Article

A Fully Integrated Wireless Flexible Ammonia Sensor Fabricated by Soft Nano-Lithography

Authors:
  • 天津大学
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Abstract

Flexible ammonia (NH3) sensors based on one-dimensional nanostructures have attracted great attention due to their high flexibility and low-power consumption. However, it is still challenging to reliably and cost-effectively fabricate ordered nanostructure-based flexible sensors. Herein, a smartphone-enabled fully integrated system based on a flexible nanowire sensor was developed for real-time NH3 monitoring. Highly aligned, sub-100 nm nanowires on a flexible substrate fabricated by facile and low-cost soft lithography were used as sensitive elements to produce impedance response. The detection signals were sent to a smartphone and displayed on the screen in real time. This nanowire-based sensor exhibited robust flexibility and mechanical durability. Moreover, the integrated NH3 sensing system presented enhanced performance with a detection limit of 100 ppb, as well as high selectivity and reproducibility. The power consumption of the flexible nanowire sensor was as low as 3 μW. By using this system, measurements were carried out to obtain reliable information about the spoilage of foods. This smartphone-enabled integrated system based on a flexible nanowire sensor provided a portable and efficient way to detect NH3 in daily life.

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... In order to achieve wearable, portable and convenient gas monitoring, wearable gas sensors have to be small in size, lightweight, lowpower consumption, and easy to integrate [61,62]. Meanwhile, wearable gas sensors are usually attached to the surface of the skin in the form of tattoo [63,64] and patch [65], or can be integrated into clothing or accessories such as wristbands [66], rings [67], clothes [68], masks [69] and gloves [70], etc. Therefore, for biosafety and compatibility with wearable technology, wearable gas sensors must have well favorable biocompatibility and mechanical deformability, so that they can conformally attach to the human body without irritation or integrated into other devices without misbehaving [71,72]. ...
... Due to the abovementioned limitations, Duan et al. [66] reported a NIL-based soft lithography technique to directly fabricate highly aligned sub-100 nm nanowires on flexible substrates (Fig. 6E). This NIL-based technique uses a hybrid soft stamp with well-defined nano-features which is fabricated by NIL on flat PDMS, allowing large area patterning of sub-100 nm nanostructures from functional material inks in one step with relatively low cost. ...
... (E) Wearable gas sensor based on parallel nanowires toward highly sensitive NH 3 detection fabricated by nanoimprinting lithography. Reproduced with permission from Ref.[66]. Copyright 2019, American Chemical Society. ...
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The past few years have witnessed the rapid innovation of wearable chemical sensors that induce impacts on various areas of our daily life. As the emerging Internet of Thing (IoT), wearable chemical sensors hold considerable promise not only for healthcare and fitness applications but also for other diversified applications ranging from environment monitoring to security/forensic identification. With the vision of more versatile, convenient, communicating and integrated, this review provides a comprehensive overview of the recent progress of wearable chemical sensors and system. First, in terms of healthcare application, the development of wearable chemical sensors for markers detection from sweat is reviewed in the aspect of transduction mechanism and structural configuration (i.e., soft/soft-hard integration patch, tattoo, and microfluidics). Then the evolution of wearable tear and saliva sensors from simple sensor design to integrated system (e.g., communication module and power supply integration) are reviewed. Next, treatment (i.e., drug delivery), as an indispensable part of close loop sensing-therapeutic system establishment, is reviewed via the representatives of microneedle technology. Additionally, the progress of wearable chemical sensors for environmental monitoring and security/forensic applications are presented, showing the development of self-sustainable/on-site testing systems. With this review, we believe the development trend of wearable chemical sensors is towards multifunctional, sensing-therapeutic, self-powered and integrated systems.
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Nanotechnology-adapted detection technologies could improve the safety and quality of foods, provide new methods to combat fraud and be useful tools in our arsenal against bioterrorism. Yet despite hundreds of published studies on nanosensors each year targeted to the food and agriculture space, there are few nanosensors on the market in this area and almost no nanotechnology-enabled methods employed by public health agencies for food analysis. This Review shows that the field is currently being held back by technical, regulatory, political, legal, economic, environmental health and safety, and ethical challenges. We explore these challenges in detail and provide suggestions about how they may be surmounted. Strategies that may have particular effectiveness include improving funding opportunities and publication venues for nanosensor validation, social science and patent landscape studies; prioritizing research and development of nanosensors that are specifically designed for rapid analysis in non-laboratory settings; and incorporating platform cost and adaptability into early design decisions. This Review presents a focused overview of nanosensor technology for ensuring the safety and quality of foods and discusses seven key challenges that are currently preventing their successful commercialization.
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Nanostructuring, including tailoring dimensionality, size and morphology, and nanopatterning, is well recognized to play an increasingly important role in sensing units/chips of electrical gas sensors. As two predominant and fundamental configurations, chemiresistor- and field emission transistor (FET)-based electrical gas sensors are receiving increasing attention for fundamental research and practical applications. Herein, state-of-the-art overviews of electrical gas sensors are presented with emphasis on the role of nanostructuring in sensing units for both chemiresistors and FETs types, the strategies for their performance enhancement, and some key sensing mechanisms involved. Nanostructuring of sensing units and their dependence of the performance of chemiresistor- and FET-based gas sensors are discussed according to zero- (0D), one-(1D), two- (2D), and three-dimension (3D), respectively. Other types of gas sensors are also mentioned briefly. Some particular strategies such as loading external heat and light sources, electrical field, and mechanical forces for providing extra freedom to improve and optimize the performance are introduced in detail. Finally, a summary and future perspectives about gas sensors are given with some novel strategies, ideas, and solutions that could make it possible to meet the requirements of rapid industrialization, informatization, intelligentization, and population expansion.
