Gotowa bibliografia na temat „Optical transduction techniques”

The manipulation of light via nanoengineered surfaces has excited the optical community in the past few decades. Among the many applications enabled by nanophotonic devices, sensing has stood out due to their capability of identifying miniscule refractive index changes. In particular, when free-space propagating light effectively couples into subwavelength volumes created by nanostructures, the strongly-localized near-fields can enhance light’s interaction with matter at the nanoscale. As a result, nanophotonic sensors can non-destructively detect chemical species in real-time without the need of exogenous labels. The impact of such nanophotonic devices on biochemical sensor development became evident as the ever-growing research efforts in the field started addressing many critical needs in biomedical sciences, such as low-cost analytical platforms, simple quantitative bioassays, time-resolved sensing, rapid and multiplexed detection, single-molecule analytics, among others. In this review, the optical transduction methods used to interrogate optical resonances of nanophotonic sensors will be highlighted. Specifically, the optical methodologies used thus far will be evaluated based on their capability of addressing key requirements of the future sensor technologies, including miniaturization, multiplexing, spatial and temporal resolution, cost and sensitivity.

This communication aims at discussing strategies based on developments from nanotechnology focused on the next generation of sequencing (NGS). In this regard, it should be noted that even in the advanced current situation of many techniques and methods accompanied with developments of technology, there are still existing challenges and needs focused on real samples and low concentrations of genomic materials. The approaches discussed/described adopt spectroscopical techniques and new optical setups. PCR bases are introduced to understand the role of non-covalent interactions by discussing about Nobel prizes related to genomic material detection. The review also discusses colorimetric methods, polymeric transducers, fluorescence detection methods, enhanced plasmonic techniques such as metal-enhanced fluorescence (MEF), semiconductors, and developments in metamaterials. In addition, nano-optics, challenges linked to signal transductions, and how the limitations reported in each technique could be overcome are considered in real samples. Accordingly, this study shows developments where optical active nanoplatforms generate signal detection and transduction with enhanced performances and, in many cases, enhanced signaling from single double-stranded deoxyribonucleic acid (DNA) interactions. Future perspectives on miniaturized instrumentation, chips, and devices aimed at detecting genomic material are analyzed. However, the main concept in this report derives from gained insights into nanochemistry and nano-optics. Such concepts could be incorporated into other higher-sized substrates and experimental and optical setups.

Sensing biological agents at the genomic level, while enhancing the response time for biodetection over commonly used, optics-based techniques such as nucleic acid microarrays or enzyme-linked immunosorbent assays (ELISAs), is an important criterion for new biosensors. Here, we describe the successful detection of a 35-base, single-strand nucleic acid target by Hall-based magnetic transduction as a mimic for pathogenic DNA target detection. The detection platform has low background, large signal amplification following target binding and can discriminate a single, 350 nm superparamagnetic bead labeled with DNA. Detection of the target sequence was demonstrated at 364 pM (<2 target DNA strands per bead) target DNA in the presence of 36 μM nontarget (noncomplementary) DNA (<10 ppm target DNA) using optical microscopy detection on a GaAs Hall mimic. The use of Hall magnetometers as magnetic transduction biosensors holds promise for multiplexing applications that can greatly improve point-of-care (POC) diagnostics and subsequent medical care.

Optogenetics has revolutionized the study of functional neuronal circuitry (Boyden ES, Zhang F, Bamberg E, Nagel G, Deisseroth K. Nat Neurosci 8: 1263–1268, 2005; Deisseroth K. Nat Methods 8: 26–29, 2011). Although these techniques have been most successfully implemented in rodent models, they have the potential to be similarly impactful in studies of nonhuman primate brains. Common marmosets ( Callithrix jacchus) have recently emerged as a candidate primate model for gene editing, providing a potentially powerful model for studies of neural circuitry and disease in primates. The application of viral transduction methods in marmosets for identifying and manipulating neuronal circuitry is a crucial step in developing this species for neuroscience research. In the present study we developed a novel, chronic method to successfully induce rapid photostimulation in individual cortical neurons transduced by adeno-associated virus to express channelrhodopsin (ChR2) in awake marmosets. We found that large proportions of neurons could be effectively photoactivated following viral transduction and that this procedure could be repeated for several months. These data suggest that techniques for viral transduction and optical manipulation of neuronal populations are suitable for marmosets and can be combined with existing behavioral preparations in the species to elucidate the functional neural circuitry underlying perceptual and cognitive processes.

