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Indium Arsenide is a III-V semiconductor with low electron effective mass, a small band gap, strong spin-orbit coupling, and a large g-factor. These properties and its surface Fermi level pinned in the conduction band make InAs a good candidate for developing superconducting solid-state quantum devices. Here, we report the epitaxial growth of very thin InAs layers with thicknesses ranging from 12.5 nm to 500 nm grown by Molecular Beam Epitaxy on In x Al 1-x As metamorphic buffers. Differently than InAs substrates, these buffers have the advantage of being insulating at cryogenic temperatures, which allows for multiple device operations on the same wafer and thus making the approach scalable. The structural properties of the InAs layers were investigated by high-resolution X-ray diffraction, demonstrating the high crystal quality of the InAs layers. Furthermore, their transport properties, such as total and sheet carrier concentration, sheet resistance, and carrier mobility, were measured in the van der Pauw configuration at room temperature. A simple conduction model was employed to quantify the surface, bulk, and interface contributions to the overall carrier concentration and mobility.

The growth of high-quality graphene on flat and rigid templates, such as metal thin films on insulating wafers, is regarded as a key enabler for technologies based on 2D materials. In this work, the growth of decoupled graphene is introduced via non-reducing low-pressure chemical vapor deposition (LPCVD) on crystalline Cu(111) films deposited on sapphire. The resulting film is atomically flat, with no detectable cracks or ripples, and lies atop of a thin Cu 2 O layer, as confirmed by microscopy, diffraction, and spectroscopy analyses. Post-growth treatment of the partially decoupled graphene enables full and uniform oxidation of the interface, greatly simplifying subsequent transfer processes, particularly dry-pick up - a task that proves challenging when dealing with graphene directly synthesized on metallic Cu(111). Electrical transport measurements reveal high carrier mobility at room temperature, exceeding 10 4  cm 2  V -1  s -1 on SiO 2 /Si and 10 5  cm 2  V -1  s -1 upon encapsulation in hexagonal boron nitride (hBN). The demonstrated growth approach yields exceptional material quality, in line with micro-mechanically exfoliated graphene flakes, and thus paves the way toward large-scale production of pristine graphene suitable for high-performance next-generation applications., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Human islets of Langerhans are composed mostly of glucagon-secreting α cells and insulin-secreting β cells closely intermingled one another. Current methods for identifying α and β cells involve either fixing islets and using immunostaining or disaggregating islets and employing flow cytometry for classifying α and β cells based on their size and autofluorescence. Neither approach, however, allows investigating the dynamic behavior of α and β cells in a living and intact islet. To tackle this issue, we present a machine-learning-based strategy for identification α and β cells in label-free infrared micrographs of living human islets without immunostaining. Intrinsic autofluorescence is stimulated by infrared light and collected both in intensity and lifetime in the visible range, dominated by NAD(P)H and lipofuscin signals. Descriptive parameters are derived from micrographs for ~ 10 3 cells. These parameters are used as input for a boosted decision-tree model (XGBoost) pre-trained with immunofluorescence-derived cell-type information. The model displays an optimized-metrics performance of 0.86 (i.e. area under a ROC curve), with an associated precision of 0.94 for the recognition of β cells and 0.75 for α cells. This tool promises to enable longitudinal studies on the dynamic behavior of individual cell types at single-cell resolution within the intact tissue., (© 2024. The Author(s).)

The successful trajectory of liposome-encapsulated doxorubicin (e.g., Doxil, which has been approved by the U.S. Food and Drug Administration) as an anticancer nanodrug in clinical applications is contradicted by in vitro cell viability data that highlight its reduced efficacy in promoting cell death compared with non-encapsulated doxorubicin. No reports to date have provided a mechanistic explanation for this apparently discordant evidence. Taking advantage of doxorubicin intrinsic fluorescence and time-resolved optical microscopy, we analyze the uptake and intracellular processing of liposome-encapsulated doxorubicin (L-DOX) in several in vitro cellular models. Cell entry of L-DOX was found to lead to a rapid (seconds to minutes), energy- and temperature-independent release of crystallized doxorubicin nanorods into the cell cytoplasm, which then disassemble into a pool of fibril-shaped derivatives capable of crossing the cellular membrane while simultaneously releasing active drug monomers. Thus, a steady state is rapidly established in which the continuous supply of crystal nanorods from incoming liposomes is counteracted by a concentration-guided efflux in the extracellular medium of fibril-shaped derivatives and active drug monomers. These results demonstrate that liposome-mediated delivery is constitutively less efficient than isolated drug in establishing favorable conditions for drug retention in the cell. In addition to explaining previous contradictory evidence, present results impose careful rethinking of the synthetic identity of encapsulated anticancer drugs., Competing Interests: The authors declare no competing interests., (© 2024 The Authors.)

