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A Fully Integrated Wireless Flexible Ammonia Sensor Fabricated by Soft Nano-Lithography
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.
... Nano-imprinting lithography defines a group of soft lithography methods, which requires a rigid stamp, and a polymer layer applied to a substrate. The particular protocol depends on the type of NIL method which are distinguished as thermal NIL, UV NIL, two-photon nanolithography [184,185], laser-assisted direct imprint (LADI) [186,187], nano-electrode lithography, and soft nanolithography [188]. In the case of the thermal NIL, the polymer layer and a stamp are heated above the glass transition temperature, then the stamp is evenly pressed against the polymer layer to be further used for printing. ...
... This group of methods is favored to design LEDs [189] and gas sensors [188]. In particular, it was used to fabricate a low-power consumption ammonia sensor [188] as shown in Figure 13. ...
... This group of methods is favored to design LEDs [189] and gas sensors [188]. In particular, it was used to fabricate a low-power consumption ammonia sensor [188] as shown in Figure 13. Densely ordered and oriented NWs based on PEDOT:PSS, ZnO, GO, and In(NO3)3 up to 100 nm thick, were deposited on the surface of a flexible PET substrate. ...
Herein, we review printing technologies which are commonly approbated at recent time in the course of fabricating gas sensors and multisensor arrays, mainly of chemiresistive type. The most important characteristics of the receptor materials, which need to be addressed in order to achieve a high efficiency of chemisensor devices, are considered. The printing technologies are comparatively analyzed with regard to, (i) the rheological properties of the employed inks representing both reagent solutions or organometallic precursors and disperse systems, (ii) the printing speed and resolution, and (iii) the thickness of the formed coatings to highlight benefits and drawbacks of the methods. Particular attention is given to protocols suitable for manufacturing single miniature devices with unique characteristics under a large-scale production of gas sensors where the receptor materials could be rather quickly tuned to modify their geometry and morphology. We address the most convenient approaches to the rapid printing single-crystal multisensor arrays at lab-on-chip paradigm with sufficiently high resolution, employing receptor layers with various chemical composition which could replace in nearest future the single-sensor units for advancing a selectivity.
... 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. ...
With the progress of intelligent and digital healthcare, wearable sensors are attracting considerable attention due to their portable and real-time monitoring capabilities. Among them, wearable gas sensors, which can detect both gas markers from the human body and hazardous gas from the environment, are particularly gaining tremendous interest. To ensure the gas sensors can be worn and carried easily, most of them were fabricated on flexible substrates. However, some traditional fabrication techniques of gas sensors such as lithography and chemical vapor deposited, are incompatible with most flexible substrates due to the flexible substrates cannot endure the harsh fabricated conditions, for instance, high temperature. Therefore, fabrication techniques for wearable gas sensors are extremely limited, thus a summary of which is necessary. Here, recent advances in the fabrication techniques of wearable gas sensors are presented. Fabrication techniques included coating techniques, printing techniques, spinning techniques, and transferring techniques are discussed in detail, respectively.
... Electrochemical sensors are used to analyse gases that possess active electrochemical properties which also experience inherent drawbacks such as electrode poisoning meanwhile the performance of optical sensors were limited due to their poor stability, high cost and compatibility [6]. Relative to other sensor technologies, chemiresistive gas sensors outruns the most others due to its cost effectiveness, high precision, portability and its ability to be integrated into wearable and mobile gadgets [7]. Recently, intense efforts have been dedicated for the fabrication of Transition Metal Dichalcogenides (TMDC) based chemiresistive ammonia gas sensors among which Molybdenum Disulphide (MoS 2 ) has been investigated as the most promising gas sensor due to its layer dependent properties [8], tuneable bandgap [9], high abundance, excellent stability [10], surplus active sites [11] and biocompatibility [12]. ...
... In our work, when the Z5 sensor was subjected to NH 3 vapor, the preabsorbed oxygen species on the surface of Z5 reduces NH 3 gas molecules into NO and H 2 O according to equation (7). Consequently, an electron gets transferred from the ammonia gas molecule to the conduction band of Zn doped MoS 2 /RGO that in turn curtails the hole concentration of the corresponding sensor. ...
Zinc (Zn) doping induced synergetic effects of defects engineering and heterojunction in Molybdenum disulphide/Reduced graphene oxide (MoS2/RGO) effectively enhances the p-type Volatile organic compounds (VOC) gas sensing traits and helps in tailoring the over dependence on noble metals for surface sensitization. Through this work, we have successfully prepared Zn doped MoS2 grafted on RGO employing an in-situ hydrothermal method. Optimal doping concentration of Zn dopants in the MoS2 lattice triggered more active sites on the basal plane of MoS2 with the aid of defects promoted by the zinc dopants. Effective intercalation of RGO further boost up the exposed surface area of Zn doped MoS2 for further interaction of ammonia gas molecules. Besides, smaller crystallite size brought out by 5% Zn dopants aids in efficient charge transfer across the heterojunctions that further amplifies the ammonia sensing traits with a peak response of 32.40% along with a response time of 21.3 s and recovery time of 44.90 s. The as prepared ammonia gas sensor exhibited excellent selectivity and repeatability. The obtained results reveal that transition metal doping into the host lattice proves to be a promising approach for VOC sensing characteristics of p-type gas sensors and gives insight about the importance of dopants and defects for the development of highly efficient gas sensors in the future.
