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Rapid response flexible humidity sensor for respiration monitoring using nano-confined strategy

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Abstract

Development of wearable devices for continuous respiration monitoring is of great importance for evaluating human health. Here, we propose a new strategy to achieve rapid respiration response by confining conductive polymers into 1D nanowires which facilitates the water molecules absorption/desorption and maximizes the sensor response to moisture. The nanowires arrays were fabricated through a low-cost nanoscale printing approach on flexible substrate. The nanoscale humidity sensor shows a high sensitivity (5.46%) and ultrafast response (0.63 s) when changing humidity between 0 and 13% and can tolerate 1000 repetitions of bending to a curvature radius of 10 mm without influencing its performance. Benefited by its fast response and low power assumption, the humidity sensor was demonstrated to monitor human respiration in real time. Different respiration patterns including normal, fast and deep respiration can be distinguished accurately.

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... Humidity sensors are widely used in many applications, such as environmental monitoring (e.g., indoor climate control in smart houses or industrial production), process control (e.g., high reliability in integrated circuit fabrication), medical equipment, and biotechnology [1][2][3][4][5]. In addition, sensors with a rapid response time are required in areas such as respiratory monitoring and semiconducting process control [6][7][8][9][10]. These scenarios require the response and recovery times of the humidity sensors to be around 1 s [10]. ...
... There are two methods to achieve a fast-response humidity sensor. One way to improve the response speed is to increase the contact area between the probe and the air using specific process technologies, such as new moisture-sensitive materials, ultra-thin moisture-sensitive films, special moisture-sensitive probe structures, and surface treatment of the moisture-sensitive layer [6][7][8][9][10][11][12][13][14][15][16]. Uksong Kang et al. reported a capacitive humidity sensor that used multiple polyimide cylinders with a diameter of several microns as the probe [11]. ...
... The experiments showed that this material-based sensor demonstrated a response time of 0.73 s and a recovery time of 0.52 s. Cheng Zhou et al. proposed a new humidity sensor realized with nanowire arrays [8]. The nanowire arrays were fabricated on a flexible substrate. ...
Article
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Currently, integrated humidity sensors with fast-response time are widely needed. The most commonly used polyimide capacitive humidity sensor has a long response time, which is difficult to meet the need for a fast response. Most studies focusing on technology and materials have a high cost and are difficult to ensure compatability with the CMOS process. The dynamic compensation method can shorten the response time by only adding digital circuits or software processing. However, conventional compensation technology is not suitable for humidity sensors due to temperature coupling. This paper proposes a new dynamic compensation method for humidity sensors based on the decoupling of temperature factors by analyzing the coupling relationship between sensor dynamic characteristics and temperature. Simulations and experiments were used to verify the proposed method. The experimental results show that the proposed method reduces the humidity response time of the sensor by 85.6%. The proposed method can effectively shorten the response time of humidity sensors.
... Hence, nanostructure engineering of PE-DOT:PSS would be crucial for enhancing the gas sensing performance. Typical ways to fabricate nanostructured PEDOT:PSS include nano-confined strategies such as electrospinning [66] and other template methods [67,68]. Furthermore, PEDOT:PSS is printable In most cases, PEDOT:PSS is deposited on IDT electrodes or other substrates by dropcasting or spin-coating. ...
... Hence, nanostructure engineering of PE-DOT:PSS would be crucial for enhancing the gas sensing performance. Typical ways to fabricate nanostructured PEDOT:PSS include nano-confined strategies such as electrospinning [66] and other template methods [67,68]. Furthermore, PEDOT:PSS is printable [10], thus allowing to produce highly uniform films on various flexible substrates such as polyethylene terephthalate (PET) and paper, for which the thickness of the film can be precisely controlled by techniques like inkjet printing. ...
... These methods have a few disadvantages, such as film inhomogeneity, an uncontrollable shape and a low production efficiency. The non-porous structure produced therefrom also results in a long sensing response and recovery time [70], which limits the application of these sensors in the areas such as respiratory monitoring, wherein the response/recovery cycling must be faster (shorter) than a single respiratory period (normally in 3-4 s) [67]. In addition, the three fabrication methods mentioned above are generally suitable for large-area manufacturing of macroscopic devices, but not microscale miniaturized devices, which are otherwise crucial for integration with other functional devices [71]. ...