Early diagnosis is one of the most important factors in determining the prognosis in cancer. Sensitive detection and quantification of tumour-specific biomarkers have the potential to improve significantly our diagnostic capability. Here, we introduce a triggerable aptamer-based nanostructure based on an oligonucleotide/gold nanoparticle architecture that selectively disassembles in the presence of the biomarker of interest; its optimization is based also on in-silico determination of the aptamer nucleotides interactions with the protein of interest. We demonstrate this scheme for the case of Prostate Specific Membrane Antigen (PSMA) and PSMA derived from PSMA-positive exosomes. We tested the disassembly of the system by diameter and count rate measurements in dynamic light scattering, and by inspection of its plasmon resonance shift, upon addition of PSMA, finding appreciable differences down to the sub-picomolar range; this points towards the possibility that this approach may lead to sensors competitive with diagnostic biochemical assays that require enzymatic amplification. More generally, this scheme has the potential to be applied to a broad range of pathologies with specific identified biomarkers., (© 2023. The Author(s).)

Onivyde was approved by the Food and Drug Administration (FDA) in 2015 for the treatment of solid tumors, including metastatic pancreatic cancer. It is designed to encapsulate irinotecan at high concentration, increase its blood-circulation lifetime, and deliver it to cells where it is enzymatically converted into SN-38, a metabolite with 100- to 1000-fold higher anticancer activity. Despite a rewarding clinical path, little is known about the physical state of encapsulated irinotecan within Onivyde and how this synthetic identity changes throughout the process from manufacturing to intracellular processing. Herein, we exploit irinotecan intrinsic fluorescence and fluorescence lifetime imaging microscopy (FLIM) to selectively probe the supramolecular organization of the drug. FLIM analysis on the manufacturer's formulation reveals the presence of two coexisting physical states within Onivyde liposomes: (i) gelated/precipitated irinotecan and (ii) liposome-membrane-associated irinotecan, the presence of which is not inferable from the manufacturer's indications. FLIM in combination with high-performance liquid chromatography (HPLC) and a membrane-impermeable dynamic quencher of irinotecan reveals rapid (within minutes) and complete chemical dissolution of the gelated/precipitated phase upon Onivyde dilution in standard cell-culturing medium with extensive leakage of the prodrug from liposomes. Indeed, confocal imaging and cell-proliferation assays show that encapsulated and nonencapsulated irinotecan formulations are similar in terms of cell-uptake mechanism and cell-division inhibition. Finally, 2-channel FLIM analysis discriminates the signature of irinotecan from that of its red-shifted SN-38 metabolite, demonstrating the appearance of the latter as a result of Onivyde intracellular processing. The findings presented in this study offer fresh insights into the synthetic identity of Onivyde and its transformation from production to in vitro administration. Moreover, these results serve as another validation of the effectiveness of FLIM analysis in elucidating the supramolecular organization of encapsulated fluorescent drugs. This research underscores the importance of leveraging advanced imaging techniques to deepen our understanding of drug formulations and optimize their performance in delivery applications.

Background: Labeling efficiency is a crucial parameter in fluorescence applications, especially when studying biomolecular interactions. Current approaches for estimating the yield of fluorescent labeling have critical drawbacks that usually lead them to be inaccurate or not quantitative., Results: We present a method to quantify fluorescent-labeling efficiency that addresses the critical issues marring existing approaches. The method operates in the same conditions of the target experiments by exploiting a ratiometric evaluation with two fluorophores used in sequential reactions. We show the ability of the protocol to extract reliable quantification for different fluorescent probes, reagents concentrations, and reaction timing and to optimize labeling performance. As paradigm, we consider the labeling of the membrane-receptor TrkA through 4'-phosphopantetheinyl transferase Sfp in living cells, visualizing the results by TIRF microscopy. This investigation allows us to find conditions for demanding single and multi-color single-molecule studies requiring high degrees of labeling., Conclusions: The developed method allows the quantitative determination and the optimization of staining efficiency in any labeling strategy based on stable reactions., (© 2023. BioMed Central Ltd., part of Springer Nature.)