... Ma et al. developed a high-performance nanostructured conductive polymer as a switch material for NFC tags to enable the detection of NH 3 [18]. Overall, current research efforts primarily concentrate on innovations in application [19,20], the preparation process of sensor and substrate materials [21], and synthesis of gas sensing materials [22,23]. The structure of LC gas sensors is relatively homogeneous, i.e., gas sensing materials are coated on the interdigital capacitors (IDC) directly, or coated after adding a dielectric layer. ...
This work presents an LC resonant passive wireless gas sensor with a novel structure designed to mitigate the negative impact of substrate. The LC sensor antenna in the new structure, and the reader antenna, were designed and optimized utilizing HFSS software to improve the transfer efficiency. The superiority of the designed structure compared with general examples is highlighted and verified. The change in the substrate capacitance essentially makes no interference with the parameters of the LC sensor to be measured. The sensor for the new structure was prepared by combining etching and sputtering methods. The ZnO nanowires (NWs) were characterized to confirm their high purity and wurtzite crystal structure. The LC gas sensors demonstrated excellent wireless sensing performance, including a low detection limit of 0.5 ppm NO2, high response of 1.051 and outstanding stability at 180 °C. The newly developed sensor structure not only prevented interference from the substrate during gas sensing testing, but also expanded the choice of sensor substrates, playing a critical role in the development of sensors based on the LC resonance principle.
... Ma et al. developed a high-performance nanostructured conductive polymer as a switch material of NFC tags to enable the detection of NH3 [18]. Overall, current research efforts primarily concentrate on the innovation of application [19,20], the preparation process of sensor and substrate materials [21], and synthesis of gas sensing materials [22,23]. The structure of LC gas sensors is relatively homogeneous, namely gas sensing materials being coated on the interdigital capacitors (IDC) directly or coated after adding a dielectric layer. ...
This work presents an LC resonant passive wireless gas sensor with a novel structure designed to mitigate the negative impact of substrate. The LC sensor antenna with the new structure and the reader antenna were designed and optimized utilizing HFSS software to improve the transfer efficiency. The superiority of the designed structure compared with the general ones is highlighted and verified. The change in the substrate capacitance has essentially no interference with the parameters to be measured of the LC sensor. The sensor with the new structure was prepared by combining etching and sputtering methods. The structure of the ZnO nanowires (NWs) was characterized to confirm their high purity and wurtzite crystal structure. The LC gas sensors demonstrated excellent wireless sensing performance including a low detection limit of 0.5 ppm NO2, high response of 1.058 and outstanding stability at 180 °C. The developed new sensor structure not only prevented interference from the substrate during gas sensing testing, but also expanded the choice of sensor substrates, playing a critical role in the development of sensors based on LC resonance principle.
... Each of these methods has advantages and disadvantages. Fluorescence is a method with very high sensitivity and is used in a wide range (Tang et al., 2019;Xiao et al., 2020;Kearns et al., 2017). The colorimetric method is similar to fluorescence but has a lower sensitivity. ...