Article
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Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is a highly important and attractive conducting polymer as well as commercially available in organic electronics, including electrochemical and electronic chemosensors, due to its unique features such as excellent solution-fabrication capability and miscibility, high and controllable conductivity, excellent chemical and electrochemical stability, good optical transparency and biocompatibility. In this review, we present a comprehensive overview of the recent research progress of PEDOT:PSS and its composites, and the application in electrochemical and electronic sensors for detecting liquid-phase or gaseous chemical analytes, including inorganic or organic ions, pH, humidity, hydrogen peroxide (H2O2), ammonia (NH3), CO, CO2, NO2, and organic solvent vapors like methanol, acetone, etc. We will discuss in detail the structural, architectural and morphological optimization of PEDOT:PSS and its composites with other additives, as well as the fabrication technology of diverse sensor systems in response to a wide range of analytes in varying environments. At the end of the review will be given a perspective summary covering both the key challenges and potential solutions in the future research of PEDOT:PSS-based chemosensors, especially those in a flexible or wearable format.
... Similarly, in another work, one-dimensional nanoconfined PEDOT:PSS was utilized as the sensing material. 11 PSS acts as a shell to PEDOT. By water adsorption, PSS swelling is observed and the spacing between PEDOTs increases, leading to an increase in resistivity. ...
... One approach which could potentially be scaled for roll-to-roll production, employed a nanoimprint technique to create nanochannels as templates to guide formation of parallel PEDOT:PSS nanowire arrays directly on the PET substrate upon evaporation of an aqueous solution of PEDOT:PSS. 11 3.3. Unconventional Methods. ...
... Deep, rapid, and normal respiration as well as the apnea periods in the sleep cycle were reported to be distinguished successfully. 11 Similarly, a yarn-shaped sensor was stitched inside a mask. 7 An LC wireless system was formed for signal transmission in order to develop a smart mask. ...
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In the past decade, humidity measurements have ubiquitously gained consideration in the wide range of application paradigms such as industrial predictive maintenance, instrumentation, automation, agriculture, climate monitoring, healthcare, and semiconductor industries. Accurate humidity measurements and cost-effective fabrication processes for large-volume and high-performance sensors with flexible form factors are essential to meet the stringent performance requirements of the emerging application areas. To address this need, recent efforts focus on development of innovative sensing modalities, process technologies, and exploration and integration of new materials to enable low-cost, robust, and flexible humidity sensors with ultrahigh sensitivity and linearity, large dynamic range, low hysteresis, and fast response time. In this review paper, we present an overview of flexible humidity sensors based on distinct sensing mechanisms, employed processing techniques, and various functional sensing layers and substrate materials for specific applications. Furthermore, we present the critical device design parameters considered to be indicative of sensor performance such as relative humidity range, along with a discussion on some of the specific applications and use cases.
... Due to progress in materials science and manufacturing capacity, wearable devices [46][47][48], a type of portable electronic equipment that integrates sensors, have received considerable interest and displayed a great increase in both research and commercialization, including those integrated on watches, bracelets, glasses, clothes, shoes, socks, necklaces, and other accessories, as well as directly attached to the skin of the human body [49,50]. Wearable devices can monitor personal physiological statuses and environmental conditions through detecting health-related physical, chemical, and biological signals [51][52][53][54], such as respiration, temperature, heartbeat, blood pressure, exhaled breath, blood glucose [55][56][57][58][59][60]. Among various wearable sensors, the wearable gas sensor has become an emerging area of critical importance because there is an increasing demand for monitoring exhaled and surrounding air in real-time to achieve breath diagnosis and identify potential environmental hazards, respectively. ...
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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.
... In addition, in vivo applications, the size advantage of 0D nanomaterials is extremely useful for cell uptake and downstream cell processing. However, soft and scalable electronic devices based on one-dimensional nanomaterials have gained rapidly increasing attention in recent years because they can perform real-time non-invasive continuous monitoring (Araki et al., 2019;Tang et al., 2019;Zhai et al., 2019;Zhou et al., 2020). Research into the manufacture of scalable biomedical sensors using 0D nanomaterials is still scarce. ...
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Zero-dimensional (0D) nanomaterials, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), fullerenes, inorganic quantum dots (QDs), magnetic nanoparticles (MNPs), noble metal nanoparticles, upconversion nanoparticles (UCNPs) and polymer dots (Pdots), have attracted extensive research interest in the field of biosensing in recent years. Benefiting from the ultra-small size, quantum confinement effect, excellent physical and chemical properties and good biocompatibility, 0D nanomaterials have shown great potential in ion detection, biomolecular recognition, disease diagnosis and pathogen detection. Here we first introduce the structures and properties of different 0D nanomaterials. On this basis, recent progress and application examples of 0D nanomaterials in the field of biosensing are discussed. In the last part, we summarize the research status of 0D nanomaterials in the field of biosensing and anticipate the development prospects and future challenges in this field.