Designed fluorescent indicators are the basis for a major new technique in cell physiology, the quantitative measurement and dynamic imaging of intracellular concentrations of important ions and messengers such as Ca2+, Na+, H+, and adenosine 3',5'-cyclic monophosphate. Molecular engineering has now produced indicators with quite good selectivity and sensitivity for these analytes. In many cases, these probes can be introduced into large populations of cells by means of membrane-permeant chemical derivatives, so that the plasma membrane need never be disrupted or physically breached at any point. Like many other optical microscopic techniques, fluorescent indicators are readily applied to study living cells and tissues, with an unparalleled combination of spatial and temporal resolution. They offer one of the few methods for continuous nondestructive monitoring of dynamic intracellular biochemistry and signal transduction in single cells or subregions of cells.

Optofluidics represents the interaction of light and fluids on a chip that integrates microfluidics and optics, which provides a promising optical platform for manipulating and analyzing fluid samples. Recent years have witnessed a substantial growth in optofluidic devices, including the integration of optical and fluidic control units, the incorporation of diverse photonic nanostructures, and new applications. All these advancements have enabled the implementation of optofluidics with improved performance. In this review, the recent advances of fabrication techniques and cutting-edge applications of optofluidic devices are presented, with a special focus on the developments of imaging and sensing. Specifically, the optofluidic based imaging techniques and applications are summarized, including the high-throughput cytometry, biochemical analysis, and optofluidic nanoparticle manipulation. The optofluidic sensing section is categorized according to the modulation approaches and the transduction mechanisms, represented by absorption, reflection/refraction, scattering, and plasmonics. Perspectives on future developments and promising avenues in the fields of optofluidics are also provided.

With the rapid developments of commercial demands, a majority of advanced researches have been investigated for the applications of underwater wireless sensor (WSN) networks. Recently optical communication has been considered for underwater wireless sensor network. An experimental set-up for testing optical communication underwater has been provided and designed in present papers to maximize the energy coupled from these displacements to the transduction mechanism that converts the mechanical energy into electrical. The true case has been considered by measuring diffuse attenuation coefficients in different seas. One stand out potential optical communication method, Visible Light Communication (VLC) has been talked and several communication methods are compared from many points of view, for example attenuation in salt water. The evaluation of modulation techniques for underwater wireless optical communications has been displayed, and further how the data collection and storage with an underwater WSN is introduced. In this paper current researches for an (UWSN) based on optical communication are studied, in particular the potential VLC method and comparisons of VLC with other optical communication approaches. Underwater challenges would be analyzed by comparing a sort of communication methods, applied in underwater. Future work will be developed at last.

Sepsis is defined as a systemic inflammatory dysfunction strictly associated with infectious diseases, which represents an important health issue whose incidence is continuously increasing worldwide. Nowadays, sepsis is considered as one of the main causes of death that mainly affects critically ill patients in clinical settings, with a higher prevalence in low-income countries. Currently, sepsis management still represents an important challenge, since the use of traditional techniques for the diagnosis does not provide a rapid response, which is crucial for an effective infection management. Biosensing systems represent a valid alternative due to their characteristics such as low cost, portability, low response time, ease of use and suitability for point of care/need applications. This review provides an overview of the infectious agents associated with the development of sepsis and the host biomarkers suitable for diagnosis and prognosis. Special focus is given to the new emerging biosensing technologies using electrochemical and optical transduction techniques for sepsis diagnosis and management.