Nanosensors work on the "Nano" scale. "Nano" is a unit of measurement around 10 − 9 m. A nanosensor is a device capable of carrying data and information about the behavior and characteristics of particles at the nanoscale level to the macroscopic level. Nanosensors can be used to detect chemical or mechanical information such as the presence of chemical species and nanoparticles or monitor physical parameters such as temperature on the nanoscale. Nanosensors are emerging as promising tools for applications in agriculture. They offer an enormous upgrade in selectivity, speed, and sensitivity compared to traditional chemical and biological methods. Nanosensors can be used for the determination of microbe and contaminants. With the advancement of science in the world and the advent of electronic equipment and the great changes that have taken place in recent decades, the need to build more accurate, smaller and more capable sensors was felt. Today, high-sensitivity sensors are used that are sensitive to small amounts of gas, heat, or radiation. Increasing the sensitivity, efficiency and accuracy of these sensors requires the discovery of new materials and tools. Nano sensors are nanometer-sized sensors that, due to their small size and nanometer size, have such high accuracy and responsiveness that they react even to the presence of several atoms of a gas. Nano sensors are inherently smaller and more sensitive than other sensors. Resumo Os nanossensores funcionam na escala "Nano". "Nano" é uma unidade de medida em torno de 10-9 m. Um nanosensor é um dispositivo capaz de transportar dados e informações sobre o comportamento e as características das partículas no nível da nanoescala para o nível macroscópico. Os nanossensores podem ser usados para detectar informações químicas ou mecânicas, como a presença de espécies químicas e nanopartículas, ou monitorar parâmetros físicos, como temperatura em nanoescala. Os nanossensores estão surgindo como ferramentas promissoras para aplicações na agricultura. Eles oferecem uma abrangente atualização em seletividade, velocidade e sensibilidade em comparação com os métodos químicos e biológicos tradicionais. Os nanossensores podem ser usados para a determinação de micróbios e contaminantes. Com o avanço da ciência no mundo e o advento dos equipamentos eletrônicos e as grandes mudanças ocorridas nas últimas décadas, sentiu-se a necessidade de construir sensores mais precisos, menores e mais capazes. Hoje, são usados sensores de alta sensibilidade que são sensíveis a pequenas quantidades de gás, calor ou radiação. Aumentar a sensibilidade, eficiência e precisão desses sensores requer a descoberta de novos materiais e ferramentas. Os nanossensores são sensores de tamanho nanométrico que, devido ao seu tamanho pequeno e tamanho nanométrico, possuem uma precisão e capacidade de resposta tão altas que reagem até mesmo na presença de vários átomos de um gás. Os nanossensores são inerentemente menores e mais sensíveis do que outros sensores.
... Each of these methods has advantages and disadvantages. Fluorescence is a method with very high sensitivity and is used in a wide range (Tang et al., 2019;Xiao et al., 2020;Kearns et al., 2017). The colorimetric method is similar to fluorescence but has a lower sensitivity. ...
Nanosensors work on the “Nano” scale. “Nano” is a unit of measurement around 10− 9 m. A nanosensor is a device capable of carrying data and information about the behavior and characteristics of particles at the nanoscale level to the macroscopic level. Nanosensors can be used to detect chemical or mechanical information such as the presence of chemical species and nanoparticles or monitor physical parameters such as temperature on the nanoscale. Nanosensors are emerging as promising tools for applications in agriculture. They offer an enormous upgrade in selectivity, speed, and sensitivity compared to traditional chemical and biological methods. Nanosensors can be used for the determination of microbe and contaminants. With the advancement of science in the world and the advent of electronic equipment and the great changes that have taken place in recent decades, the need to build more accurate, smaller and more capable sensors was felt. Today, high-sensitivity sensors are used that are sensitive to small amounts of gas, heat, or radiation. Increasing the sensitivity, efficiency and accuracy of these sensors requires the discovery of new materials and tools. Nano sensors are nanometer-sized sensors that, due to their small size and nanometer size, have such high accuracy and responsiveness that they react even to the presence of several atoms of a gas. Nano sensors are inherently smaller and more sensitive than other sensors.
... For instance, NH 3 detection can be used as a "freshness label" for smart food packaging applications due to its natural release from protein degradation. NH 3 detection is well suited for spoilage detection in protein-rich foods such as meat, fish, and vegetables [16,17]. In the case of H 2 S, it is a volatile gas mainly produced during the degradation process of the sulphur-containing amino acids, so it is a characteristic compound to assess meat spoilage [18,19] as well. ...
QRsens represents a family of Quick Response (QR) sensing codes for in-situ air analysis with a customized smartphone application to simultaneously read the QR code and the colorimetric sensors. Five colorimetric sensors (temperature, relative humidity (RH), and three gas sensors (CO2, NH3 and H2S)) were designed with the aim of proposing two end-use applications for ambient analysis, i.e., enclosed spaces monitoring, and smart packaging. Both QR code and colorimetric sensing inks were deposited by standard screen printing on white paper. To ensure minimal ambient light dependence of QRsens during the real-time analysis, the smartphone application was programmed for an effective colour correction procedure based on black and white references for three standard illumination temperatures (3000, 4000 and 5000 K). Depending on the type of sensor being analysed, this integration achieved a reduction of ∼71 – 87% of QRsens's dependence on the light temperature. After the illumination colour correction, colorimetric gas sensors exhibited a detection range of 0.7-4.1%, 0.7-7.5 ppm, and 0.13-0.7 ppm for CO2, NH3 and H2S, respectively. In summary, the study presents an affordable built-in multi-sensing platform in the form of QRsens for in-situ monitoring with potential in different types of ambient air analysis applications.
... As an indicator of assessing the environmental and indoor pollutants level, NH 3 will also damage the human health once its concentration exceeds 50 ppm for 8 h [1,2]. NH 3 is also an indexed gas for protein-rich food quality assessment, which will be released with the concentration of ppm level during food spoilage process [3,4]. Moreover, the change of NH 3 concentration from human exhaled breath can be used to diagnose some diseases about the liver and lung [5]. ...