... This is particularly interesting for the latter, as PEDOT:PSS films are characterized by a grain-like structure, in which PEDOT grains (conductive) are surrounded by PSS (insulating, hydrophilic), which is linked to the decreasing electrical interconnections among PEDOT chains caused by the water absorption (swelling) of PSS [104]. 1D PEDOT:PSS nanowires can reach high sensitivities of 5.46% and an ultra-fast response of 0.63 s [115]. ...
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Chemiresistive sensors have gained increasing interest in recent years due to the necessity of low-cost, effective, high-performance gas sensors to detect volatile organic compounds (VOC) and other harmful pollutants. While most of the gas sensing technologies rely on the use of high operation temperatures, which increase usage cost and decrease efficiency due to high power consumption, a particular subset of gas sensors can operate at room temperature (RT). Current approaches are aimed at the development of high-sensitivity and multiple-selectivity room-temperature sensors, where substantial research efforts have been conducted. However, fewer studies presents the specific mechanism of action on why those particular materials can work at room temperature and how to both enhance and optimize their RT performance. Herein, we present strategies to achieve RT gas sensing for various materials, such as metals and metal oxides (MOs), as well as some of the most promising candidates, such as polymers and hybrid composites. Finally, the future promising outlook on this technology is discussed.
... Since the NaCl-37.5 wt% film has a higher sensitivity than the NaCl-25 wt% film, its signal variation is more distinct despite the slightly slow response/recovery time. These variation rates are in line with the excellent data recently reported on moisture sensors focused on respiratory patterns (Table 1) [33,[68][69][70][71][72][73]. In addition, although the humidity sensitivities of the NaCl-50 and 75 wt% films are significantly high, fast respiratory patterns cannot be observed due to their slow response/recovery times. ...
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A highly polarizable moisture sensor with multimodal sensing capabilities has great advantages for healthcare applications such as human respiration monitoring. We introduce an ionically polarizable moisture sensor based on NaCl/BaTiO3 composite films fabricated using a facile aerosol deposition (AD) process. The proposed sensing model operates based on an enormous NaCl ionization effect in addition to natural moisture polarization, whereas all previous sensors are based only on the latter. We obtained an optimal sensing performance in a 0.5 µm-thick layer containing NaCl-37.5 wt% by manipulating the sensing layer thickness and weight fraction of NaCl. The NaCl/BaTiO3 sensing layer exhibits outstanding sensitivity over a wide humidity range and a fast response/recovery time of 2/2 s; these results were obtained by performing the one-step AD process at room temperature without using any auxiliary methods. Further, we present a human respiration monitoring system using a sensing device that provides favorable and stable electrical signals under diverse respiratory scenarios.
... In the past decade, a great progress of sensors in many fields is achieved. Sensors with induction feature are playing increasing important roles in various fields, such as medical monitoring, industrial production, wearable equipment, internet of things (IoT), etc (Cheng et al., 2020;Kai et al., 2020;Kun et al., 2020;Shao et al., 2020). One important kind of sensors in induction equipment is the flexible temperature sensor. ...
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Temperature reflects the balance between production and dissipate of heat. Flexible temperature sensors are primary sensors used for temperature monitoring. To obtain real-time and accurate information of temperature, different flexible temperature sensors are developed according to the principle of flexible resistance temperature detector (FRTC), flexible thermocouple, flexible thermistor and flexible thermochromic, showing great potential in energy conversion and storage. In order to obtain high integration and multifunction, various flexible temperature sensors are studied and optimized, including active-matrix flexible temperature sensor, self-powered flexible temperature sensor, self-healing flexible temperature sensor and self-cleaning flexible temperature sensor. This review focuses on the structure, material, fabrication and performance of flexible temperature sensors. Also, some typical applications of flexible temperature sensors are discussed and summarized.
... Particularly, the monitoring of human respiration is useful and convenient for evaluating the health condition of patients in the current global COVID-19 pandemic [25]. Currently, various humidity sensors based on graphene and its derivatives [26][27][28][29][30][31][32][33][34][35][36], metal oxides or sulfides [37][38][39][40][41][42][43], and conducting polymers [44,45] have been developed based on the changes in the electrical properties (i.e., capacitance, resistance, and impedance) or weight of these materials after adsorbing water molecules [37,[46][47][48]. Nevertheless, most humidity sensors have suboptimal sensing performance and lack flexibility. ...