The mammalian hippo signalling pathway controls cell proliferation and apoptosis via transcriptional co-activators YAP and TAZ, and as such is a key regulator of organ and tissue growth. Multiple cellular components converge in this pathway, including the actin cytoskeleton, which is required for YAP/TAZ activity. The precise mechanism by which the mechanical actomyosin network regulates Hippo signalling, however, is unknown. Optical methods provide a non-invasive way to image and study the biomechanics of cells. In the past two decades, super-resolution fluorescence microscopy techniques that break the diffraction limit of light have come to the fore, enabling visualisation of intracellular detail at the nanoscale level. Optical trapping, on the other hand, allows precise control of micron-sized objects such as cells. Here, super resolution structured illumination microscopy (SIM) and elastic resonator interference stress microscopy (ERISM) were used to investigate a potential role for the FERM-domain protein FRMD6, or Willin, in the mechanical control of the Hippo pathway in a neuronal cell model. A double optical trap was also integrated with the Nikon-SIM with the aim of cell stretching. Willin expression was shown to modify the morphology, neuronal differentiation, actin cytoskeleton and forces of SH-SY5Y cells. Optical trapping from above the SIM objective, however, was demonstrated to be ineffective for manipulation of adherent cells. The results presented here indicate a function for Willin in the assembly of actin stress fibres that may be the result of an interaction with the Hippo pathway regulator AMOT. Further investigation, for example by direct cell stretching, is required to elucidate the exact role of Willin in the mechanical control of YAP/TAZ.

Dans un monde de plus en plus pollué par l'activité industrielle, la détection des espèces gazeuses nocives dans l'atmosphère est d'une importance essentielle. Le marché des capteurs de gaz est déjà bien développé, avec la présence de diverses technologies et principes de détection, chacune présentant des avantages et des inconvénients intrinsèques. Dans le cadre de cette thèse, un alliage entre deux ou plusieurs technologies de détection typiquement utilisées de façon autonome a été visée, afin d'améliorer les performances globales des systèmes capteurs ainsi formées. A ce fin, nous avons conçu et étudié des dispositifs capteurs basées sur la transduction optique, couplée à un matériau sensible au gaz cible à détecter. Plus précisément, nous avons intégré pour la première fois un matériau catalyseur pouvant accélérer le taux d'oxydation des espèces chimiques (tel le monoxyde de carbone ou l'hydrogène) avec une architecture optique capable d'absorber la chaleur cédée lors de cette oxydation. L'augmentation de température occasionnée est traduite en une variation d'intensité lumineuse constituante le signal de sortie du capteur. Les travaux effectués sur les mesures de la dispersion thermique et chromatique de l'indice de réfraction des matériaux constituant le transducteur optique par des techniques d'optique guidé, ellipsométrie et des techniques photométriques sont présentés. Le sondage par moyen optique des propriétés électriques des matériaux semiconducteurs a également été étudié, y compris les variations de ces propriétés en présence des gaz oxydants, réducteurs et combustibles
In a world suffering from increasing air pollution due to spiraling industrial activity, the detection of toxic gasses in the atmosphere is of paramount importance. The gas detector market is already well developed, and features a wide variety of detection technologies and techniques, each presenting its own set of intrinsic advantages and drawbacks. In this thesis, a combination of two or more technologies typically used independently has been studied in order to improve the global performances of gas detection systems. To this length, we have conceived and studied detector architectures based upon optical transduction systems, coupled with a material presenting a specific sensitivity to the target gas. More precisely, we have for the first time integrated a catalyst designed to accelerate the oxidation rate of chemical species (such as carbon monoxide or hydrogen) with an optical component capable of absorbing the heat generated by the oxidation reaction. The associated increase in temperature is translated to a variation of the optical intensity comprising the exit signal of the detector. The work carried out measuring the chromatic and temperature dispersion of the refractive index of the materials comprising the optical transduction component by guided mode techniques, ellipsometry and photometric techniques is presented. The optical probing of the electrical properties of semiconductor materials has also been studied, including the variations of these properties following interactions with oxidizing, reducing, or combustible gasses

