211 research outputs found

    Using ultra-thin parylene films as an organic gate insulator in nanowire field-effect transistors

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    We report the development of nanowire field-effect transistors featuring an ultra-thin parylene film as a polymer gate insulator. The room temperature, gas-phase deposition of parylene is an attractive alternative to oxide insulators prepared at high temperatures using atomic layer deposition. We discuss our custom-built parylene deposition system, which is designed for reliable and controlled deposition of <100 nm thick parylene films on III-V nanowires standing vertically on a growth substrate or horizontally on a device substrate. The former case gives conformally-coated nanowires, which we used to produce functional Ω\Omega-gate and gate-all-around structures. These give sub-threshold swings as low as 140 mV/dec and on/off ratios exceeding 10310^3 at room temperature. For the gate-all-around structure, we developed a novel fabrication strategy that overcomes some of the limitations with previous lateral wrap-gate nanowire transistors. Finally, we show that parylene can be deposited over chemically-treated nanowire surfaces; a feature generally not possible with oxides produced by atomic layer deposition due to the surface `self-cleaning' effect. Our results highlight the potential for parylene as an alternative ultra-thin insulator in nanoscale electronic devices more broadly, with potential applications extending into nanobioelectronics due to parylene's well-established biocompatible properties

    Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

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    Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met

    Acoustic Wave Biosensors for Biomechanical and Biological Characterization of Cells

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    During past decades, interest in development of cell-based biosensors has increased considerably. In this study, two kinds of acoustic wave sensors are adopted as the cell-based biosensors to investigate the biomechanical and biological behaviors of cells, the quartz thickness shear mode (TSM) resonator and Love wave sensor. For the first part, the quartz TSM resonator is applied to detect the structural and mechanical properties of tendon stem/progenitor cells (TSCs), which are one kind of newly discovered adult cells in tendons, and the platelets from blood. Through the TSM resonator, the related viscoelastic properties of cells are extracted, which could indicate the state of cells in different physiological conditions. The TSM resonator sensor is utilized to characterize the aging-related viscoelasticity differences between the aging and young TSCs, and also to monitor the dynamic activation process of platelets. For the second part, a 36˚ YX-LiTaO3 Love wave sensor with a parylene-C wave guiding layer is proposed as a cell-based biosensor. A theoretical model is derived, to describe the Love wave propagation in the wave guiding layer, the adherent cell layer, and penetration into the liquid medium. The Love wave sensor is used to monitor the adhesion process of cells. Compared with TSM resonator, the response of Love wave sensor to the cell adhesion is primarily induced by the formation of bonds between cells and the substrate. The numerical results indicate that the adherent cell layer of various storage or loss shear modulus in certain range can cause evident, characteristic variations in propagation velocity and propagation loss, revealing the potential of Love wave sensors in providing useful quantitative measures on cellular mechanical properties. In addition, a Love wave sensor with a phononic wave guiding layer is introduced for non-operation signal filtering and sensor sensitivity improvement. Both two kinds of acoustic wave sensors present their own advantages as the cell-based biosensors, indicating advisable techniques for investigating cell biology in general and certain physiological processes in particular

    Surface Acoustic Wave (SAW) Resonators for Monitoring Conditioning Film Formation

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    We propose surface acoustic wave (SAW) resonators as a complementary tool for conditioning film monitoring. Conditioning films are formed by adsorption of inorganic and organic substances on a substrate the moment this substrate comes into contact with a liquid phase. In the case of implant insertion, for instance, initial protein adsorption is required to start wound healing, but it will also trigger immune reactions leading to inflammatory responses. The control of the initial protein adsorption would allow to promote the healing process and to suppress adverse immune reactions. Methods to investigate these adsorption processes are available, but it remains difficult to translate measurement results into actual protein binding events. Biosensor transducers allow user-friendly investigation of protein adsorption on different surfaces. The combination of several transduction principles leads to complementary results, allowing a more comprehensive characterization of the adsorbing layer. We introduce SAW resonators as a novel complementary tool for time-resolved conditioning film monitoring. SAW resonators were coated with polymers. The adsorption of the plasma proteins human serum albumin (HSA) and fibrinogen onto the polymer-coated surfaces were monitored. Frequency results were compared with quartz crystal microbalance (QCM) sensor measurements, which confirmed the suitability of the SAW resonators for this application