Article
Ion-conductive hydrogels with intrinsic biocompatibility, stretchability, and stimuli-responsive capability have attracted considerable attention because of their extensive application potential in wearable sensing devices. The miniaturization and integration of hydrogel-based devices are currently expected to achieve breakthroughs in device performance and promote their practical application. However, currently, hydrogel film is rarely reported because it can be easily wrinkled, torn, and dehydrated, which severely hinders its development in microelectronics. Herein, thin, stretchable, and transparent ion-conductive double-network hydrogel films with controllable thickness are integrated with stretchable elastomer substrates, which show good environmental stability and ultrahigh sensitivity to humidity (78,785.5%/% relative humidity (RH)). Benefiting from the ultrahigh surface-area-to-volume ratio, abundant active sites, and short diffusion distance, the hydrogel film humidity sensor exhibits 2 × 105 times increased response to 98% RH, as well as 5.9 and 7.6 times accelerated response and recovery speeds compared with the bulk counterpart, indicating its remarkable thickness-dependent humidity-sensing properties. The humidity-sensing mechanism reveals that the adsorption of water improves the ion migration and dielectric constant, as well as establishes the electrical double layer. Furthermore, the noncontact human-machine interaction and real-time respiratory frequency detection are enabled by the sensors. This work provides an innovative strategy to achieve further breakthroughs in device performance and promote the development of hydrogel-based miniaturized and integrated electronics. Electronic supplementary material: Supplementary material is available in the online version of this article at 10.1007/s40843-021-2022-1.
... Among them, humidity sensing using SnO2 NWs is known to be able to measure the resistance change with high sensitivity by changing the depletion region caused by oxygen elements and external oxygen molecules on the surface of SnO2 NWs [10,20,21]. Recently, a great deal of research has been conducted to implement a wearable type of sensor, which has evolved from a conventional bulk-type humidity sensor to a flexible thin-film type, and has been used for personal respiration monitoring or skin attachable electronics that analyze the moisture content of the skin [22][23][24][25][26]. Table 1 summarizes the various humidity sensors that have a flexible form and a commercial one, as well. ...
Article
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Humidity, along with temperature, is one of the most important environmental variables in people’s lives. The control of humidity is an important matter that is related to material properties and stability in various industries, as well as basic living. In order to detect humidity, changes in the physical, chemical, and electrical properties of materials related to humidity are used, and studies using various methods are conducted. In this study, a field-effect transistor (FET) device was fabricated on a soft polymer substrate with SnO2 nanowires (NWs), whose electrical properties change in response to water molecules. The SnO2 NWs, synthesized by chemical vapor deposition (CVD), were transferred onto a polymer substrate, using a sliding transfer method. The NW FET device, which was connected to an aluminum (Al)-based radio frequency (RF) receiving antenna, was wirelessly operated as a humidity sensor, based on the change in electrical properties of SnO2 NWs according to the relative humidity (RH). It was configured with a wireless antenna and light emitting diode (LED) indicator to implement a soft wirelessly powered humidity sensor that senses high RH and is expected to be used as a wearable electronic/sensor in the future.
... A wide variety of fabrication processes for humidity sensors are reported in literature (da Costa and Choi, 2020;Delipinar et al., 2021). Inkjet and screen-printing processing techniques are well standardized as mass fabrication techniques (Molina-Lopez et al., 2012;Zhang et al., 2018;Zhou et al., 2020). Spray coating is another approach employed in literature in the fabrication of humidity sensors (Lipomi et al., 2011;Kim and Yun, 2013;Bu et al., 2016;Kim et al., 2018). ...
Article
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Flexible and thin-film humidity sensors are currently attracting the attention of the scientific community due to their portability and reduced size, which are highly useful traits for use in the Internet o Things (IoT) industry. Furthermore, in order to perform efficient and profitable mass production, it is necessary to develop a cost-effective and reproducible fabrication process and materials. Green fabrication methods and biodegradable materials would also minimize the environmental impact and create a sustainable IoT development. In this paper, flexible humidity sensors based on a common salt (NaCl) sensing layer are reported. Our sensors and the fabrication techniques employed, such as dip and spray coating, provide a biodegradable, low cost, and highly reproducible device. One of the sensors reported presents a typical resistive behaviour from 40% RH up to 85% RH with a sensitivity of −0.21 (Z/%RH). The performance of the sensors obtained with several fabrication techniques is studied and reported at multiple frequencies from 100 Hz to 10 MHz, showcasing its versatility and robustness.