High working temperature and the insufficient limits of detection limit the broad applications of semiconductor chemiresistive gas sensors. Herein, pure Bi2MoO6 nanosheets and a series of one-dimensional/two-dimensional (1D/2D) multi-walled CNTs/Bi2MoO6 nanocomposites were developed via a facile hydrothermal route for room-temperature ammonia monitoring. The as-synthesized samples were characterized by various analytical techniques. 0.5 wt% MWCNTs/Bi2MoO6 nanocomposites showed the best sensing properties to 10-50 ppm NH3, including low limit of detection (157 ppb), high response (Ra/Rg = 44.2 @ 50 ppm), good selectivity, reproductivity, and anti-humidity sensing ability. The enhanced gas sensing mechanism was proposed based on the synergetic effect of high-energy crystal facets, modified surface characteristics and p-n heterojunction. Density functional theory (DFT) studies were also carried out to further clarify the gas sensing mechanisms. This work provides a practical approach to design and fabricate high-precision gas sensors working at room temperature.
... The enzyme biosensor is printed on a disposable flexible glove(Figure 15.9a), and the sensor system is integrated with a small electrical interface for operating room detection and real-time communication with smart devices(Figure 15.9b). Similarly, Tang et al.[49] developed a chemiresistive-based gas sensing system for detecting ammonia using a smartphone-based real-time monitoring app for determining the freshness level of food.(Figure 15.10a). ...
... 123 Lithography can be also used to produce highly reproducible structures for biosensing. 124,125 A simpler process of making designs is printing, such as ink jet or screen printing, where the nanomaterials are added to carefully selected fillers, binders, and additives to increase the catalytic activity of the WE. 126 The ratio of the carbonbased [127][128][129] and inorganic materials such as Ag flakes, 130 AgNW, 131 Au, and Cu within a polymer or solvent blend need to be carefully optimized to achieve the desired conductivity and flexibility. ...
The rise of wearable sensors for health monitoring is still at an early stage, though it is rapidly replacing the traditional diagnosis methods with the integration of various breakthroughs in sensor design, advanced materials, sample extraction, and data transmission processes. The use of stretchable electronics and optical devices makes them compatible to use on human skin in varying stress, strain, and in a constantly changing environment. Different types of nanomaterials and polymers in wearable sensors enhance the selectivity and specificity of the biomarker detection. The most important challenges of wearable sensors are sample extraction and storage to monitor the various physiologically important metabolites in body fluids. Recent advances in sensor fabrication on soft substrates are largely focused on the development of reagent-free noninvasive diagnostics for affordable healthcare. In this chapter, the designing and various components of a wearable sensor, and its applications are discussed.
... In order to cope with the timely detection of toxic and hazardous gases and to prevent the related diagnosis of respiratory injuries and diseases, the active development of low-cost, durable, high-performance gas sensors has become the focus of current research [3,4]. With the development of the "Internet of Things" and artificial neural networks, the design of wearable gas sensors provides a promising strategy to broaden the practical applications by combining real-time monitoring and big data analysis, which allows the device applicable to the early detection of any health hazards [5][6][7][8]. Therefore, exploring wearable devices with improved room temperature detection ability ranks as the key to expand the field of gas sensing. ...
Real-time rapid detection of toxic gases at room temperature is particularly important for public health and environmental monitoring. Gas sensors based on conventional bulk materials often suffer from their poor surface-sensitive sites, leading to a very low gas adsorption ability. Moreover, the charge transportation efficiency is usually inhibited by the low defect density of surface-sensitive area than that in the interior. In this work, a gas sensing structure model based on CuS quantum dots/Bi 2 S 3 nanosheets (CuS QDs/Bi 2 S 3 NSs) inspired by artificial neuron network is constructed. Simulation analysis by density functional calculation revealed that CuS QDs and Bi 2 S 3 NSs can be used as the main adsorption sites and charge transport pathways, respectively. Thus, the high-sensitivity sensing of NO 2 can be realized by designing the artificial neuron-like sensor. The experimental results showed that the CuS QDs with a size of about 8 nm are highly adsorbable, which can enhance the NO 2 sensitivity due to the rich sensitive sites and quantum size effect. The Bi 2 S 3 NSs can be used as a charge transfer network channel to achieve efficient charge collection and transmission. The neuron-like sensor that simulates biological smell shows a significantly enhanced response value (3.4), excellent responsiveness (18 s) and recovery rate (338 s), low theoretical detection limit of 78 ppb, and excellent selectivity for NO 2 . Furthermore, the developed wearable device can also realize the visual detection of NO 2 through real-time signal changes.