    Polymer Coated Rayleigh SAW and STW Resonators for Gas Sensor Applications

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    Ion-beam technology and applications

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    Ion propulsion research and development yields a mature technology that is transferable to a wide range of nonpropulsive applications, including terrestrial and space manufacturing. A xenon ion source was used for an investigation into potential ion-beam applications. The results of cathode tests and discharge-chamber experiments are presented. A series of experiments encompassing a wide range of potential applications is discussed. Two types of processes, sputter deposition, and erosion were studied. Some of the potential applications are thin-film Teflon capacitor fabrication, lubrication applications, ion-beam cleaning and polishing, and surface texturing

    Sensors and Biosensors for C-Reactive Protein, Temperature and pH, and Their Applications for Monitoring Wound Healing: A Review

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    Wound assessment is usually performed in hospitals or specialized labs. However, since patients spend most of their time at home, a remote real time wound monitoring would help providing a better care and improving the healing rate. This review describes the advances in sensors and biosensors for monitoring the concentration of C-reactive protein (CRP), temperature and pH in wounds. These three parameters can be used as qualitative biomarkers to assess the wound status and the effectiveness of therapy. CRP biosensors can be classified in: (a) field effect transistors, (b) optical immunosensors based on surface plasmon resonance, total internal reflection, fluorescence and chemiluminescence, (c) electrochemical sensors based on potentiometry, amperometry, and electrochemical impedance, and (d) piezoresistive sensors, such as quartz crystal microbalances and microcantilevers. The last section reports the most recent developments for wearable non-invasive temperature and pH sensors suitable for wound monitoring

    Surface Generated Acoustic Wave Biosensors for the Detection of Pathogens: A Review

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    This review presents a deep insight into the Surface Generated Acoustic Wave (SGAW) technology for biosensing applications, based on more than 40 years of technological and scientific developments. In the last 20 years, SGAWs have been attracting the attention of the biochemical scientific community, due to the fact that some of these devices - Shear Horizontal Surface Acoustic Wave (SH-SAW), Surface Transverse Wave (STW), Love Wave (LW), Flexural Plate Wave (FPW), Shear Horizontal Acoustic Plate Mode (SH-APM) and Layered Guided Acoustic Plate Mode (LG-APM) - have demonstrated a high sensitivity in the detection of biorelevant molecules in liquid media. In addition, complementary efforts to improve the sensing films have been done during these years. All these developments have been made with the aim of achieving, in a future, a highly sensitive, low cost, small size, multi-channel, portable, reliable and commercially established SGAW biosensor. A setup with these features could significantly contribute to future developments in the health, food and environmental industries. The second purpose of this work is to describe the state-of-the-art of SGAW biosensors for the detection of pathogens, being this topic an issue of extremely importance for the human health. Finally, the review discuses the commercial availability, trends and future challenges of the SGAW biosensors for such applications

    Approaches to Studying Bacterial Biofilms in the Bioeconomy with Nanofabrication Techniques and Engineered Platforms.

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    Studies that estimate more than 90% of bacteria subsist in a biofilm state to survive environmental stressors. These biofilms persist on man-made and natural surfaces, and examples of the rich biofilm diversity extends from the roots of bioenergy crops to electroactive biofilms in bioelectrochemical reactors. Efforts to optimize microbial systems in the bioeconomy will benefit from an improved fundamental understanding of bacterial biofilms. An understanding of these microbial systems shows promise to increase crop yields with precision agriculture (e.g. biosynthetic fertilizer, microbial pesticides, and soil remediation) and increase commodity production yields in bioreactors. Yet conventional laboratory methods investigate these micron-scale biofilms with macro-scale vessels and are limited in experimental throughput. This dissertation leverages nanofabrication techniques to engineer novel platforms for the study of bacterial biofilms from the bioeconomy. Nanofabrication can create micron-scale environments for bacterial biofilm studies and gain measurements inaccessible to conventional laboratory methods. Nanofabrication techniques can control physical and chemical influences (e.g. fluid flow, topography, confinement, surface roughness, chemistry, etc.) to mimic features of the natural environment. Platform design can also be aligned with microscopy and custom image processing algorithms to amass large datasets. Silane functionalization, together with image processing, investigated Pantoea YR343 biofilm propagation and enumerated the honeycomb biofilm morphology

    Toward a new generation of photonic humidity sensors

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    This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors
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