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., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The cleaning of some wooden artefacts can be challenging due to peculiar surface roughness and/or particular finishing treatments that favour the deposition of dirt and contaminants. The most common cleaning system used by conservators is agar gel, characterized by its rigidity and brittleness, which challenges the cleaning of rough and irregular surfaces typical of most wooden artefacts. In this work, alginate crosslinked with calcium (CA) and konjac glucomannan crosslinked with borax (KGB) gels were proposed to solve this issue. They were prepared and applied to smooth- and rough-surfaced mock-ups replicating wooden musical instruments' surfaces that had been subsequently covered by artificial soiling and sweat contaminants. The mechanical properties of CA and KGB gels, including their stability over a 60-day storage time, were evaluated by a texture analyzer, while cleaning efficacy was analytically evaluated by non-invasive X-ray fluorescence mapping and profilometric investigation. CA gel appeared to have a higher tensile strength and elongation at break. KGB gel was shown to be soft and resilient, indicating its suitability for cleaning rough surfaces. After repeating the cleaning application three times on the rough-surfaced mock-ups, both the CA and KGB gels were shown to have cleaning efficacy. The results obtained with CA and KGB were compared with those from the Agar application.

The supramolecular organization of Doxorubicin (DOX) within the standard Doxoves® liposomal formulation (DOX®) is investigated using visible light and phasor approach to fluorescence lifetime imaging (phasor-FLIM). First, the phasor-FLIM signature of DOX® is resolved into the contribution of three co-existing fluorescent species, each with its characteristic mono-exponential lifetime, namely: crystallized DOX (DOX c , 0.2 ns), free DOX (DOX f , 1.0 ns), and DOX bound to the liposomal membrane (DOX b , 4.5 ns). Then, the exact molar fractions of the three species are determined by combining phasor-FLIM with quantitative absorption/fluorescence spectroscopy on DOX c , DOX f , and DOX b pure standards. The final picture on DOX® comprises most of the drug in the crystallized form (∼98%), with the remaining fractions divided between free (∼1.4%) and membrane-bound drug (∼0.7%). Finally, phasor-FLIM in the presence of a DOX dynamic quencher allows us to suggest that DOX f is both encapsulated and non-encapsulated, and that DOX b is present on both liposome-membrane leaflets. We argue that the present experimental protocol can be applied to the investigation of the supramolecular organization of encapsulated luminescent drugs/molecules all the way from the production phase to their state within living matter.

InSb nanoflags are grown by chemical beam epitaxy in regular arrays on top of Au-catalyzed InP nanowires synthesized on patterned SiO 2 /InP(111)B substrates. Two-dimensional geometry of the nanoflags is achieved by stopping the substrate rotation in the step of the InSb growth. Evolution of the nanoflag length, thickness and width with the growth time is studied for different pitches (distances in one of the two directions of the substrate plane). A model is presented which explains the observed non-linear time dependence of the nanoflag length, saturation of their thickness and gradual increase in the width by the shadowing effect for re-emitted Sb flux. These results might be useful for morphological control of InSb and other III-V nanoflags grown in regular arrays.

Graphene grown via chemical vapour deposition (CVD) on copper foil has emerged as a high-quality, scalable material, that can be easily integrated on technologically relevant platforms to develop promising applications in the fields of optoelectronics and photonics. Most of these applications require low-contaminated high-mobility graphene ( i.e. , approaching 10 000 cm 2 V -1 s -1 at room temperature) to reduce device losses and implement compact device design. To date, these mobility values are only obtained when suspending or encapsulating graphene. Here, we demonstrate a rapid, facile, and scalable cleaning process, that yields high-mobility graphene directly on the most common technologically relevant substrate: silicon dioxide on silicon (SiO 2 /Si). Atomic force microscopy (AFM) and spatially-resolved X-ray photoelectron spectroscopy (XPS) demonstrate that this approach is instrumental to rapidly eliminate most of the polymeric residues which remain on graphene after transfer and fabrication and that have adverse effects on its electrical properties. Raman measurements show a significant reduction of graphene doping and strain. Transport measurements of 50 Hall bars (HBs) yield hole mobility μ h up to ∼9000 cm 2 V -1 s -1 and electron mobility μ e up to ∼8000 cm 2 V -1 s -1 , with average values μ h ∼ 7500 cm 2 V -1 s -1 and μ e ∼ 6300 cm 2 V -1 s -1 . The carrier mobility of ultraclean graphene reaches values nearly double than those measured in graphene processed with acetone cleaning, which is the method widely adopted in the field. Notably, these mobility values are obtained over large-scale and without encapsulation, thus paving the way to the adoption of graphene in optoelectronics and photonics.