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Gaseous ammonia (NH3) under high concentration (e.g., larger than 25 ppm) is usually harmful to human organs. Instead, lower - concentration NH3 that is generated from human metabolism may serve as a biomarker for exhaled diagnosis of kidney disease. Ideally, wearable NH3 sensors integrated over cloths are highly desired for real-time monitoring. Here, twistable and tailorable nanocomposites (NCPs) textile has been developed for yielding wearable NH3 sensing, by which graphene oxide was firstly mixed with aniline monomer, and subsequently this mixture was in-situ polymerized by vanadium pentoxide to obtain a ternary NCPs of vanadium oxide, polyaniline and graphene oxide (V2O5/PANI/GO NCPs). Benefiting from the incorporation of PANI, V2O5 and GO, the V2O5/PANI/GO NCPs textile shows enhanced response (Rg/Ra -1 = 31.2±1.8% @10 ppm NH3, room temperature), high stability that maintains 91.5% response after 56 days and excellent interfering selectivity. Remarkably, the V2O5/PANI/GO NCPs textile displays excellent twistability and tailorability. This strategy to V2O5/PANI/GO NCPs textile might be extended to nanosensing materials that could be integrated onto other textiles.
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Energy harvesting is a significant issue in IoT systems. Due to the resource-constrained nature of the device and system-specific requirements for designing an IoT system, it is crucial to consider such an issue in the IoT paradigm. This chapter discusses the flexible adaption of energy harvesting issues from two significant points of view: (i) choosing appropriate fabrication methods and (ii) the need for security probation for securing data access for those sensors from placing appropriate access control solutions. Access control preserves the three commonly used security properties, namely, (i) confidentiality, (ii) integrity, and (iii) availability. Confidentiality ensures that the information remains private and will only be available to the authorized users upon request. Integrity ensures that the information is not tampered with and is being protected by others. Finally, the availability ensures that the information is available when needed. In other words, availability assures that the information is obtained by an authenticated user when required. This chapter also discusses various novel IoT architectures significant for a more efficient and effective IoT system design considering energy uses and security solutions.
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The need for flexible sensors arises from the fact their working performances are much better than their rigid counterparts. A range of flexible sensors has been developed by scientists in research labs and industries with varied fabrication techniques and processing materials. The nanomaterials and polymers used to form these sensors have enhanced electrical, mechanical and thermal characteristics. The biocompatible nature of carbon allotropes has also been popularized to devise prototypes for medical purposes. Among the fabrication techniques, the printing methods have been stressed upon due to their low cost and capability for high roll-to-roll production. These flexible differ in their physiochemical forms and operates on a specific or a combination of working mechanisms for the chosen application. This chapter explains the significance of flexible sensors by showing the techniques used to develop them, the associated raw materials and the application of these sensors. It shows the variance in some of the significant fabrication techniques used to develop the flexible sensors. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
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The excellent stretchability and biocompatibility of flexible sensors have inspired an emerging field of plant wearables, which enable intimate contact with the plants to continuously monitor the growth status and localized microclimate in real-time. Plant flexible wearables provide a promising platform for the development of plant phenotype and the construction of intelligent agriculture via monitoring and regulating the critical physiological parameters and microclimate of plants. Here, the emerging applications of plant flexible wearables together with their pros and cons from four aspects, including physiological indicators, surrounding environment, crop quality, and active control of growth, are highlighted. Self-powered energy supply systems and signal transmission mechanisms are also elucidated. Furthermore, the future opportunities and challenges of plant wearables are discussed in detail.
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Wireless chemical sensors have been developed as a result of advances in chemical sensing and wireless communication technology. Because of their mobility and widespread availability, smartphones have been extensively combined with sensors such as hand-held detectors, sensor chips, and test strips for biochemical detection. Smartphones are frequently used as controllers, analyzers, and displayers for quick, authentic, and point-of-care monitoring, which may considerably streamline the design and lower the cost of sensing systems. This study looks at the most recent wireless and smartphone-supported chemical sensors. The review is divided into four different topics that emphasize the basic types of wireless smartphone-operated chemical sensors. According to a study of 114 original research publications published during recent years, market opportunities for wireless and smartphone-supported chemical sensor systems include environmental monitoring, healthcare and medicine, food quality, sport, and fitness. The issues and illustrations for each of the primary chemical sensors relevant to many application areas are covered. In terms of performance, the advancement of technologies related to chemical sensors will result in smaller and more lightweight, cost-effective, versatile, and durable devices. Given the limitations, we suggest that wireless and smartphone-supported chemical sensor systems play a significant role in the sensor Internet of Things.
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The aim of smart and sustainable agriculture is to increase the agricultural yield at lower production price to fulfill the globally rising food demand. Although the nanofertilizers and nanopesticides are substantially contributing toward increasing the agriculture yield, the time-consuming and complex traditional methods of monitoring ammonia (NH3) emissions slow down this pace. The advanced spectroscopic monitoring techniques are efficient, but their high instrumental/operational cost, continuous human supervision, and portability issues pose limits on their applications in smart agriculture. The chemiresistive nanosensors exhibit several benefits like high sensitivity, fast real-time detection, cost-effective and labor-free operation, and stable response under changing humidity and weather conditions. This chapter explores the possibility of using chemiresistive nanosensors for agricultural NH3 monitoring. In this pursuit, several room temperature NH3 sensors based on polymers, organic materials, two-dimensional transition metal dichalcogenides, graphene, and carbon nanotubes are discussed.
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The next future strategies for improved occupational safety and health management could largely benefit from wearable and Internet of Things technologies, enabling the real-time monitoring of health-related and environmental information to the wearer, to emergency responders, and to inspectors. The aim of this study is the development of a wearable gas sensor for the detection of NH3 at room temperature based on the organic semiconductor poly(3,4-ethylenedioxythiophene) (PEDOT), electrochemically deposited iridium oxide particles, and a hydrogel film. The hydrogel composition was finely optimised to obtain self-healing properties, as well as the desired porosity, adhesion to the substrate, and stability in humidity variations. Its chemical structure and morphology were characterised by infrared spectroscopy and scanning electron microscopy, respectively, and were found to play a key role in the transduction process and in the achievement of a reversible and selective response. The sensing properties rely on a potentiometric-like mechanism that significantly differs from most of the state-of-the-art NH3 gas sensors and provides superior robustness to the final device. Thanks to the reliability of the analytical response, the simple two-terminal configuration and the low power consumption, the PEDOT:PSS/IrOx Ps/hydrogel sensor was realised on a flexible plastic foil and successfully tested in a wearable configuration with wireless connectivity to a smartphone. The wearable sensor showed stability to mechanical deformations and good analytical performances, with a sensitivity of 60 ± 8 μA decade−1 in a wide concentration range (17–7899 ppm), which includes the safety limits set by law for NH3 exposure.