This article introduces a ternary nanocomposite‐based flexible thin film ammonia sensor developed on transparent polyethylene terephthalate (PET) substrate in the well‐known in situ chemical oxidative polymerization technique. The nanocomposite consists of three different materials: polyaniline (PANI), reduced graphene oxide (rGO), and zinc ferrite (ZF). Keeping the PANI amount constant, seven PANI/rGO/ZF (PRZ) samples are produced by performing stoichiometric variation between rGO and ZF. Later on, various structural, morphological, and spectroscopic analysis of all the composite materials is accomplished with field emission scanning electron microscopy (FESEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible spectroscopy (UV–Vis). The sensing performance of the as‐produced sensors toward ammonia (NH 3 ) is examined in the concentration range from 250 ppb to 100 ppm. The study reveals the excellent sensing ability of the PRZ3 sensor (rGO = 30%, ZF = 20%) achieving minimum and maximum responsivity values of ~51% and ~1052%, respectively, at the lowest (250 ppb) and highest (100 ppm) concentration of ammonia. The sensor also exhibits admirable repeatability, good dynamic responsivity, rapid response (t res ~2.9–5 s), moderately faster recovery (t rec ~37.9–69.7 s), superb linearity against ppm variation ( R ² ~ 0.989), low detection limit (~123 ppb), and exceptional selectivity toward ammonia. The substrate temperature variation divulges that room temperature (30°C) is the ideal temperature for getting outstanding responsivity of the sensor. The study is further accompanied by humidity variation in the incoming air and bending flexibility test of the substrate. A compulsory and legitimate model regarding the sensing mechanism is presented at the end.
The detection of toxic, harmful, explosive, and volatile gases cannot be separated from gas sensors, and gas sensors are also used to monitor the greenhouse effect and air pollution. However, existing gas sensors remain with many drawbacks, such as lower sensitivity, lower selectivity, and unstable room temperature detection. Thus, there is an imperative need to find more suitable sensing materials. The emergence of a new 2D layered material MXenes has brought dawn to solve this problem. The multiple advantages of MXenes, namely high specific surface area, enriched terminal functionality groups, hydrophilicity, and good electrical conductivity, make them among the most prolific gas-sensing materials. Therefore, this review paper describes the current main synthesis methods of MXenes materials, and focuses on summarizing and organizing the latest research results of MXenes in gas sensing applications. It also introduces the possible gas sensing mechanisms of MXenes materials on NH3 , NO2 , CH3 , and volatile organic compounds (VOCs). In conclusion, it provides insight into the problems and upcoming challenges of MXenes materials for gas sensing.
With high demands and rapid development of consumer electronics related to the Internet of Things, various methods have been developed to incorporate different indicators or sensors into packaging for inspecting the safety and quality of food products conveniently. Smart packaging technology is an effective method of monitoring the status of packaged food, thus reducing food waste and food‐borne related illnesses. Food quality can be directly detected from volatile compounds associated with food degradation and/or gas content of the modified atmosphere packaging. Flexible gas sensors based on organic/polymer functional materials have been widely explored to detect trace amounts of gases by exploiting their electrical or mechanical properties. This review first discusses the requirements of gas sensors and system integration for smart packaging. Then, the paper reviews recent advances and strategies of flexible organic/polymer‐based gas sensors and system integration for smart packaging applications. Finally, this review summarizes the challenges and opportunities of flexible gas sensors and system integration for smart packaging applications.
Polyaniline-based conductive polymers are promising electrochemical sensor materials due to their unique physical and chemical properties, such as good gas absorption, low dielectric loss, and chemical and thermal stabilities. The sensing performance is highly dependent on the structure and dimensions of the polyaniline-based conductive polymers. Although in situ oxidative polymerization combined with the self-assembly process has become one of the main processes for the preparation of flexible polyaniline-based gas sensors, how to prepare polyaniline materials into uniformly arranged microwire arrays is still an urgent problem. In this paper, an in-depth study was conducted on the preparation of polyaniline microwire arrays by combining a wettability interface dewetting process and a liquid-film-induced capillary bridges method. The factors influencing the preparation of polyaniline microwire arrays, including solution concentration, template width, evaporation temperature, and evaporation time, were investigated in detail. The wire formation rates were recorded from the results of SEM images. 100% microwires formation rate can be obtained by using a 1.0 mg mL-1 concentration of polyaniline solution and a 10 μm silicon template at an evaporation temperature of 80 °C for 18 h. The prepared microwire arrays can realize sulfur dioxide sensing at room temperature with a response speed of about 20 s and can detect sulfur dioxide gas as low as 1 ppm. Thus, the liquid-film-induced capillary bridge method shows a new possibility to prepare gas sensor devices for insoluble polymers.