High-quality heteroepitaxial two-dimensional (2D) InSb layers are very difficult to realize because of the large lattice mismatch with other widespread semiconductor substrates. A way around this problem is to grow free-standing 2D InSb nanostructures on nanowire (NW) stems, thanks to the capability of NWs to efficiently relax elastic strain along the sidewalls when lattice-mismatched semiconductor systems are integrated. In this work, we optimize the morphology of free-standing 2D InSb nanoflags (NFs). In particular, robust NW stems, optimized growth parameters, and the use of reflection high-energy electron diffraction (RHEED) to precisely orient the substrate for preferential growth are implemented to increase the lateral size of the 2D InSb NFs. Transmission electron microscopy (TEM) analysis of these NFs reveals defect-free zinc blend crystal structure, stoichiometric composition, and relaxed lattice parameters. The resulting NFs are large enough to fabricate Hall-bar contacts with suitable length-to-width ratio enabling precise electrical characterization. An electron mobility of ∼29 500 cm 2 /(V s) is measured, which is the highest value reported for free-standing 2D InSb nanostructures in literature. We envision the use of 2D InSb NFs for fabrication of advanced quantum devices., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

We fabricate dual-gated electric double layer (EDL) field effect transistors based on InAs nanowires gated with an ionic liquid, and we perform electrical transport measurements in the temperature range from room temperature to 4.2 K. By adjusting the spatial distribution of ions inside the ionic liquid employed as gate dielectric, we electrostatically induce doping in the nanostructures under analysis. We extract low-temperature carrier concentration and mobility in very different doping regimes from the analysis of current-voltage characteristics and transconductances measured exploiting global back-gating. In the liquid gate voltage interval from -2 to 2 V, carrier concentration can be enhanced up to two orders of magnitude. Meanwhile, the effect of the ionic accumulation on the nanowire surface turns out to be detrimental to the electron mobility of the semiconductor nanostructure: the electron mobility is quenched irrespectively to the sign of the accumulated ionic species. The reported results shine light on the effective impact on crucial transport parameters of EDL gating in semiconductor nanodevices and they should be considered when designing experiments in which electrostatic doping of semiconductor nanostructures via electrolyte gating is involved.

The nanowire platform offers great opportunities for improving the quality and range of applications of semiconductor quantum wells and dots. Here, we present the self-catalyzed growth of InAs/InSb/InAs axial heterostructured nanowires with a single defect-free InSb quantum dot, on Si substrates, by chemical beam epitaxy. A systematic variation of the growth parameters for the InAs top segment has been investigated and the resulting nanowire morphology analyzed. We found that the growth temperature strongly influences the axial and radial growth rates of the top InAs segment. As a consequence, we can reduce the InAs shell thickness around the InSb quantum dot by increasing the InAs growth temperature. Moreover, we observed that both axial and radial growth rates are enhanced by the As line pressure as long as the In droplet on the top of the nanowire is preserved. Finally, the time evolution of the diameter along the entire length of the nanowires allowed us to understand that there are two In diffusion paths contributing to the radial InAs growth and that the interplay of these two mechanisms together with the total length of the nanowires determine the final shape of the nanowires. This study provides insights in understanding the growth mechanisms of self-catalyzed InSb/InAs quantum dot nanowires, and our results can be extended also to the growth of other self-catalyzed heterostructured nanowires, providing useful guidelines for the realization of quantum structures with the desired morphology and properties.

We exploited a multi-scale microscopy imaging toolbox to address some major issues related to SARS-CoV-2 interactions with host cells. Our approach harnesses both conventional and super-resolution fluorescence microscopy and easily matches the spatial scale of single-virus/cell checkpoints. After its validation through the characterization of infected cells and virus morphology, we leveraged this toolbox to reveal subtle issues related to the entry phase of SARS-CoV-2 variants in Vero E6 cells. Our results show that in Vero E6 cells the B.1.1.7 strain (aka Alpha Variant of Concern) is associated with much faster kinetics of endocytic uptake compared to its ancestor B.1.177. Given the cell-entry scenario dominated by the endosomal "late pathway", the faster internalization of B.1.1.7 could be directly related to the N501Y mutation in the S protein, which is known to strengthen the binding of Spike receptor binding domain with ACE2. Remarkably, we also directly observed the central role of clathrin as a mediator of endocytosis in the late pathway of entry. In keeping with the clathrin-mediated endocytosis, we highlighted the non-raft membrane localization of ACE2. Overall, we believe that our fluorescence microscopy-based approach represents a fertile strategy to investigate the molecular features of SARS-CoV-2 interactions with cells., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2021 The Authors.)