Ce manuscrit détaille le développement d'un montage de pince optique permettant d'étudier les propriétés mécaniques des cellules endothéliales, impliquées dans le développement de l'athérosclérose. Le but est de déterminer les propriétés viscoélastiques des cellules, et de suivre la propagation d’une contrainte mécanique au sein de la cellule. Cette contrainte mécanique est appliquée via une bille liée à la membrane de la cellule et soumise à un piège optique.Le dispositif réalisé combine le piégeage optique et la microscopie à contraste de phase, permettant d'exercer une force tout en imageant les cellules via le même objectif de microscope. L'originalité du montage de pince optique repose sur la détection du signal rétrodiffusé par la bille piégée, dans un plan conjugué du plan focal arrière de l'objectif, afin de mesurer la position relative de la bille par rapport au piège.Une part importante de ce travail a consisté à comprendre l'allure du signal détecté présentant un système d'interférences en anneaux, et à l’expliquer par un modèle simple. Ce modèle a permis de comprendre la présence d’artefacts de mesure de position dus à la superposition de l'anneau de phase sur la figure d’interférence. Pour y remédier, l'anneau de phase est déporté dans un plan conjugué intervenant uniquement dans l'imagerie de l'échantillon.La figure d'interférence présente un atout majeur : elle donne accès à la hauteur précise de la bille piégée, généralement difficile à mesurer. Cette information est nécessaire pour calibrer la constante de raideur du piège optique à la hauteur des cellules, que ce soit par l'analyse de la densité spectrale de puissance du mouvement brownien de la bille piégée ou par sa réponse à un échelon de position du piège. Ces deux méthodes de calibration, ainsi que l'application du théorème d’équipartition et l'analyse par inférence bayésienne, ont été mises en œuvre. Tous les résultats s'avèrent en bon accord. La calibration complète du dispositif en fait un outil prêt à l'emploi pour exercer des forces locales contrôlées en direction et en amplitude sur les cellules
This manuscript details the development of an optical tweezer setup to study the mechanical properties of endothelial cells, involved in the development of atherosclerosis. The goal is to determine the viscoelastic properties of the cells, and to follow the propagation of the mechanical constraint inside the cell. This mechanical constraint is applied via a bead attached to the cell membrane and subjected to an optical trap.The setup built combines optical trapping with phase contrast microscopy, to apply a force while imaging the cells with the same microscope objective. The originality of the optical tweezer setup relies on the detection of the signal backscattered by the trapped bead, in a plane conjugate to the back focal plane of the objective, in order to measure the relative position of the bead with respect to the center of the trap.An important part of this work was dedicated to the understanding of the detected signal presenting an interference pattern with rings, explained by a simple model. This model provides an explanation for the position measurement artifacts arising from the superposition of the phase ring and the interference pattern. To solve the problem, the phase ring was moved in a conjugate plane involved only in the imaging path of the sample.The interference pattern has the main advantage of giving access to the precise height of the trapped bead, usually difficult to measure. This information is necessary to calibrate the optical trap stiffness at the height of the cells, either by the power spectrum analysis of the Brownian motion of the trapped bead, or by its response to a step motion of the trap. These two calibration methods, along with the application of the equipartition theorem and Bayesian inference analysis, were implemented and their results compared, showing a good agreement. The complete calibration of the setup makes it a ready-to-use tool to exert local forces controlled in direction and amplitude on cells

Multiphase microfluidics enables the high-throughput manipulation of droplets for multitude of applications, from the confined fabrication of nano- and micro-objects to the parallelization of chemical reactions of biomedical or biological interest. While the standard methods to follow droplets on a chip are represented by a visual observation through either optical or fluorescence microscopy, the conjunction of microfluidic platforms with miniaturized transduction mechanisms opens new ways towards the real-time and individual tracking of each independent reactor. Here we provide an overview of the most recent droplet sensing techniques, with a special focus on those based on electrical signals for an optics-less analysis.