Gas sensors are an emerging technology that contributes to the quality and freshness assessment in the food sector. Among the possible techniques to prepare gas sensors, film casting and electrospinning are considered easy and relatively simple methods. The present study aims at investigating the effect of processing on structural, morphological, thermal, and sensitivity properties of gelatin (GEL) based films and mats incorporated or not with anthocyanin (ATH) as a function of the presence of volatile compounds associated with meat spoilage. Both electrospinning process and ATH incorporation induced structural changes in gelatin-based materials, such as decreasing crystallinity as a function of the intermolecular interactions and consequent changes in materials' thermal properties. The sensitivity values of Gel and Gel-ATH mats were respectively, 54% and 45% higher in comparison with their corresponding drop-casting layers. Sensor response showed a prominent correlation with total volatile basic nitrogen. The results suggest the development of a new responsive and biocompatible material for meat quality assessment.
Flexible gas sensors have recently attracted researcher's great attention due to their applications in wearable electronics for different fields like environmental protection, food quality measurement, health supervision, etc. The bulky and complex system of conventional gas sensors hinders their applications in wearable sensing technology. Due to low cost, easy-to-use, and real-time monitoring of harmful gases, there is a rapid increase in the development of flexible gas sensors. With the mechanism of gas sensing and specification of various flexible substrates, this review article comprises a detailed discussion on nanomaterials utilized to fabricate flexible gas sensors. Specifically, all the functional materials are characterized according to their physical and chemical properties. In this article, flexible gas sensor characteristics such as sensitivity, selectivity, response time, operating temperature, and flexibility & bendability profile are discussed in detail for each material. The present review article shows the recent advancements in flexible gas sensors from the sensing material aspect and specifies their applications in various areas. Lastly, the future scope of development, like modification in morphology, functionalization, size alteration, etc., is summarized according to their current status.
NH3 gas in human exhaled breath contains abundant physiological information related to human health, especially chronic kidney disease (CKD). Unfortunately, up to now, most wearable NH3 sensors show inevitable defects (low sensitivity, easy to be interfered by the environment, etc.), which may lead to misdiagnosis of CKD. To solve the above dilemma, a nanoporous, heterogeneous, and dual-signal (optical and electrical) wearable NH3 sensor mask is developed successfully. More specifically, a polyacrylonitrile/bromocresol green (PAN/BCG) nanofiber film as a visual NH3 sensor and a polyacrylonitrile/polyaniline/reduced graphene oxide (PAN/PANI/rGO) nanofiber film as a resistive NH3 sensor are constructed. Due to the high specific surface area and abundant NH3 binding sites of these two nanofiber films, they exhibit good NH3 sensing performance. However, although the visual NH3 sensor (PAN/BCG nanofiber film) is simple without the need of any detecting facilities and quite stable when temperature and humidity change, it shows poor sensitivity and resolution. In comparison, the resistive NH3 sensor (PAN/PANI/rGO nanofiber film) is of high sensitivity, fast response, and good resolution, but its electrical signal is easily interfered by the external environment (such as humidity, temperature, etc.). Considering that the sensing principles between a visual NH3 sensor and resistive NH3 sensor are significantly different, a wearable dual-signal NH3 sensor containing both a visual NH3 sensor and resistive NH3 sensor is further explored. Our data prove that the two sensing signals in this dual-signal NH3 sensor mask can not only work well without interference with each other but also complement each other to improve the sensing accuracy, indicating its potential application in non-invasive diagnosis of CKD.
Wearable electronics and sensors are drawing much attention with the emergence of the internet of things (IoT) and point-of-care testing (POTC) applications. Such wearable devices should be flexible and stretchable to account rather dynamic human motions. Recently, flexible and stretchable gas sensors have emerged as promising technologies to protect workers from exposure to toxic gases. This work presents a detailed study of the impact of strain on the morphology and performance of multi-walled carbon nanotube (MWCNT) based nitrogen dioxide (NO2) gas sensors. To localize the strain effect on the CNT sensing region, rather than electrodes and support structures, we have developed a CNT gas sensor on dog-bone-shaped polydimethylsiloxane (PDMS) substrate. A tensile strain of up to 50% is applied, inducing cracks on the CNT sensing layer and thus altering the electrical resistance of sensors. In addition, a significant shift in the temperature coefficient of resistance (TCR) is observed. Under the assumption that thermally activated carriers overwhelm charge carrier scattering, the TCR of CNTs is altered when strained. Such a strain effect on NO2 gas sensing performance is analyzed in detail. Our study could be applied to developing high-performance flexible and stretchable gas sensors.