Research interest in indium antimonide (InSb) has increased significantly in recent years owing to its intrinsic properties and the consequent opportunities to implement next-generation quantum devices. Hence, the precise, reproducible control over morphology and crystalline quality becomes of paramount importance for a practical quantum-device technology. Here, we investigate the growth of InSb nanostructures with different morphologies on InAs stems without pre-growth efforts (patterning). InSb nanostructures such as nanowires (1D), nanoflags (2D) and nanocubes (3D) have been realized by means of Au-assisted chemical beam epitaxy by tailoring the growth parameters like growth temperature, precursor fluxes, sample rotation and substrate orientation. Through morphological and crystallographic characterization, all the as-grown InSb 2D nanostructures are found to be single-crystalline with zinc blende structure, free from any defects such as stacking faults and twin planes. The existence of two families of 2D nanostructures, characterised by an aperture angle at the base of 145° and 160°, is observed and modelled. This study provides useful guidelines for the controlled growth of high-quality InSb nanostructures with different shape.

We report results on the control of barrier transparency in InAs/InP nanowire quantum dots via the electrostatic control of the device electron states. Recent works demonstrated that barrier transparency in this class of devices displays a general trend just depending on the total orbital energy of the trapped electrons. We show that a qualitatively different regime is observed at relatively low filling numbers, where tunneling rates are rather controlled by the axial configuration of the electron orbital. Transmission rates versus filling are further modified by acting on the radial configuration of the orbitals by means of electrostatic gating, and the barrier transparency for the various orbitals is found to evolve as expected from numerical simulations. The possibility to exploit this mechanism to achieve a controlled continuous tuning of the tunneling rate of an individual Coulomb blockade resonance is discussed.

The growth mechanisms of self-catalyzed InAs/InSb axial nanowire heterostructures are thoroughly investigated as a function of the In and Sb line pressures and growth time. Some interesting phenomena are observed and analyzed. In particular, the presence of In droplet on top of InSb segment is shown to be essential for forming axial heterostructures in the self-catalyzed vapor-liquid-solid mode. Axial versus radial growth rates of InSb segment are investigated under different growth conditions and described within a dedicated model containing no free parameters. It is shown that widening of InSb segment with respect to InAs stem is controlled by the vapor-solid growth on the nanowire sidewalls rather than by the droplet swelling. The In droplet can even shrink smaller than the nanowire facet under Sb-rich conditions. These results shed more light on the growth mechanisms of self-catalyzed heterostructures and give clear route for engineering the morphology of InAs/InSb axial nanowire heterostructures for different applications.

With downscaling of electronic circuits, components based on semiconductor quantum dots are assuming increasing relevance for future technologies. Their response under external stimuli intrinsically depend on their quantum properties. Here we investigate single-electron tunneling in hard-wall InAs/InP nanowires in the presence of an off-resonant microwave drive. Our heterostructured nanowires include InAs quantum dots (QDs) and exhibit different tunnel-current regimes. In particular, for source-drain bias up to few mV Coulomb diamonds spread with increasing contrast as a function of microwave power and present multiple current polarity reversals. This behavior can be modelled in terms of voltage fluctuations induced by the microwave field and presents features that depend on the interplay of the discrete energy levels that contribute to the tunneling process.

Random assemblies of vertically aligned core-shell GaAs-AlGaAs nanowires displayed an optical response dominated by strong oscillations of the reflected light as a function of the incident angle. In particular, angle-resolved specular reflectance measurements showed the occurrence of periodic modulations in the polarization-resolved spectra of reflected light for a surprisingly wide range of incident angles. Numerical simulations allowed for identifying the geometrical features of the core-shell nanowires leading to the observed oscillatory effects in terms of core and shell thickness as well as the tapering of the nanostructure. The present results indicate that randomly displaced ensembles of nanoscale heterostructures made of III-V semiconductors can operate as optical metamirrors, with potential for sensing applications.

The p75 neurotrophin (NT) receptor (p75 NTR ) plays a crucial role in balancing survival-versus-death decisions in the nervous system. Yet, despite 2 decades of structural and biochemical studies, a comprehensive, accepted model for p75 NTR activation by NT ligands is still missing. Here, we present a single-molecule study of membrane p75 NTR in living cells, demonstrating that the vast majority of receptors are monomers before and after NT activation. Interestingly, the stoichiometry and diffusion properties of the wild-type (wt) p75 NTR are almost identical to those of a receptor mutant lacking residues previously believed to induce oligomerization. The wt p75 NTR and mutated (mut) p75 NTR differ in their partitioning in cholesterol-rich membrane regions upon nerve growth factor (NGF) stimulation: We argue that this is the origin of the ability of wt p75 NTR , but not of mut p75 NTR , to mediate immature NT (proNT)-induced apoptosis. Both p75 NTR forms support proNT-induced growth cone retraction: We show that receptor surface accumulation is the driving force for cone collapse. Overall, our data unveil the multifaceted activity of the p75 NTR monomer and let us provide a coherent interpretative frame of existing conflicting data in the literature., Competing Interests: The authors declare no conflict of interest., (Copyright © 2019 the Author(s). Published by PNAS.)