Life consumption monitoring is a method of quantifying the degradation of a system by monitoring the life cycle environment. With current research demonstrating the value of nanotubes as sensors, they may prove to be an inexpensive, compact, and reliable means to monitor not only system environments, but also physical signs of degradation. Life consumption monitoring of electronic assemblies can be cost-effectively done using optical strain measurement techniques. In this study, current output from an optical sensor can be used to interpret combined temperature and vibration histories. This may be accomplished by passing monofrequency light through optical fibers in a peripheral arrangement on a dummy chip. Any deviation from the null condition results in misalignment of the fibers, and hence reduction in intensity and current output. With appropriate failure data at different stress levels, it is possible to determine damage and estimate the remaining life. The key challenges are to determine whether such an optical health monitoring scheme can be sufficiently accurate and robust, and whether the results can be applied to a variety of packages at any location on a circuit assembly.

Many workers have demonstrated the potential of optical techniques to process high bandwidth data at very high computation rates.1,2 Optical processors have been proposed for such diverse applications as pattern recognition, neural networks, switching, digital computing, filtering, transformations, and matrix algebra. Since most of these methods implement specialized processors, they must be integrated into presently available digital electronic systems to obtain the necessary degree of control and flexibility for practical applications. Few systems exist today that realize the potential of these optical techniques, perhaps because of the amount of engineering and development effort that separates a successful laboratory demonstration from a useful and practical system. The engineering effort is complicated by the high bandwidth of the optical system: the input and output requirements of most optical systems can easily swamp traditional digital systems. Other complicating factors are data transduction between the electronic and optical domains, and dynamic range and signal-to-noise ratio requirements. In addition to the physical interface issues, the logical interface must be well-designed and easy to use. We present here some results of our effort to integrate a self-contained, "digital-in, digital-out" space-integrating one-dimensional matched filter system into a conventional digital processing system. This system can cross-correlate a 4000 point reference waveform with a 7000 point search waveform in about 100 µsec.

The use of optical fibers for chemical monitoring predates communications uses. In recent years, advances in fiber optic and semiconductor technology, as well as in analytical chemistry and biochemistry, have made fiber optic chemical sensors very attractive for a wide variety of environmental applications. Remote spectroscopic measurements via optical fibers (passive fiber optic chemical sensing), including fluorescence and Raman spectroscopy, and often multiplexing many fibers to provide simultaneous multipoint chemical information, have become well accepted in the process control and environmental monitoring industries. Active techniques, in which chemically sensitive devices, or “optrodes”, are attached to fibers, are being intensively studied, and a few sensor systems based on these are beginning to appear as commercial products. Intrinsic sensors, in which optical fibers are the actual chemical transduction devices, have begun to attract wide attention, because of their potential for continuous long-path monitoring. Chemical sensing requirements challenge fiber optic researchers: new optical fiber designs (D-fibers, hollow waveguides, multi-core, off-center core, tapered geometries, and others) are being investigated to enhance fiber chemical sensitivity. New fiber materials (fluorozirconate, chalcogenide, sapphire, silver halide, and others) are being developed to extend transmission into the infrared “chemical fingerprint” region of the electromagnetic spectrum.