... These flexible devices, which include sensors, are considered to be the technological basis of the IoT [1]. Previous studies have fabricated these flexible humidity sensors based on sensing materials such as cellulose paper [2], polytetrafluoroethylene (PTFE) [3], polypyrrole [4], poly(3,4-ethylenedioxythiophene) (PEDOT) [5], sodium niobate (NaNbO 3 ) [6], cupric oxide (CuO) [7], as well as, various types of carbon materials such as carbon nanotubes [8][9][10], reduced graphene oxide (rGO) [11][12][13], graphene oxide (GO) [14,15] and graphene [16], either as stand-alone materials or in the form of composites. ...
Article
In this study, we have demonstrated the humidity sensitivity of graphite pencil marks sensing material drawn on paper. The fabricated sensing devices (sensors) were characterized for their humidity sensitivity by measuring the resistance changes across the pencil marks. In order to improve the humidity sensitivity of the sensing material, ethanol chemical treatment was applied on the pencil marks to increase their surface hydrophilicity. Sensors with different levels of intrinsic resistances were also prepared and tested. Results showed that the ethanol-treated sensors have better humidity sensitivities and the intrinsic resistances of the sensors were directly proportional to their humidity sensitivity. To evaluate this carbon-based sensing material, the humidity sensing characteristics of the pencil graphite were gauged with other forms of carbon materials that have been reported in previous studies, such as carbon quantum dots film, carbon nanoparticles, carbon nanotubes, graphene oxide and graphene.
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It is of great significance to exploit a simple, cost-effective and environmentally friendly preparation method of multifunctional humidity sensors. However, most humidity sensors need complex manufacturing processes, high cost and narrow usage range. Herein, humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC) modified cellulose paper via a facile solution method were fabricated, among which the paper is used for the purpose of the humidity sensing material and the sensor substrate. The sensitivity of the obtained sensor was improved by the modification of EPTAC, the response time was decreased to 25 s, which is equivalent to the first-rate paper-based humidity sensors. In addition, the paper-based humidity sensor is provided with well flexibility and biocompatibility, and it exhibits multifunctional applications in respiratory monitoring, non-contact switch and skin humidity monitoring. The low cost and facile preparation technique in this work could provide a useful strategy for developing multifunctional humidity sensor.
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italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Goal: The SARS-CoV-2 viral infection could cause severe acute respiratory syndrome, disturbing the regular breathing and leading to continuous coughing. Automatic respiration monitoring systems could provide the necessary metrics and warnings for timely intervention, especially for those with mild symptoms. Current respiration detection systems are expensive and too obtrusive for any large-scale deployment. Thus, a low-cost pervasive ambient sensor is proposed. Methods: We will posit a barometer on the working desk and develop a novel signal processing algorithm with a sparsity-based filter to remove the similar-frequency noise. Three modes (coughing, breathing and others) will be conducted to detect coughing and estimate different respiration rates. Results: The proposed system achieved 97.33% accuracy of cough detection and 98.98% specificity of respiration rate estimation. Conclusions: This system could be used as an effective screening tool for detecting subjects suffering from COVID-19 symptoms and enable large scale monitoring of patients diagnosed with or recovering.
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Nitrite is a toxic substance, when excessive nitrite enters the human body, it will be seriously harmful to human. At present, the detection methods of nitrite are complicated to operate and require expensive detection instruments. Therefore, an effective, fast and highly selective nanogold film interdigital electrode sensors that can detect nitrite easily and quickly is developed in the work. Firstly, the variation of the sensitivity of nanogold film nitrite sensors with concentrations (1 mol/L, 10−1 mol/L, 10−2 mol/L, 10−3 mol/L, 10−4 mol/L, and 10−5 mol/L) was measured by experiments. Then, Chrome-black T was modified to the surface of the nanogold film interdigital electrodes by electrochemical polymerization, and the film of chrome-black T had affinity for nitrite ions, so nitrite ions were enriched on the sensor surface. The change law of the impedance signal of the modified nanogold film nitrite sensors after being added to different concentrations of sodium nitrite solution were also concluded. The study demonstrates that the larger the concentration of sodium nitrite solution is added to the modified interdigital electrodes, the smaller impedance and resistance of the modified interdigital electrodes are reflected. Finally, specificity of the modified interdigital electrode sensors has been demonstrated. The novel interdigital electrode sensors can detect the concentration of nitrite solution conveniently and quickly with only 30 s. Therefore, the prospect of applying the novel nanogold film interdigital electrode sensors to the detection of nitrite in blood, body fluid, food and drinking water is promising.