In this work, we isolate individual wurtzite InAs nanowires and fabricate electrical contacts at both ends, exploiting the single nanostructures as building blocks to realize two different architectures of conductometric sensors: (a) the nanowire is drop-casted onto-supported by-a SiO 2 /Si substrate, and (b) the nanowire is suspended at approximately 250 nm from the substrate. We test the source-drain current upon changes in the concentration of humidity, ethanol, and NO 2 , using synthetic air as a gas carrier, moving a step forward towards mimicking operational environmental conditions. The supported architecture shows higher response in the mid humidity range (50% relative humidity), with shorter response and recovery times and lower detection limit with respect to the suspended nanowire. These experimental pieces of evidence indicate a minor role of the InAs/SiO 2 contact area; hence, there is no need for suspended nanostructures to improve the sensing performance. Moreover, the sensing capability of single InAs nanowires for detection of NO 2 and ethanol in the ambient atmosphere is reported and discussed.

We demonstrate high-temperature thermoelectric conversion in InAs/InP nanowire quantum dots by taking advantage of their strong electronic confinement. The electrical conductance G and the thermopower S are obtained from charge transport measurements and accurately reproduced with a theoretical model accounting for the multilevel structure of the quantum dot. Notably, our analysis does not rely on the estimate of cotunnelling contributions, since electronic thermal transport is dominated by multilevel heat transport. By taking into account two spin-degenerate energy levels we are able to evaluate the electronic thermal conductance K and investigate the evolution of the electronic figure of merit ZT as a function of the quantum dot configuration and demonstrate ZT ≈ 35 at 30 K, corresponding to an electronic efficiency at maximum power close to the Curzon-Ahlborn limit.

The eukaryotic cell compartmentalizes into spatially confined, membrane-enclosed, intracellular structures ( e. g., organelles, endosomes, and vesicles). Here, peculiar physicochemical properties of the local environment occur and participate in the regulation of ongoing molecular processes. In spite of the huge amount of available environmental probes, experiments on subcellular structures are severely challenged by their three-dimensional (3D) movement. This bottleneck is tackled here by focusing an excitation light beam in a periodic orbit around the structure of interest. The recorded signal is used as feedback to localize the structure position at high temporal resolution: microseconds along the orbit, milliseconds between orbits. The lysosome is selected as the intracellular target, together with 6-acetyl-2-dimethylaminonaphthalene (ACDAN) as probe of the physicochemical properties of the intralysosomal environment. Generalized polarization (GP) analysis of ACDAN emission is used to get a quantitative view on intralysosomal solvent dipolar relaxation. Thus, raster image correlation spectroscopy (RICS) analysis reveals that the ACDAN GP signal is fluctuating in the micro-to-millisecond time range during natural organelle 3D trafficking. We show that ACDAN GP fluctuations are characteristic of lysosomes in living cells, are selectively abolished by lysosomal basification, and depend on metabolic energy in the form of ATP. We argue that intralysosomal ACDAN GP fluctuates according to the ongoing organelle metabolism. Indeed, we report alterations in amplitude and timing of GP fluctuations in a cellular model of lysosomal storage disorder (LSD). The strategy proposed provides insight into the elusive local environment of a trafficking lysosome and supports similar molecular investigations at the subcellular level.

With the increasing interest in the potential benefits of nanotechnologies, concern is still growing that they may present emerging risks for workers. Various strategies have been developed to assess the exposure to nano-objects and their agglomerates and aggregates (NOAA) in the workplace, integrating different aerosol measurement instruments and taking into account multiple parameters that may influence NOAA toxicity. The present study proposes a multi-metric approach for measuring and sampling NOAA in the workplace, applied to three case studies in laboratories each dedicated to materials with different shapes and dimensionalities: graphene, nanowires, and nanoparticles. The study is part of a larger project with the aim of improving risk management tools in nanomaterials research laboratories. The harmonized methodology proposed by the Organization for Economic Cooperation and Development (OECD) has been applied, including information gathering about materials and processes, measurements with easy-to-use and hand-held real-time devices, air sampling with personal samplers, and off-line analysis using scanning electron microscopy. Significant values beyond which an emission can be attributed to the NOAA production process were identified by comparison of the particle number concentration (PNC) time series and the corresponding background levels in the three laboratories. We explored the relations between background PNC and microclimatic parameters. Morphological and elemental analysis of sampled filters was done to identify possible emission sources of NOAA during the production processes: rare particles, spherical, with average diameter similar to the produced NOAA were identified in the nanoparticles laboratory, so further investigation is recommended to confirm the potential for worker exposure. In conclusion, the information obtained should provide a valuable basis for improving risk management strategies in the laboratory at work., Competing Interests: The authors declare no conflict of interest.