The rod photoreceptor of the retina is a quantum detector whose physiological function in physically unfavorable conditions (body temperature, salt solution) is made possible by specific protein interactions. Photon energy is stored by the receptor protein rhodopsin (R) in a structurally transformed state. Activated R interacts with transducin (a G-protein or guanine nucleotide binding protein). This catalyses binding to G of energy-rich nucleotide which in turn releases G in an activated form. Absorption of one photon leads to the activation of 1000 G in 1 s. Analogous relay systems are found from bacteria to man. Intrinsic physical properties of the rhodopsin G-protein system allow photometric studies in situ and in real time. Activation of R and interaction with G are measurable by absorption spectrophotometry. Activation of G is measurable by light scattering (LS) changes (signals) arising from the shift of the G-protein mass during activation. A continuous transretinal, near infrared LS probing beam affords direct monitoring of G-activation induced by visual stimuli. These optical techniques, combined with biochemical and physiological approaches, have been used to study the sites of R-G interaction and the thermodynamics of the G-relay in situ. G-activation is not modulated by previous illumination, indicating a remarkable constancy of the R-G amplification step in the visual transduction pathway.

In applications of vibration energy harvesting to embedded wireless sensing, the available power and energy can be very low. This poses interesting challenges for technological feasibility if the parasitic losses in the electronics used to harvest this energy are prohibitive. In this study, we present a theory for the active control of power generation in energy harvesters in a manner which addresses and compensates for parasitic loss. We conduct the analysis in the context of a single-transducer piezoelectric bimorph cantilever beam subjected to a low-frequency impulse train. The power generation of the vibration energy harvester is maximized while considering mechanical losses, electrical losses, and the static power required to activate control intelligence and facilitate power-electronic conversion. It is shown that the optimal harvesting current can be determined through the use of linear quadratic optimal control techniques. The optimal harvesting time over which energy should be generated, following an impulse, is determined concurrently with the optimal feedback law. We show that this optimal harvesting time exhibits bifurcations as a function of the parameters characterizing the losses in the system.

Abstract The biological response of bone cells (osteoblasts and/or osteocytes) to mechanical loading is an important basic science topic in the mechanism of mechano-signal transduction in bone adaptation to mechanical loading. The characterization of this mechanism of signal transduction is crucial in the understanding of the etiology of age-related bone loss, bone loss during space flight and the optimal design of implants for total joint replacements. It has been hypothesized that deformation-generated fluid shear stress is one of the major mechanical stimuli that bone cells respond to. Many in vitro experiments utilize a parallel-plate flow chamber by imposing fluid shear stress on cultured osteoblasts. For example, changes in intracellular Ca++ levels and mitogen-activated protein kinase (MAPK) phosphorylation has been quantified in response to applied shear flow [1,2]. In these studies, the flow shear stress at the wall of the flow chamber τ wall = 6 μ Q w h 2 , where Q is the volumetric flow rate, w and h are the width and height of the flow chamber, respectively, and μ is the media viscosity. However, this wall shear stress may not indicate the actual stress state which bone cells experience, which depends on the details of the flow-cell interaction, including the mechanical properties of the cell, the attachment condition of the cell to the wall as well as the cell density. In order to obtain a quantitative relationship between the biological response of bone cells to applied shear flow, it is necessary to quantify in detail the flow-cell interaction in a typical shear flow experiment. The objective of this study was to quantify the shear stress within the cell under applied shear flow, incorporating fully coupled flow and solid deformation analyses using the finite element technique. Specifically, we examined the influence of the elastic modulus of the cell and the spacing distance between cells on the shear stress within the cell.