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The current ongoing outbreak of Coronavirus Disease 2019 (COVID-19) has globally affected the lives of more than one hundred million people. RT-PCR based molecular test is recommended as the gold standard method for diagnosing current infections. However, transportation and processing of the clinical sample for detecting virus require an expert operator and long processing time. Testing device enables on-site virus detection could reduce the sample-to-answer time, which plays a central role in containing the pandemic. In this work, we proposed an intelligent face mask, where a flexible immunosensor based on high density conductive nanowire array, a miniaturized impedance circuit, and wireless communication units were embedded. The sub-100 nm size and the gap between the neighbored nanowires facilitate the locking of nanoscale virus particles by the nanowire arrays and greatly improve the detection efficiency. Such a point-of-care (POC) system was demonstrated for coronavirus ‘spike’ protein and whole virus aerosol detection in simulated human breath. Detection of viral concentration as low as 7 pfu/mL from the atomized sample of coronavirus aerosol mimic was achieved in only 5 mins. The POC systems can be readily applied for preliminary screening of coronavirus infections on-site and may help to understand the COVID-19 progression while a patient is under prescribed therapy.
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For a long time, humidity sensors have been mainly used in detecting humidity of ambient conditions, such as industry, agriculture, and smart home. With the development of wearable electronic systems, humidity sensors have attracted great attention in human body-related (HBR) humidity detection (such as respiratory behavior, speech recognition, skin moisture, non-contact switch, and diaper monitoring). Therefore, significant efforts have been recently devoted to the development of HBR humidity sensors. Although remarkable achievements have been made in this field, many challenges still exist. Herein, we review and analyze the recent advances in HBR humidity sensors. Initially, we introduced the basic concept. Then, the various applications of humidity sensors for HBR humidity detection are systematically summarized and discussed. Finally, combined with the research progress of the HBR humidity sensor, the challenges in this field are prospected. We expect that this critical review will provide great insight and direct the research prospectus of the HBR humidity sensors.
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The discrimination of humidity in exhaled breath is of utmost importance to turn breath analysis into an efficient noninvasive tool for early diagnosis or treatment monitoring of several diseases. Herein, by assembling different ratios of the conductive poly(3,4‐ethylenedioxythiophene): polystyrene sulfonate with the polymer matrix polyethylene oxide (PEO), humidity chemiresistor‐based sensors are designed and investigated. The testing results display a broad relative humidity detection range (6–92%), repeatability, reproducibility, and good reversibility. Meanwhile, the sensors possess good reliability for distinct temperatures and in the presence of typical volatile organic compounds found in human exhaled air. The hygroscopic idiosyncrasy of PEO is attributed to be the main responsible for the high sensibility toward humidity. In a proof‐of‐principle for detection of respiration humidity, the outcome shows the ability of the chemiresistors to detect the humidity variation in a real case of breath exposure up to 2 s intervals. The 30 d trial of stability readings shows a standard deviation of only 2.6%. These sensing devices appear as a new array component able to distinguish moisture from biomarkers of diagnosed diseases in breath analysis. With an increasing search for noninvasive tools to diagnose diseases through breath, the discrimination of water from other species in breath is important. Herein, a novel chemiresistor from poly(3,4‐ethylenedioxythiophene): polystyrene sulfonate with polyethylene oxide shows its potential as a humid sensor with broad detection range, repeatability, reproducibility, and reversibility that can serve as an array for an electronic nose.
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C and N have been co-doped to improve the humidity sensing of zirconia, which shows fast response, short recovery and good repeatability.