Subwavelength nanostructured surfaces are realized with self-assembled vertically-aligned InAs nanowires, and their functionalities as optical reflectors are investigated. In our system, polarization-resolved specular reflectance displays strong modulations as a function of incident photon energy and angle. An effective-medium model allows one to rationalize the experimental findings in the long wavelength regime, whereas numerical simulations fully reproduce the experimental outcomes in the entire frequency range. The impact of the refractive index of the medium surrounding the nanostructure assembly on the reflectance was estimated. In view of the present results, sensing schemes compatible with microfluidic technologies and routes to innovative nanowire-based optical elements are discussed., Competing Interests: The authors declare no conflict of interest.

Intracellular chloride ([Cl - ] i ) and pH (pH i ) are fundamental regulators of neuronal excitability. They exert wide-ranging effects on synaptic signaling and plasticity and on development and disorders of the brain. The ideal technique to elucidate the underlying ionic mechanisms is quantitative and combined two-photon imaging of [Cl - ] i and pH i , but this has never been performed at the cellular level in vivo. Here, by using a genetically encoded fluorescent sensor that includes a spectroscopic reference (an element insensitive to Cl - and pH), we show that ratiometric imaging is strongly affected by the optical properties of the brain. We have designed a method that fully corrects for this source of error. Parallel measurements of [Cl - ] i and pH i at the single-cell level in the mouse cortex showed the in vivo presence of the widely discussed developmental fall in [Cl - ] i and the role of the K-Cl cotransporter KCC2 in this process. Then, we introduce a dynamic two-photon excitation protocol to simultaneously determine the changes of pH i and [Cl - ] i in response to hypercapnia and seizure activity., Competing Interests: The authors declare no conflict of interest.

By a combination of UV-Vis analyses, NMR-based diffusion measurements and MD simulations we have demonstrated for the first time that the HIV-1 Tat arginine-rich peptide (Tat 11 ) is able to self-aggregate in both its fluorescently labeled and unlabeled variants. We propose Tat 11 dimerization as the dominant aggregation process and show that the associated equilibrium constant increases ten-fold by labeling with the standard TAMRA dye. Also, we extend similar conclusions to other cationic cell penetrating peptides (CPPs), such as Antennapedia (Ant) and nona-arginine (R9).

We investigate the metallic phases observed in hybrid metal-GaAs nanowire devices obtained by controlled thermal annealing of Ni/Au electrodes. Devices are fabricated onto a SiN membrane compatible with transmission electron microscopy studies. Energy dispersive X-ray spectroscopy allows us to show that the nanowire body includes two Ni-rich phases that thanks to an innovative use of electron diffraction tomography can be unambiguously identified as Ni 3 GaAs and Ni 5 As 2 crystals. The mechanisms of Ni incorporation leading to the observed phenomenology are discussed.

We investigate nanoscale local anodic oxidation (LAO) on hydrogen-intercalated graphene grown by controlled sublimation of silicon carbide (SiC). Scanning probe microscopy was used as a lithographic and characterization tool in order to investigate the local properties of the nanofabricated structures. The anomalous thickness observed after the graphene oxidation process is linked to the impact of LAO on the substrate. Micro-Raman (μ-Raman) spectroscopy was employed to demonstrate the presence of two oxidation regimes depending on the applied bias. We show that partial and total etching of monolayer graphene can be achieved by tuning the bias voltage during LAO. Finally, a complete compositional characterization was achieved by scanning electron microscopy and energy dispersive spectroscopy.

Stealth agents are extensively investigated as a means by which to prolong nanostructure residence time in the bloodstream by avoiding uptake by the reticuloendothelial system. Unfortunately, commonly used agents such as poly(ethylene glycol) can adversely impact targeting efficiency and promote immune reaction by the host organism. Therefore, there is an increasing interest in developing biocompatible, non-PEGylated organic nanostructures able to perform targeted delivery to increase the efficacy of liposomal technology. Here, a lipopeptide is presented that can be mixed with lipids commonly used in liposomal formulations in percentages ranging from 20% to 60% w/w. The resulting vesicles are thermally and chemically stable. The peptide coating limits serum-protein adsorption even upon prolonged incubation in pure serum in physiological conditions, outperforming PEGylated liposomes. This architecture can be easily modified to allow straightforward derivatization by standard bio-orthogonal conjugation. Upon derivatization with an anti-transferrin receptor aptamer, these vesicles show highly selective cellular internalization with minimal nonspecific uptake and pH-triggered doxorubicin release.