Food security is critical for the sustainability of society. The spoilage of stocked food is an ongoing problem that causes significant losses to the global economy. Novel portable analytical platforms that provide timely information on the condition of food stock can support informed decision‐making on the safety of food consumption as well as on maximization of food storage lifetime. Ammonia (NH3) and hydrogen sulfide (H2S) are two of the major harmful gases that are produced due to bacteria activity during the food spoilage process. The timely detection of these gases in food stocks has vital importance to human health. In this review article, the recent progress of conducting polymer based NH3 and H2S gas sensors including sensor device prototypes, their sensing mechanisms, materials and methodologies for sensor fabrication, and their suitability for the development of consumer electronic devices for food spoilage detection are highlighted. This review summarizes the conducting polymer based H2S and NH3 sensors from recent years and analyzes them for their suitability for developing a food spoilage detecting sensor. The paper suggests possible conducting polymer‐based sensors for this application and identifying research gaps where more investigation is needed for food spoilage detection applications.
Recently, various bioelectronic nose devices based on human receptors were developed for mimicking a human olfactory system. However, such bioelectronic nose devices could operate in an aqueous solution, and it was often very difficult to detect insoluble gas odorants. Here, we report a portable bioelectronic nose platform utilizing a receptor protein-based bioelectronic nose device as a sensor and odorant-binding protein (OBP) as a transporter for insoluble gas molecules in a solution, mimicking the functionality of human mucosa. Our bioelectronic nose platform based on I7 receptor exhibited dose-dependent responses to octanal gas in real time. Furthermore, the bioelectronic platforms with OBP exhibited the sensor sensitivity improved by ∼100% compared with those without OBP. We also demonstrated the detection of odorant gas from real orange juice and found that the electrical responses of the devices with OBP were much larger than those without OBP. Since our bioelectronic nose platform allows us to directly detect gas-phase odorant molecules including a rather insoluble species, it could be a powerful tool for versatile applications and basic research based on a bioelectronic nose.
Flexible bifunctional sensors that mimic the function of human skin are essential as they provide critical interacting information with human and environment for intelligentization. However, the problem of interference between sensing signals from different stimuli and the deficiency of comfortability after long-time skin-attaching wearing still exist. Herein, we present an ultrathin and flexible bifunctional sensor based on two measurable parameters of pressure-induced supercapacitance and temperature-induced resistance with neglectable crosstalk between the two. The sensor consists of a planar iontronic supercapacitor underneath a serpentine resistor with assembly of total seven layers integrated on an electrospun thermoplastic polyurethane (TPU)-based nanofiber platform. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based sensing electrodes are patterned by direct ink writing with addition of graphene nanoflakes and Co3O4 nanoparticles to enhance the sensing performance. A high pressure sensitivity (147.19 kPa⁻¹, 0-7 kPa; 4.41 kPa⁻¹, 25-85 kPa) and a high temperature sensitivity (0.040 ℃⁻¹, 25-50 ℃; 0.002 ℃⁻¹, 50-100 ℃) are simultaneously achieved. The sensor also has the advantages of humidity inertness, waterproof ability and air permeability, which is breathable to obtain a wearing comfortability. Decoupled pressure-temperature sensing applications of detecting various subtle pressures with objects of different temperatures are comparatively demonstrated in a wireless and real-time mode. The proposed bifunctional sensor is potential in wearable healthcare monitoring and human-machine interaction.
During the last decades, advancement in the development of different small-sized, portable, low-power, and remote systems has attracted the attention of researchers to employ nonconventional power sources. Piezoelectric and triboelectric nanogenerators are two newly developed technologies for efficient harvesting of environmental, mechanical energy for self-powered systems. This book chapter reviews recent progress in energy harvesting devices based on piezoelectric and triboelectric mechanisms. Different materials and fabrication methods in developing piezoelectric, as well as triboelectric energy harvesting devices, are discussed in this review and fabrication of flexible and hybrid devices for different energy harvesting applications are thoroughly reviewed. In addition, recent research directions being studied, the developing parameters to improve harvester's performance and advance growth in attaining high functionality and durable energy transformation are offered.
The introduction of nanotechnology to the sensing world has opened up a wide spectrum of applications. The flexible sensors formed using a range of nanomaterials have shown high diversity in terms of their physicochemical nature. The micro and nano-sized sensors formed using these nanomaterials showed enhanced attributes in terms of analytical parameters when used in different electrochemical and strain-sensing applications. The mechanical and chemical flexible sensors were formed using nanomaterials having varied sizes, shapes, and structural dimensions. This chapter highlights the deployment of some of the primary types of nanomaterials to form flexible sensors. A classification has been done on the use of some of the nanomaterials like nanoparticles, nanotubes, nanowires and nanosheets, and nanowires, where the synthesis process and application of the flexible sensors have been elucidated. Finally, some of the challenges existing with the current nanotechnology field associated with flexible sensors have been showcased, along with certain possible remedies. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
The ever-growing electronic world has mandated the need to harvest energy in the current world. The total energy needed for these electronic and electrical systems is much more than we produce. This chapter explains the significance of harvesting energy by highlighting the applications that can be driven through the ubiquitous supply of energy. It also highlights a classification of technologies that are available for harvesting energy at macro levels. Three different types of energy harvesting techniques have been showcased, where each of the types has been elucidated in terms of their working mechanism, materials used to develop them and some of the targeted applications. The advantages and demerits associated with each of the shown technologies have also been mentioned in the paper. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
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.