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HIGHLIGHTS • The morphology of PEDOT:PSS, including in the forms of aqueous dispersions, solid films, and hydrogels, is outlined, and the application potential of PEDOT:PSS hydrogels is described. • Fabrication techniques for PEDOT:PSS-based devices are introduced, including coating, printing, conventional lithography, and soft lithography. • The latest developments in four main categories of PEDOT:PSS-based physical sensors, for humidity, temperature, pressure, and strain, respectively, are introduced. • The development prospects for PEDOT:PSS, from materials to fabrication techniques to physical sensors, are outlined.
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Achieving highly accurate responses to external stimuli during human motion is a considerable challenge for wearable devices. The present study leverages the intrinsically high surface‐to‐volume ratio as well as the mechanical robustness of nanostructures for obtaining highly‐sensitive detection of motion. To do so, highly‐aligned nanowires covering a large area were prepared by capillarity‐based mechanism. The nanowires exhibit a strain sensor with excellent gauge factor (≈35.8), capable of high responses to various subtle external stimuli (≤200 µm deformation). The wearable strain sensor exhibits also a rapid response rate (≈230 ms), mechanical stability (1000 cycles) and reproducibility, low hysteresis (<8.1%), and low power consumption (<35 µW). Moreover, it achieves a gauge factor almost five times that of microwire‐based sensors. The nanowire‐based strain sensor can be used to monitor and discriminate subtle movements of fingers, wrist, and throat swallowing accurately, enabling such movements to be integrated further into a miniaturized analyzer to create a wearable motion monitoring system for mobile healthcare. A highly sensitive flexible strain sensor that is based on large‐area of aligned nanowires is developed. The sensor can be used as a wearable device to accurately detect, discriminate and monitor subtle movements linked with human motion.
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In recent years, tremendous research interest has been triggered in the fields of flexible, wearable and miniaturized power supply devices and self-powered energy sources, in which energy harvesting/conversion devices are integrated with energy storage devices into an infinitely self-powered energy system. As opposed to conventional fabrication methods, printing techniques hold promising potency for fabrication of power supply devices with practical scalability and versatility, especially for applications in wearable and portable electronics. To further enhance the performance of the as-fabricated devices, the utilization of nanomaterials is one of the promising strategies, owing to their unique properties. In this review, an overview on the progress of printable strategies to revolutionize the fabrication of power supply devices and integrated system with attractive form factors is provided. The advantages and limitations of the commonly adopted printing techniques for power supply device fabrication are first summarized. Thereafter, the research progress on novel developed printable energy harvesting and conversion devices, including solar cells, nanogenerators and biofuel cells, and the research advances on printable energy storage devices, namely, supercapacitors and rechargeable batteries, are presented, respectively. Although exciting advances on printable material modification, innovative fabrication methods and device performance improvement have been witnessed, there are still several challenges to be addressed to realize fully printable fabrication of integrated self-powered energy sources. Open image in new window
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Highly sensitive wearable sensors that can be conformably attached to human skin or integrated with textiles to monitor the physiological parameters of human body or the surrounding environment have garnered tremendous interest. Owing to the large surface area and outstanding material properties, nanomaterials are promising building blocks for wearable sensors. Recent advances in the nanomaterial-enabled wearable sensors including temperature, electrophysiological, strain, tactile, electrochemical, and environmental sensors are presented in this review. Integration of multiple sensors for multimodal sensing and integration with other components into wearable systems are summarized. Representative applications of nanomaterial-enabled wearable sensors for healthcare, including continuous health monitoring, daily and sports activity tracking, and multifunctional electronic skin are highlighted. Finally, challenges, opportunities, and future perspectives in the field of nanomaterial-enabled wearable sensors are discussed.
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Resistive devices composed of one dimensional nanostructures are promising candidate for next generation gas sensors. However, the large-scale fabrication of nanowires is still a challenge, restricting the commercialization of such type of devices. Here, we reported a highly efficient and facile approach to fabricate poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) nanowire chemiresistive type of gas sensor by nanoscale soft lithography. Well-defined sub-100 nm nanowires are fabricated on silicon substrate which facilitates the device integration. The nanowire chemiresistive gas sensor is demonstrated for NH3 and NO2 detection at room-temperature and shows a limit of detection at ppb level which is compatible with nanoscale PEDOT:PSS gas sensors fabricated with conventional lithography technique. In comparison with PEDOT:PSS thin film gas sensor, the nanowire gas sensor exhibits a higher sensitivity and much faster response to gas molecules.
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This work details the fabrication and performance of a sensor for ammonia gas, based on conducting polymer. The fabrication procedure consists following steps; polyaniline synthesis via oxidative polymerization technique, then a sensitive polyaniline film was deposited on a printed circuit board and finally, polyaniline microdevice were assembled on an interdigitated electrode arrays to fabricate the sensor for amomonia gas detection. Response time of this chemiresistive devices and humidity impact were examined for NH3 sensitivity and compared with commercial gas sensors (Taguchi Model 826). Data export from sensor to the computer was carried out via data logger model ADC-24 and analyzed using SPSS software. The sensor was found to have a rapid (t = 40 s) and stable linear response to ammonia gas in the concentration range of interest (50–150 ppm) under room temperature operation condition. It was reviled also reliable results to the variation of environment humidity. Power consumption, sensitivity, dimension, flexibility and fabrication cost were used as most important parameters to compare the new polymer based device with those of other similar works and the results showed that small size, low cost, flexibility, low power consumption and high sensitivity are from the benefits of this innovative device. In real-time application conditions flexible polyaniline based gas sensor with polyimide substrate in thickness 0.25 mm exhibits relatively good performance and accurate evaluation of food spoilage.