We demonstrate tunable bistability and a strong negative differential resistance in InAs/GaSb core-shell nanowire devices embedding a radial broken-gap heterojunction. Nanostructures have been grown using a catalyst-free synthesis on a Si substrate. Current-voltage characteristics display a top peak-to-valley ratio of 4.8 at 4.2 K and 2.2 at room temperature. The Esaki effect can be modulated-or even completely quenched-by field effect, by controlling the band bending profile along the azimuthal angle of the radial heterostructure. Hysteretic behavior is also observed in the presence of a suitable resistive load. Our results indicate that high-quality broken-gap devices can be obtained using Au-free growth.

Reversible photoswitching has been proposed as a way to identify molecules that are present in small numbers over a large, non-switching, background. This approach, called optical-lock-in-detection (OLID) requires the deterministic control of the fluorescence of a photochromic emitter through optical modulation between a bright (on) and a dark state (off). OLID yields a high-contrast map where the switching molecules are pinpointed, but the fractional intensities of the emitters are not returned. The present work presents a modified OLID approach (quantitative OLID or qOLID) that yields quantitative information of the switching (f SW ) and non-switching (f NS ) components. After the validation of the method with a sample dataset and image sequence, we apply qOLID to measurements in cells that transiently express the photochromic protein EYQ1. We show that qOLID is efficient in separating the modulated from the non-modulated signal, the latter deriving from background/autofluorescence or fluorophores emitting in the same spectral region. Finally, we apply qOLID to Förster (Fluorescence) Resonance Energy Transfer (FRET) imaging. We here demonstrate that qOLID is able to highlight the distribution of FRET intensity in a sample by using a photochromic donor and a non-photochromic acceptor., (© 2016 Wiley Periodicals, Inc.)

We demonstrate localization and field-effect spatial control of the plasmon resonance in semiconductor nanostructures, using scattering-type scanning near-field optical microscopy in the mid-infrared region. We adopt InAs nanowires embedding a graded doping profile to modulate the free carrier density along the axial direction. Our near-field measurements have a spatial resolution of 20 nm and demonstrate the presence of a local resonant feature whose position can be controlled by a back-gate bias voltage. In the present implementation, field-effect induces a modulation of the free carrier density profile yielding a spatial shift of the plasmon resonance of the order of 100 nm. We discuss the relevance of our electrically tunable nanoplasmonic architectures in view of innovative optoelectronic devices concepts.

We investigate light emission from nanoscale point-sources obtained in hybrid metal-GaAs nanowires embedding two sharp axial Schottky barriers. Devices are obtained via the formation of Ni-rich metallic alloy regions in the nanostructure body thanks to a technique of controlled thermal annealing of Ni/Au electrodes. In agreement with recent findings, visible-light electroluminescence can be observed upon suitable voltage biasing of the junctions. We investigate the time-resolved emission properties of our devices and demonstrate an electrical modulation of light generation up to 1 GHz. We explore different drive configurations and discuss the intrinsic bottlenecks of the present device architecture. Our results demonstrate a novel technique for the realization of fast subwavelength light sources with possible applications in sensing and microscopy beyond the diffraction limit.

The enormous wealth of information available today from optical microscopy measurements on living samples is often underexploited. We argue that spatiotemporal analysis of fluorescence fluctuations using multiple detection channels can enhance the performance of current nanoscopy methods and provide further insight into dynamic molecular processes of high biological relevance., (Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

In a living cell, the movement of biomolecules is highly regulated by the cellular organization into subcompartments that impose barriers to diffusion, can locally break the spatial isotropy, and ultimately guide these molecules to their targets. Despite the pivotal role of these processes, experimental tools to fully probe the complex connectivity (and accessibility) of the cell interior with adequate spatiotemporal resolution are still lacking. Here, we show how the heterogeneity of molecular dynamics and the location of barriers to molecular motion can be mapped in live cells by exploiting a two-dimensional (2D) extension of the pair correlation function (pCF) analysis. Starting from a time series of images collected for the same field of view, the resulting 2D pCF is calculated in the proximity of each point for each time delay and allows us to probe the spatial distribution of the molecules that started from a given pixel. This 2D pCF yields an accurate description of the preferential diffusive routes. Furthermore, we combine this analysis with the image-derived mean-square displacement approach and gain information on the average nanoscopic molecular displacements in different directions. Through these quantities, we build a fluorescence-fluctuation-based diffusion tensor that contains information on speed and directionality of the local dynamical processes. Contrary to classical fluorescence correlation spectroscopy and related methods, this combined approach can distinguish between isotropic and anisotropic local diffusion. We argue that the measurement of this iMSD tensor will contribute to advance our understanding of the role played by the intracellular environment in the regulation of molecular diffusion at the nanoscale., (Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.)