Implantable energy harvesters (IEHs) are the essential and required component for self-powered medical devices. IEHs is employed as the primary power source of implantable medical electronics by harvesting the energy from living organisms such as respiration, heartbeat, and chemical energy from the redox reaction of glucose. In this chapter, IEHs and self-powered implantable medical electronics (SIMEs) are summarized. The typical IEHs are based on ultrasonic or optical energy such as biofuel cells, nanogenerators, electromagnetic generators, and transcutaneous energy harvesting devices. A benefit from these in vivo energy harvesting technologies, SIMEs emerged, including nerve/muscle stimulators, cardiac pacemakers, and physiological sensors. The challenges and potential solutions related to IEHs and SIMEs are also provided.
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.
Research on flexible electronics has grown remarkably in the last decade due to the mechanical limitations of conventional rigid electronics. With the advent of nanotechnology, bulky, thick, and rigid electronic materials have been replaced by nanomaterials that exhibit intrinsic mechanical deformability as well as superior electrical properties. These nanoscale-based soft materials can be envisioned as great assets for the sensing field as conventional sensors usually fail to efficiently capture analytes and, therefore, suffer from poor-quality signal transduction. Herein, we review the literature on nanomaterials-enabled flexible sensors in the past decade, addressing the kinds of nanomaterials that have been used in their fabrication, as well as listing and describing them according to their dimensions (0D, 1D and 2D nanomaterials). Moreover, we discuss some of the different fabrication techniques that have been used in order to obtain flexible sensors, either by fabricating nanocomposites from the combination of nanomaterials and flexible substrates, or by integrating nanomaterials by depositing them on top or between layers of other flexible materials. Then we discuss the advantages of using nanomaterials-assisted flexible sensors, such as simple fabrication processes, or at least the vast number of different techniques that can be applied, the ability to vary the nanomaterials sizes and shapes, elevated sensitivity and selectivity and so on. At last, we bring some examples of applications of nanomaterials-based flexible sensors, more specifically in the fields of electrochemical, strain and electrical sensing, ranging from environmental to medical applications.
The significance of flexible sensors has been extremely significant in the case of energy-harvesting applications. Flexile sensors with varied electromechanical properties have been utilized for piezoelectric, triboelectric and pyroelectric-sensing applications. This chapter concludes the research work explained in the preceding chapters by highlighting some of the essential characteristics of the flexible sensors. The chapter also elucidates the future opportunities of flexible sensors for real-time energy-harvesting and other related applications. It explains some of the possible steps that can be followed to enhance the quality of these sensors so that they can be commercialized and used as point-of-care devices. The availability of the raw materials that are being processed to form the three types of energy-harvesting devices has been showcased with an estimation of their future trend in the next few years. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
The chapter elucidates some of the significant work done on the use of flexible pyroelectric sensing prototypes for energy-harvesting applications. The efficiency of these sensors has been judged based on the diversified temperature variant shown with respect to the disparate materials processed to form the sensors. These sensing prototypes have been used in pure and combined forms, where other major forms like piezoelectric and triboelectric sensors have been conjugated with them for a wide range of applications. Some of the pyroelectric polymers like PVDF have been combined with carbon-based allotropes and metallic nanowires to develop highly efficient prototypes. A few of the major research work related to the deployment of these sensors for temperature sensing and other types of biomedical uses have been highlighted. Finally, some of the existing challenges, along with the probable solutions, have been mentioned in the chapter.
Nanotechnology refers to specifically designed materials as well as devices that possess a minimum of one of their dimensions confined within the range of 1 nm to 100 nm. On specific reference to the electronic properties of materials under the necessary confinement of one of the dimensions, the sub-branch is called nanoelectronics. Nanoelectronics is a collective word that involves specifically tailored nanomaterials with enhanced electronic properties and nanofabrication of such obtained nanomaterials in 2D geometry to fabricate potential assembly of nano devices. Nanoelectronics and nano devices have higher order enhanced storage and much faster operation, such as used in modern day applications of touch-screen laptops, smartphones, tablets, smart watches and many more similar applications.
Nanoelectronics and nano devices are two similar sub-areas of nanotechnology. In contrast, nano devices specifically relate to the fabrication and development of device design, structure, simulation, fabrication methodologies, process optimization and determination of electrical characteristics. This chapter on nanoelectronics is a concise effort to outline, structure and explain various topics in the related field in a nutshell.
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.
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.
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.
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.
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.
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.