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Electronics will evolve from current rigid electronics to flexible electronics to ultimate soft stretchable electronics. The currently available, rapidly evolving wearable electronics may be a transitional stage to the future stretchable electronics. One-dimensional (1D) nanomaterials are being extensively used for the design of novel wearable conductors, sensors, and energy devices because 1D nanostructures have an intrinsically high-aspect-ratio that enables the construction of conductive percolation network with small amount of material usage while maintaining high optoelectronic performance. Simultaneously, 1D nanostructures have better mechanical elasticity than corresponding bulk materials or sphere-like nanoparticles and this is a key requirement for designing electronic skin materials by circumventing material delamination and/or cracking. Here, recent progress in 1D nanomaterials based on carbon, metal, metal oxides, polymer, and their hybrid structures is reviewed, focusing on the application of soft wearable electronics. In particular, 1D nanomaterial-based stretchable conductors, wearable pressure and strain sensors, wearable energy storage devices, and stretchable light-emitting diode devices are discussed in detail. Representative fabrication methodologies are described and their advantages/disadvantages are compared. Finally, the innovative application of 1D nanomaterial-based sensors/devices in health and wellness, safety, artificial intelligence, entertainment, and early detection of mental disorders is discussed.
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Wearable sensor technologies play a significant role in realizing personalized medicine through continuously monitoring an individual’s health state. To this end, human sweat is an excellent candidate for non-invasive monitoring as it contains physiologically rich information. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate analysis of the physiological state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is critical and full system integration to ensure the accuracy of measurements is a necessity. Here, a mechanically flexible and fully-integrated perspiration analysis system is presented that simultaneously and selectively measures sweat metabolites (e.g. glucose and lactate) and electrolytes (e.g. sodium and potassium ions), as well as the skin temperature to calibrate the sensors' response. Our work bridges the technological gap between signal transduction, conditioning, processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin, and silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. The envisioned application could not have been realized by either of the technologies alone due to their respective inherent limitations. This wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor physical activities, and infer real-time assessment of the physiological state of the subjects. The platform enables a wide range of personalized diagnostic and physiological monitoring applications.
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This letter reports on the development and evaluation of a electrohydrodynamic jet printing that uses an addressable multinozzle. To reduce the interference and distortion in the electric field, a multinozzle was fabricated from a silicon wafer. The experimental conditions were optimized to prevent the jet from bending at the end of the multinozzle and to allow for independent control of each nozzle. To better evaluate this technique, simulations were performed and compared with the experimental results. We observed a strong correlation between the simulated and experimental results. In addition, each nozzle in this multinozzle could be individually controlled.
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A novel approach to improve polyaniline (PANI) electrical properties while retaining good processability was demonstrated. It has been investigated that a suitable design of the dopant counterion can improve charge transport in the amorphous phase of the polymer, thus allowing to obtain a material with good conductivity without the requirement of a high degree of crystallinity. The conductivity of PANI is enhanced by the formation of a crosslinked three-dimensional network between the polymer chains and dopant molecules. The interaction of PANI with semiconductor nanoparticles such as CdS, Cu 2S, and TiO2 has reported that the PANI chains remain in a separated phase from the inorganic compounds which do not modify the charge transport inside the polymer. The dopant promotes the formation of a cross-linked network with the PANI chains and its semiconducting nature assists the interchain charge transport.
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Large-scale integration of high-performance electronic components on mechanically flexible substrates may enable new applications in electronics, sensing and energy. Over the past several years, tremendous progress in the printing and transfer of single-crystalline, inorganic micro- and nanostructures on plastic substrates has been achieved through various process schemes. For instance, contact printing of parallel arrays of semiconductor nanowires (NWs) has been explored as a versatile route to enable fabrication of high-performance, bendable transistors and sensors. However, truly macroscale integration of ordered NW circuitry has not yet been demonstrated, with the largest-scale active systems being of the order of 1 cm(2) (refs 11,15). This limitation is in part due to assembly- and processing-related obstacles, although larger-scale integration has been demonstrated for randomly oriented NWs (ref. 16). Driven by this challenge, here we demonstrate macroscale (7×7 cm(2)) integration of parallel NW arrays as the active-matrix backplane of a flexible pressure-sensor array (18×19 pixels). The integrated sensor array effectively functions as an artificial electronic skin, capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5 V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5 mm) for over 2,000 bending cycles. This work presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.
Article
This paper reported a high-performance e-nose type chemiresistive gas sensor composed of graphene oxide (GO) doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) nanowires. Large scale and well-defined sub-100 nm nanowires were prepared using nanoscale soft lithography in a highly efficient and facile way, facilitating subsequent device integration. The responses of the nanowire sensors to volatile organic compounds (VOCs) can be tuned by the different polymer components, which are utilized to constitute unique identification codes for ethanol, n-hexane, acetone and p-xylene and realize the discrimination of different VOCs. Besides, the score plot and classification matrix obtained respectively from the principal component analysis (PCA) and linear discriminant analysis (LDA) provide sufficient information to differentiate different VOCs.
Article
Elastomeric stamps and molds provide a great opportunity to eliminate some of the disadvantages of photolithograpy, which is currently the leading technology for fabricating small structures. In the case of "soft lithography" there is no need for complex laboratory facilities and high-energy radiation. Therefore, this process is simple, inexpensive, and accessible even to molecular chemists. The current state of development in this promising area of research is presented here.
Article
We report a facile transfer method to fabricate flexible photodetectors directly on tape, wherein the films formed by different processes were integrated together. The tape-based photodetectors with CdS nanowire (NWs) active layers exhibited good performances as those fabricated by conventional processes. The obvious persistent photocurrent (PPC) in our device was eliminated by introducing a conductive polymer poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) onto the CdS NWs layer. By adjusting the concentration of the PEDOT:PSS aqueous solution, a device with a fast response, ultrashort decay time, and relatively large photocurrent was obtained. The decay times were 11.59 ms and 6.64 ms for devices using electrodes of silver NWs and gold, respectively. These values are much shorter than the shortest decay times (on the order of hundreds of milliseconds) reported previously.