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We report a bio‐inspired continuous wearable respiration sensor modeled after the lateral line system of fish which is used for detecting mechanical disturbances in the water. Despite the clinical importance of monitoring respiratory activity in humans and animals, continuous measurements of breathing patterns and rates are rarely performed in or outside of clinics. This is largely because conventional sensors are too inconvenient or expensive for wearable sensing for most individuals and animals. The bio‐inspired air‐silicone composite transducer is placed on the chest and measures respiratory activity by continuously measuring the force applied to an air channel embedded inside a silicone‐based elastomeric material. The force applied on the surface of the transducer during breathing changes the air pressure inside the channel, which is measured using a commercial pressure sensor and mixed‐signal wireless electronics. We extensively characterized the transducer produced in this work and tested it with humans, dogs, and laboratory rats. The bio‐inspired air‐silicone composite transducer may enable the early detection of a range of disorders that result in altered patterns of respiration. The technology reported can also be combined with artificial intelligence and cloud computing to algorithmically detect illness in humans and animals remotely, reducing unnecessary visits to clinics. This article is protected by copyright. All rights reserved
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Flexible sensors, as a kind of indispensable branch of flexible electronics, are garnering substantial in medical and industrial applications. Ever‐evolving advances in nanowires in their myriad forms have fueled many of the developments in this field. However, recent researches have extensively focused on the intrinsic properties of these nanomaterials, rationally designed structures, which are pivotal in sensing performance, to a large extent, are undervalued. Hereon, the latest advances in the structure design, together with controlled fabrication of nanowires for better sensing performance are highlighted. In specific, nanowires are classified according to morphologies and hybrid forms and their corresponding fabrication methodologies and influence on sensing properties are briefly discussed. Then, construction strategies for nanowire‐based sensors, including materials assembly and macroscopical design are systematically summarized. Subsequently, the characteristics and advantages of flexible sensors induced by various nanowires, including physical/physiological/multifunctional parameters sensing are reflected in the application examples. Finally, conclusions and challenges are presented for the development of nanowire‐based flexible sensors, as well as frontier strategies especially bionic design. This review is aimed at providing a valuable and systematic understanding of nanowires in sensing system and then serves as inspiration for intelligent designs in flexible future electronics. Nanowires offer plentiful morphologies and combined forms, which has significant contributions to the flexible sensors by controlling the sensing performance. Likewise, the geometric structures and interconnections formed by various nanowires and substrates play key roles in the performance of flexible sensors as well. This review highlights the effects of structure designs of nanowires and geometric structures on the performance of nanowire‐based sensors.
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Thin-film microdevices can be applied to various wearable devices due to their high flexibility compared to conventional bulk-type electronic devices. Among the various microdevice types, many IoT-based sensor devices have been developed recently. In the case of such sensor elements, it is important to control the surrounding environment to optimize the sensing characteristics. Among these environmental factors, temperature often has a great influence. There are cases where temperature significantly affects the sensor characteristics, as is the case for gas sensors. For this purpose, the development of thin-film-type micro-heaters is important. For this study, a wirelessly driven thin-film micro-heater was fabricated on the flexible and stretchable elastomer, a polydimethylsiloxane (PDMS); the antenna was optimized; and the heater was driven at the temperature up to 102 degrees Celsius. The effect of its use on gas-sensing characteristics was compared through the application of the proposed micro-heater to a gas sensor. The heated SnO2 nanowire gas sensor improved the performance of detecting carbon monoxide (CO) by more than 20%, and the recovery time was reduced to less than half. It is expected that thin-film-type micro-heaters that can be operated wirelessly are suitable for application in various wearable devices, including those for smart sensors and health monitoring.
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Humidity sensors are widely used in domestic and industrial environments. The humidity sensing requires the sensor to be both flexible and stable. However, challenges still exist for the realization of efficient flexible humidity sensors. Herein, α‐In 2 Se 3 nanosheet‐based humidity sensors both on PET and SiO 2 /Si substrates are fabricated. The humidity sensing behaviors are investigated in a wide relative humidity (RH) range frome 11%RH to 97%RH at room temperature. Compared with the properties of a silicon‐based humidity sensor based on α‐In 2 Se 3 nanosheet, the flexible humidity sensor based on α‐In 2 Se 3 nanosheet exhibit higher sensitivity of 2.38×10 3 %, shorter response and recovery time of 9 s and 13 s. Due to the lower activation energy of the flexible humidity sensor, so that the sensitivity of the flexible humidity sensor being 25 times higher than that of the silicon‐based humidity sensor. These results indicate that α‐In 2 Se 3 nanosheet may be a potential humidity‐sensing material for fabricating humidity sensors with high performance, and the flexible humidity sensor based on α‐In 2 Se 3 nanosheet has great potential in flexible wearable electronic devices.
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Self-supported polymer films were fabricated by the thiol-ene click cross-linking reaction in this work. The cross-linked frameworks were used to guarantee the stability the films. The hydrophilic monomer with different contents were introduced into the self-supported thick films and uniformly dispersed in the polymer frameworks. The interdigitated electrodes were screen printed with silver paste on the self-supported films to obtain humidity sensors. Herein, the self-supported film acts as both the sensor substrate and the humidity-sensing material. The humidity sensing performances of the obtained sensors were systematically researched. By optimizing the ratio of hydrophilic monomer in the polymer films, the sensitivities of the sensors were enhanced from 1.58 to 103.75 (in the humidity from 11% RH to 95% RH), the response under low RH environment was significantly improved with good linearity. The response/recovery times of the sensor within the humidity range are measured to be 12.5 s and hundreds of seconds. The prepared flexible sensors possess certain mechanical properties, and exhibit good stability under bending and long-term tests up to 60 days. The applications of the as-prepared sensor in the detection of non-contact human skin humidity, human respiration and relative humidity of green plant were explored. The sensor shows excellent sensing performance in various applications and indicates the potential application in wearable and multifunctional devices.
