with aspect ratio >100; human hemoglobin (HHb) is selected as the target molecule for the preparation of a MIP-based PSiO2 optical sensor. High sensitivity and selectivity, low detection limit, high stability and reusability are achieved in label-free optical detection of HHb, also in human plasma and artificial serum. The proposed vapor-phase synthesis of MIPs is immediately transferable to other nanomaterials, transducers, and proteins