Article
Nanofibers/nanowires usually exhibit exceptionally low flexural rigidities and remarkable tolerance against mechanical bending, showing superior advantages in flexible electronics applications. Electrospinning is regarded as a powerful process for this 1D nanostructure; however, it can only be able to produce chaotic fibers that are incompatible with the well-patterned microstructures in flexible electronics. Electro-hydrodynamic (EHD) direct-writing technology enables large-scale deposition of highly aligned nanofibers in an additive, noncontact, real-time adjustment, and individual control manner on rigid or flexible, planar or curved substrates, making it rather attractive in the fabrication of flexible electronics. In this Review, the ground-breaking research progress in the field of EHD direct-writing technology is summarized, including a brief chronology of EHD direct-writing techniques, basic principles and alignment strategies, and applications in flexible electronics. Finally, future prospects are suggested to advance flexible electronics based on orderly arranged EHD direct-written fibers. This technology overcomes the limitations of the resolution of fabrication and viscosity of ink of conventional inkjet printing, and represents major advances in manufacturing of flexible electronics.
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Fabrication and comparative analysis of the gas sensing devices based on individualized single-walled carbon nanotubes of four different types (pristine, boron doped, nitrogen doped and semi-conducting ones) for detection of low-concentrations of ammonia, is presented. The comparison of the detection performance of different devices, in terms of resistance change under exposure to ammonia at low concentrations combined with the detailed analysis of chemical bonding of dopant atoms to nanotube walls sheds light on the interaction of NH3 with carbon nanotubes. Furthermore, chemoresistive measurements showed that the use of semiconducting nanotubes as conducting channels leads to the highest sensitivity of devices compared to the other materials. Electrical characterization and analysis of the structure of fabricated devices showed a close relation between amount and quality of the distribution of deposited nanotubes and their sensing properties. All measurements were performed at room temperature, and the power consumption of gas sensing devices was as low as 0.6 W. Finally, the route towards an optimal fabrication of nanotube-based sensors for the reliable, energy-efficient sub-ppm ammonia detection is proposed, which matches the pave of advent of future applications.
Article
The coral-shaped Dy2O3 was prepared by a simple and environmentally friendly hydrothermal reaction combined with subsequent calcination. The coral-shaped Dy2O3 was assembled by clusters, which were constructed by nanoparticles, whose sizes are 12.3±3.6nm. The gas sensors were investigated with nine gases at room temperature, and show a high response and selectivity to NH3. Compared with other reported metal oxide-based sensors, Dy2O3 sensor exhibits not only high sensitivity, good selectivity and reproducibility to NH3 at room temperature, but also two good linear relationships when the concentration of NH3 is in the range of 0.1-1ppm and 1-100ppm. The good gas sensing property is mainly because of the 3D hierarchical structure of coral-like Dy2O3, which has a large specific surface area. This benefits NH3 molecules to adsorb/desorb onto/from the surface as well as the electron transfer. In addition, the possible NH3-sensing mechanism is discussed in detail.
Article
The aroma quality analysis in terms of sensory properties is important to the food industry. Chemical sensors based on polyaniline (PANI) films were produced and used in a sensors array (electronic nose) to distinguish three artificial aromas: strawberry, grape and apple. The sensors were produced by in situ PANI polymerization on interdigitated graphite electrodes and doped with different acids (hydrochloric acid - HCl, camphor sulfonic acid - CSA and dodecylbenzenesulfonic acid – DBSA). Morphological characterizations by field emission scanning electron microscope (FE-SEM) revealed the best superficial regularity with smaller and better distribution of particles to the HCl-doped PANI film, which exhibited highest and fastest response and best sensitivity. It was also demonstrated by principal component analysis (PCA) that the sensor array was highly efficient to distinguish artificial aromas, thereby being a promising tool for aroma quality analysis in various food industry sectors.
Article
Pristine SiO2, TiO2 and composite SiO2-TiO2 films of 200 nm thick were coated on surface of quartz acoustic wave (SAW) sensors with sol-gel and spin coating technique. Their performance and mechanisms for sensing NH3 were systematically investigated. Sensors made with the TiO2 and SiO2-TiO2 films showed positive frequency shifts, whereas SiO2 film exhibits a negative frequency shift to NH3 gas. it is believed that the negative frequency shift was mainly caused by the increase of NH3 mass loading on the sensitive film while the positive frequency shift was associated to the condensation of the hydroxyl groups (-OH) on the film making the film stiffer and lighter, when exposed to NH3 gas. It demonstrated that humidity played a significant factor on the sensing performance. Comparative studies exhibited that the sensor based on the composite SiO2-TiO2 film had a much better sensitivity to NH3 at a low concentration level (1 ppm) with a response of 2 KHz, and also showed fast response and recovery, excellent selectivity, stability and reproducibility.
Article
Flexible ammonia(NH3) sensors were fabricated on polyethylene terephthalate (PET) substrate using poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/silver nanowire (AgNW) composite film as the active layer. With AgNWs of optimized concentration being incorporated into the PEDOT:PSS film, the sensitivity of the devices was significantly improved. Even with simple digitally dispensed parallel structure electrodes, the device achieved excellent sensing performance, and was shown to be able to detect very low NH3 concentration below 500 ppb. The mechanism for the sensing performance improvement was revealed. The sensor also showed considerable selectivity with respect to water and common organic vapors. Finally, the sensor was integrated with a self-designed portable data acquisition system to monitor freshness of pork, demonstrating its feasibility for inspecting the meat quality in the early stage.
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In this work, a smartphone-enabled platform for easy and portably colorimetric analysis of 2,4,6-trinitrotoluene (TNT) using amine-trapped PDMS is designed and implemented. The amine-trapped PDMS is simply prepared by immersing the cured PDMS in aminosilane solutions forming an amine-containing polymer. After contacting with TNT-containing solutions, the colorless PDMS showed a rapid colorimetric change which can be easily identified by the naked eye. The amine-trapped PDMS was carefully optimized to achieve visible detection of TNT at concentrations as low as 1μM. Using an integrated camera in the smartphone, pictures of colored PDMS membranes can be analyzed by a home-developed mobile application. Thus, the TNT amount can be precisely quantified. Direct TNT detection in real samples (e.g. drinking, tap and lake waters) is demonstrated as well. Smartphone-enabled colorimetric method using amine-trapped PDMS membranes realizes a convenient and efficient approach towards a portable system for field TNT detections.