Aligning carbon nanotubes in any way desired is very important for many fundamental and applied research projects. In this talk, I will first discuss how to grow them with controlled diameter, length, spacing, and periodicity using catalyst prepared by magnetron sputtering, electron beam (e-beam) lithography, electrochemical deposition, and nanosphere self-assembly. Then I will present our results of field emission property of both the aligned carbon nanotubes grown on flat substrates and random carbon nanotubes grown on carbon cloth. For the aligned carbon nanotubes arrays, I will present the preliminary results of using them as photonic band gap crystals and nanoantennae. As an alternative material of carbon nanotubes, ZnO nanowires have been grown in both aligned fashion on flat substrates and random fashion on carbon cloth. Using these ZnO nanowires, good field emission properties were observed. Furthermore, I will present our recent studies on the electrical breakdown and transport properties of a single suspended nanotube grown on carbon cloth by a scanning electron microscope probe incorporated into a high resolution transmission electron microscope. As part of the potential applications, I will also discuss our recent success on molecules delivery into cells using carbon nanotubes. Finally I will talk about our most recent endeavor on achieving thermoelectric figure-of-merit (ZT) higher than 2 using our unique nanocomposite approach. Plasma-enhanced chemical vapor deposition (PECVD) was discovered by my group in 1998 to be able to grow aligned carbon nanotubes [1]. Catalyst film was first deposited by magnetron sputtering. According to the thickness of the catalytic film, aligned carbon nanotubes were grown with different diameters and spacing, and different length depending the growth time. However, the two major drawbacks are 1) that the location of where the nantoube grows can not be controlled, 2) that the spacing between the nanotubes can not be varied too much. Therefore, we immediately explored to grow aligned carbon nanotubes with the location and spacing controls using e-beam lithography [2]. Unfortunately the cost is so high that the e-beam is not suited for large scale commercialization that requires only an average site density control not the exactly location, for example, electron source. It is the cost issue that made us to develop electrochemical deposition to make catalyst dots that can be separated more than 10 micormeters between dots [3]. With such arrays, we tested many samples for field emission properties and found the optimal site density [4]. However, for applications that require the location controls, for example, photonic band gap crystals, electrochemical deposition can not be satisfactory. It is this kind of application that led us to develop the nanosphere self-assembly technique in large scale [5]. For field emission, we found that ZnO nanowires are good field emitters comparable to carbon nanotubes if they are grown with the right diameter and spacing. Here I will discuss the field emission properties of ZnO nanowires as an alternative material to carbon nanotubes [6]. Us a special kind of carbon nanotubes made by PECVD, we discovered a highly efficient molecular delivery technique, named nanotube spearing, based on the penetration of Ni-particle embedded nanotubes into cell membranes by magnetic field driving. DNA plasmids encoding the enhanced green fluorescent protein (EGFP) sequence were immobilized onto the nanotubes, and subsequently speared into targeted cells. We have achieved the unprecedented high transduction efficiency in Bal17 B-lymphoma, ex vivo B cells, and primary neurons with high viability. This technique may provide a powerful tool for high efficient gene transfer in a variety of cells, especially, the hard-to-transfect cells [7]. Conventional transport studies of multiwall carbon nanotubes (MWNTs) with only the outmost wall contacted to the electrodes via side-contact shows that a MWNT is a ballistic conductor with only the outmost wall carrying current. Here we show, by using end-contact in which every wall is contacted to the electrodes, that every wall is conducting, as evidenced by a significant amount of current drop when an innermost wall is broken at high-bias. Remarkably, the breakdown of each wall was initiated in the middle of the nanotube, not at the contacts, indicating diffusive electron transport. Using end-contact, we were able to probe the conductivity wall-by-wall and found that each wall is indeed either metallic, or semiconducting, or pseudogap-like. These findings not only reveal the intrinsic physical properties of MWNTs but also provide important guidance to MWNT-based electronic devices [8]. At the end of the talk, if time permits, I will talk about our ongoing effort on improving the figure-of-merit (ZT) of thermoelectric materials using a nanocomposite strategy to mimic the structure of the superlattice of PbTe/PbSe and Bi2Te3/Sb2Te3 hoping to reduce the thermal conductivity by a factor of 2–4 while maintaining the electrical conductivity. To make a close to 100% dense nanocomposite, we started with nanoparticles synthesis, then consolidation using both the traditional hot press and the direct current fast-heat, named plasma pressure compact, to preserve the nano size of the component particles. So far, we have seen thermal conductivity decrease by a factor of 2 in the systems of Si/Ge, PbeTe/PbSe, Bi2Te3/Sb2Te3, indicating the potential of improving ZT by a factor of 2.