Article
Nanowire (NW) transfer technology has provided unprecedented strategies to realize future flexible materials and electronics. Using this technology, geometrically controlled, high-quality NW arrays can now be obtained on various flexible substrates easily with high throughput. However, it is still challenging to extend this technology to a wide range of high-performance device applications because its limited temperature tolerance precludes the use of high-temperature annealing, which is essential for NW crystallization and functionalization. A pulsed laser technique has been developed to anneal NWs in the presence of a flexible substrate; however, the induced temperature is not high enough to improve the properties of materials such as ceramics and semiconductors. Here, we present a versatile nanotransfer method that is applicable to NWs that require high-temperature annealing. To successfully anneal NWs during their transfer, the developed fabrication method involves sequential removal of a nanoscale sacrificial layer. Using this method, we first produce an ultralong, perfectly aligned polycrystalline barium titanate NW array that is heated treated at 700 °C on a flexible polyethylene terephthalate substrate. This high-quality piezoelectric NW array on a flexible substrate is used as a flexible nanogenerator that generates current and voltage 37 and 10 times higher, respectively, than those of a nanogenerator made of non-crystallized BaTiO3 nanowires.
Article
Fish is the most perishable of fresh foods, but it is held in high regard for its flavor, taste and nutrition for the human body. Until now, most studies on monitoring the freshness of fish have used semiconducting metal oxide sensors that consume much power in sensing operation. To supply the operational sensing power and the power for wireless communication, any wireless sensor module needs a battery attached, and this entails extra effort for a regular battery change. Therefore, we developed a novel fish monitoring system in which no battery is needed for the sensing module. This study proposes a novel proximal fish freshness monitoring system. The novel smart sensing tag module has been developed as a self-powered device by using an additional energy harvesting circuit that operates at a frequency of 13.56 MHz. The harvester can collect sufficient radio frequency (RF) energy from the reader by using RF energy coupling within a maximum distance of 30 cm; then, the received power is stored in a single energy chip for supplying to the sensing circuit. The fish freshness is monitored by sensor modules for temperature and either hydrogen sulfide (H2S) or ammonia (NH3) gas concentration measurement in the fish packaging. The sensing module is designed using ultra-low-power sensors that consume less than ∼10 mW, enabling us to extend the distance between the RF reader and the smart sensor tag for effective RF energy coupling and sensing data transmission. The results of freshness monitoring of a seafish package are classified into four grades to indicate the food quality: good, normal, caution, and bad. The proposed sensor tag can be used to predict the quality of packaged fish by accurate monitoring of temperature and the concentration of H2S or NH3 in range of −40 to 105 °C, 0 − 200 ppm, and 0–100 ppm, respectively.
Article
A selective room-temperature ammonia sensor using WS2 nanoflakes as the sensing materials was successfully developed in this work. The two-dimensional WS2 sharing the same structure with MoS2, has a typical graphene-like 2D microstructure. The WS2 nanoflakes based sensor shows a good sensitivity and an excellent selectivity to ammonia at room temperature. The sensor showed an increased resistance when exposed to ammonia from 1 ppm to 10 ppm indicating a p-type response. The response and recovery time of the sensor to 5 ppm ammonia are ∼120 s and ∼150 s, respectively. The developed ammonia sensor shows excellent selectivity to formaldehyde, ethanol, benzene and acetone at room temperature. The response of the sensor increased as the humidity increase up to 73% possibly due to the sulfides ions-assisted hydroxylation of the co-adsorbed water and the oxidation of the solvated ammonia with adsorbed oxygen ions on the surface of the WS2 nanoflakes.
Article
Pt-loaded mesoporous WO3 was fabricated by nanocasting method. Mesoporous structure provided ordered tunnel which was convenient for gas diffusion and the large specific surface area which could offer more active sites. The noble metal (Pt) improved the catalytic efficiency which played crucial role in enhancing the performance of the gas sensor. The obtained materials were characterized by X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Characterization indicated that the synthesized materials had ordered mesoporous structure with excellent crystallinity and the pore size was about 10.6 nm. Static test system was employed to measure ammonia sensing properties for the as-prepared samples. The sensor based on Pt-loaded WO3 presented higher sensitivity, quicker response-recovery rates, excellent repeatability and selectivity. It indicated that the Pt-loaded mesoporous WO3 was a potential ammonia gas sensor material.
Article
Homeostasis of ionized calcium in biofluids is critical for human biological functions and organ systems. Measurement of ionized calcium for clinical applications is not easily accessible due to its strict procedures and dependence on pH. pH balance in body fluids greatly affects metabolic reactions and biological transport systems. Here, we demonstrate a wearable electrochemical device for continuous monitoring of ionized calcium and pH of body fluids using a disposable and flexible array of Ca2+ and pH sensors that interfaces with a flexible printed circuit board (FPCB). This platform enables real-time quantitative analysis of these sensing elements in body fluids such as sweat, urine, and tears. Accuracy of Ca2+ concentration and pH measured by the wearable sensors are validated through Inductively Couple Plasma - Mass Spectrometry (ICP-MS) technique and a commercial pH meter respectively. Our results show that the wearable sensors have high repeatability and selectivity to the target ions. Real-time on-body assessment of sweat is also performed, and our results indicate that calcium concentration increases with decreasing pH. This platform can be used in non-invasive continuous analysis of ionized calcium and pH in body fluids for disease diagnosis such as primary hyperparathyroidism and kidney-stone.
Article
A hierarchically nanostructured graphene-polyaniline composite film is developed and assembled for a flexible, transparent electronic gas sensor to be integrated into wearable and foldable electronic devices. The hierarchical nanocomposite film is obtained via aniline polymerization in reduced graphene oxide (rGO) solution and simultaneous deposition on flexible PET substrate. The PANI nanoparticles (PPANI) anchored onto rGO surfaces (PPANI/rGO) and the PANI nanofiber (FPANI) are successfully interconnected and deposited onto flexible PET substrates to form hierarchical nanocomposite (PPANI/rGO-FPANI) network films. The assembled flexible, transparent electronic gas sensor exhibits high sensing performance towards NH3 gas concentrations ranging from 100 ppb to 100 ppm, reliable transparency (90.3% at 550 nm) for the PPANI/rGO-FPANI film (6 h sample), fast response/recovery time (36 s/18 s), and robust flexibility without an obvious performance decrease after 1000 bending/extending cycles. The excellent sensing performance could probably be ascribed to the synergetic effects and the relatively high surface area (47.896 m(2) g(-1)) of the PPANI/rGO-FPANI network films, the efficient artificial neural network sensing channels, and the effectively exposed active surfaces. It is expected to hold great promise for developing flexible, cost-effective, and highly sensitive electronic sensors with real-time analysis to be potentially integrated into wearable flexible electronics.
Article
A flexible and wearable microsensor array is described for simultaneous multiplexed monitoring of heavy metals in human body fluids. Zn, Cd, Pb, Cu, and Hg ions are chosen as target analytes for detection via electrochemical square wave anodic stripping voltammetry (SWASV) on Au and Bi microelectrodes. The oxidation peaks of these metals are calibrated and compensated by incorporating a skin temperature sensor. High selectivity, repeatability, and flexibility of the sensor arrays are presented. Human sweat and urine samples are collected for heavy metal analysis, and measured results from the microsensors are validated through inductively coupled plasma mass spectrometry (ICP-MS). Real-time on-body evaluation of heavy metal (e.g. zinc and copper) levels in sweat of human subjects by cycling is performed to examine the change in concentrations with time. This platform is anticipated to provide insightful information about an individual’s health state such as heavy metal exposure and aid the related clinical investigations.
Article
A flexible humidity sensor has been fabricated by a transfer printing technique. The device is fabricated by spin coating a composite of an equal (1:1) wt% ink of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and zinc-stannate (ZnSnO3) on a water soluble substrate (WSS), screen printing silver interdigitated (IDT) electrodes and spin coating low modulus Polydimethylsiloxane (PDMS) on top of the IDTs. The water soluble substrate is then dissolved and removed and the device is laminated onto an arbitrary substrate in an inverted configuration. The device performance has been tested by transferring onto curved plastic substrates with different radii of curvature Rc. The devices show impedance change from ∼18MΩ to ∼1.8MΩ from 0% to 90% relative humidity (RH) with a negligible variation in results, over different bending radii. The transfer printing technique reported here would provide efficient and reliable route for the fabrication of flexible electronics on nonconventional substrates in environmental sensing, soft robotics, and artificial skin etc.
Article
The TiO2@WO3 core–shell composite with mass ratio of core and shell4:1 was prepared by a hydrothermal synthesis method using sodium tungstate dehydrate, nitric acid and commercial TiO2 powder as raw materials. A novel mixed potential NH3 sensor was fabricated by using above-mentioned TiO2@WO3 as sensing electrode and La10Si5.5Al0.5O27 as solid electrolyte. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and structure of the samples. The sensor response to NH3 was examined at 400 ∼ 550 °C. The experimental results indicated that the sensor based on TiO2@WO3 sensing electrode possessed greatly enhanced NH3 sensing properties including higher and more stable response value and faster response rate compared to the sensor using TiO2, WO3 or TiO2-WO3 mixture sensing electrode under the same conditions. The responding potential values of the sensor with TiO2@WO3 sensing electrode exhibited a linear dependence on the logarithm of the NH3 concentrations. The highest NH3 sensitivity of 74.8 mV/decade was achieved at 450 °C. In the meantime, the sensors also showed well anti-interference capability to CH4, CO2 and H2, but noticeable cross sensitivity toward NO2 was observed. O2 effect on responding signal could be calibrated by predetermining O2 content.
Article
The successful application of focused electron (and ion) beam induced deposition techniques for the growth of nanowires on flexible and transparent polycarbonate films is reported here. After minimization of charging effects in the substrate, sub-100 nm-wide Pt, W and Co nanowires have been grown and their electrical conduction is similar compared to the use of standard Si-based substrates. Experiments where the substrate is bent in a controlled way indicate that the electrical conduction is stable up to high bending angles, >50º, for low-resistivity Pt nanowires grown by the ion beam. On the other hand, the resistance of Pt nanowires grown by the electron beam changes significantly and reversibly with the bending angle. Aided by the substrate transparency, a diffraction grating in transmission mode has been built based on the growth of an array of Pt nanowires that shows sharp diffraction spots. The set of results supports the large potential of focused beam deposition as a high-resolution nanolithography technique on transparent and flexible substrates. The most promising applications are expected in flexible nano-optics and nano-plasmonics, flexible electronics and nano-sensing.
Article
The development of printed electronics will require the ability to deposit a wide range of nano-materials using printing techniques. Here we demonstrate the controlled deposition of networks of silver nanowires in well-defined patterns by inkjet printing from an optimized isopropanol-diethylene glycol dispersion. We find that great care must be taken while producing the ink and during solvent evaporation. The resultant networks have good electrical properties, displaying sheet resistances as low as 8 Ohn/sq and conductivities as high as 105 S/m. Such optimised performances was achieved for line widths of 1-10 mm, and network thicknesses of 0.5-2 um deposited from ~10-20 passes while using processing temperatures of no more than 110 oC. Thin networks are semi-transparent with DC to optical conductivities of ~40.
Article
The motivation of this research is to develop a smart NH3 sensor based on rGO-PANI hybrid loading on flexible PET thin film by in situ chemical oxidative polymerization. The sensor not only exhibits high sensitivity, good selectivity and fast response under room temperature but also has flexibility, cheap and wearable characteristics.
Article
This work presents a simple, low-cost and practical inkjet-printing technique for fabricating an innovative flexible gas sensor made of graphene-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite film with high uniformity over a large area. An electronic ink prepared by graphene dispersion in PEDOT:PSS conducting polymer solution is inkjet-printed on a transparency substrate with prefabricated electrodes and investigated for ammonia (NH3) detection at room temperature. Transmission electron microscopy, Fourier transform infrared spectroscopy, UV-visible spectrometer and Raman characterizations confirm the presence of few-layer graphene in PEDOT:PSS polymer matrix and the present of pi-pi interactions between graphene and PEDOT:PSS. The ink-jet printed graphene-PEDOT:PSS gas sensor exhibits high response and high selectivity to NH3 in a low concentration range of 25-1000 ppm at room temperature. The attained gas-sensing performance may be attributed to the increased specific surface area by graphene and enhanced interactions between the sensing film and NH3 molecules via pi electrons network. The NH3-sensing mechanisms of the flexible printed gas sensor based on chemisorbed oxygen interactions, direct charge transfers and swelling process are highlighted.
Article
The manuscript reports a novel and simple fabrication of paper-based flexible ammonia gas (NH3) sensor with silver and poly(m-aminobenzene sulfonic acid) functionalized single-walled carbon nanotubes (SWNT-PABS) via inkjet printing. Silver dispersion was first inkjet printed onto the photo-paper to prepare the electrodes with different configurations. SWNT-PABS dispersion was then printed onto pre-printed silver electrodes to fabricate the ammonia gas sensor. The rheological behaviors of SWNT-PABS dispersion and surface structures of fabricated sensors were characterized. The effects of electrode configuration and the number of SWNT-PABS printed layers on the electric resistance of sensors were studied. The paper-based sensor showed excellent sensor response, short response and recovery time to different concentrations of NH3 at ppm level, and could be stable for several months. This fabrication method assembling electrodes and testing parts onto the flexible photo-paper is simpler, more efficient, and cost effective.
Article
We present the fabrication and characterization of new type of flexible gas sensors, composed mainly of a bottom ZnO conductive layer on metal foil, vertically aligned ZnO nanorod channel, and graphene-based top conductive electrode. Multiple cycling tests demonstrated the ZnO nanorods (NRs) and graphene (Gr) hybrid architectures accommodated the flexural deformation without mechanical or electrical failure for bending radius below 0.8cm under the repeated bending and releasing up to 100 times. In addition, the hybrid architectures fabricated on glass substrate showed good optical transmittance larger than ∼70% for visible light, indicating potential application in transparent devices. Furthermore, our gas sensors demonstrated the ppm level detection of ethanol gas vapor with the sensitivity (resistance in air/resistance in target gas) as high as ∼9 for 10ppm ethanol.
Article
Owing to their promising applications in electronic and optoelectronic devices, conducting polymers have been continuously studied during the past few decades. Nevertheless, only limited progress had been made in conducting-polymer-based sensors until nanostructured conducting polymers were demonstrated for high-performance signal transducers. Significant advances in the synthesis of conducting-polymer nanomaterials have been recently reported, with enhanced sensitivity relative to their bulk counterparts. Today, conducting-polymer nanomaterials rival metal and inorganic semiconductor nanomaterials in sensing capability. However, there are still several technological challenges to be solved for practical sensor applications of conducting-polymer nanomaterials. Here, the key issues on conducting-polymer nanomaterials in the development of state-of-the-art sensors are discussed. Furthermore, a perspective on next-generation sensor technology from a materials point of view is also given.
Article
This paper describes materials and mechanics aspects of bending in systems consisting of ribbons and bars of single crystalline silicon supported by sheets of plastic. The combined experimental and theoretical results provide an understanding for the essential behaviors and for mechanisms associated with layouts that achieve maximum bendability. Examples of highly bendable silicon devices on plastic illustrate some of these concepts. Although the studies presented here focus on ribbons and bars of silicon, the same basic considerations apply to other implementations of inorganic materials on plastic substrates, ranging from amorphous or polycrystalline thin films, to collections of nanowires and nanoparticles. The contents are, as a result, relevant to the growing community of researchers interested in the use of inorganic materials in flexible electronics.
Article
Electrically conductive polymer blends containing polyaniline doped with dodecyl benzene sulfonic acid (PANI-DBSA) dispersed in a polystyrene (PS) matrix were studied as sensing materials for an homologous series of alcohols, including, methanol, ethanol and 1-propanol. The blends were prepared by melt processing of PS/PANI-DBSA powders (prepared by blending of dispersions of PANI-DBSA and PS followed by coagulation) characterized by high conductivities at relatively low PANI-DBSA concentrations. Extruded PS/PANI-DBSA filaments produced by a capillary rheometer process at various shear rate levels were used in the sensing experiments. A significant conductivity increase was observed upon exposure of the filaments to the various alcohols. Some systems have demonstrated high sensitivity (relative resistance changes of few orders of magnitude) towards the studied alcohols combined with outstanding reproducibility and recovery behavior. The sensing performance and mechanism of these filaments are governed by the dopant content and method of processing. Under certain processing conditions a unique PANI network containing nanosized particles is realized, resulting in very high sensitivity levels. It is suggested that the observed resistance changes of these PS/PANI filaments result from enhanced charge carrier mobility through hopping processes between adjacent PANI particles.
Article
We report here a simple and effective approach, named scalable sweeping-printing-method, for fabricating flexible high-output nanogenerator (HONG) that can effectively harvesting mechanical energy for driving a small commercial electronic component. The technique consists of two main steps. In the first step, the vertically aligned ZnO nanowires (NWs) are transferred to a receiving substrate to form horizontally aligned arrays. Then, parallel stripe type of electrodes are deposited to connect all of the NWs together. Using a single layer of HONG structure, an open-circuit voltage of up to 2.03 V and a peak output power density of approximately 11 mW/cm(3) have been achieved. The generated electric energy was effectively stored by utilizing capacitors, and it was successfully used to light up a commercial light-emitting diode (LED), which is a landmark progress toward building self-powered devices by harvesting energy from the environment. This research opens up the path for practical applications of nanowire-based piezoelectric nanogeneragtors for self-powered nanosystems.
Article
The task of nanofabrication can, in principle, be divided into two separate tracks: generation and replication of the patterned features. These two tracks are different in terms of characteristics, requirements, and aspects of emphasis. In general, generation of patterns is commonly achieved in a serial fashion using techniques that are typically slow, making this process only practical for making a small number of copies. Only when combined with a rapid duplication technique will fabrication at high-throughput and low-cost become feasible. Nanoskiving is unique in that it can be used for both generation and duplication of patterned nanostructures.