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The development of high-performance humidity sensors to cater for a plethora of applications, ranging from agriculture to intelligent medical monitoring systems, calls for the selection of a reliable and ultrasensitive sensing material. A simplistic device architecture, robust quantification of ambient relative humidity (% RH), and compatibility with the contemporary integrated circuit technology make a bimodal (capacitive and resistive) surface-type sensor to be a prominent choice for device fabrication. Herein, we have proposed and demonstrated a facile realization of a 5,10,15,20-tetraphenylporphyrinatonickel (II)-zinc oxide (TPPNi-ZnO) nanocomposite-based bimodal surface-type % RH sensor. The TPPNi macromolecule and ZnO nanoparticles have been synthesized by an eco-benign microwave-assisted technique and a thermal-budget chemical precipitation method, respectively. It is speculated from the morpohological study that specific surface area improvement, via the provision of ZnO nanoparticles on micro-pyramidal structures of TPPNi, may reinforce the sensing properties of the fabricated humidity sensor. The relative humidity sensing capacitive and resistive characteristics of the sensor have been monitored in 40-85% relative humidity (% RH) bandwidth. The fabricated sensor under the biasing conditions of 1 V of applied bias (V rms) and 500 Hz AC test frequency exhibits a significantly higher sensitivity of 387.03 pF/% RH and 95.79 kΩ/% RH in bimodal operation. The average values of both the response and recovery times of the capacitive sensor have been estimated to be ∼30 s. It has also been debated why this high degree of sensitivity and considerable reduction in response/recovery time has been obtained. In addition, the intense and wide bandwidth spectral response of the TPPNi-ZnO nanocomposite indicates that it may also be utilized as a potential light-harvesting heterostructured nanohybrid in future studies.
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Herein, surfactant-assisted PANI nanorods was synthesized via the solid-state synthesis method at different concentrations of sodium lauryl sulfate (SLS). Upon the addition of SLS, the average rod diameter of PANI decreased from 72 ± 6 nm to 58 ± 6 nm. The electrical conductivity of PANI increased by three folds upon the addition of SLS (8.2 S.cm-1). Further, the presence of SLS modulated the PANI chains, which facilitated enhancing the thermal stability. PANI/SLS-based humidity sensor was built on a paper substrate through doctor blade coating technique and its performance metrics were accessed at different humidity conditions. PANI/SLS coated paper-based humidity sensor exhibited excellent response along with fast response/recovery characteristics. Improved electrical conductivity and high surface area of SLS assisted PANI nanorods readily interacted with the water molecules, which significantly increased the sensitivity of the sensor upto 31.5 kohm/%RH (linearity = 0.99). Furthermore, the sensor showed excellent response under physiological conditions such as respiration monitoring and skin moisture detection. The ultrasensitive humidity sensing performance of PANI/SLS coated paper with good skin-friendly characteristics makes it a potential material for multipurpose smart wearable devices.
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Flexible humidity sensor, a promising device for monitoring humidity, is widely used for patients’ respiratory analysis due to its portability and cost-effectiveness. However, through intrinsic rigid nature of traditional flexible substrate such as polymer and paper, the fiber-based device exhibits great application potential in wearable platform. In this work, a fabric humidity sensor based on diamine-decorated graphene oxide/mesoporous silica nanospheres (GONH2/mSiO2) is designed via screen printing. The decoration of diamine is introduced to improve the hydrophilic properties of GO, and the mesoporous structure of mSiO2 is employed to adjust the adsorption and desorption of water molecules. As a result, the fabric humidity sensor exhibits fast response (≈12.6 s), high sensitivity (14.8 MΩ/% relative humidity (RH)), and low hysteresis (2.71% RH) at the humidity interval from 23% to 97% RH. Owing to the GONH2/mSiO2 composite materials screen-printed on the medical mask, the fabric humidity sensor can delicately detect respiratory rates, mouth and nose breathing, as well as coughing. Moreover, the GONH2/mSiO2 humidity sensor is applied for noncontact sensation (such as the detection of fingertip approaching). These properties allow the sensor to serve as excellent wearable electronics for real-time and successive human health detecting.
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In material synthesis, nanoconfinement acts both as a physical reactor to tune the shape and size of nanomaterials, and as a chemical microenvironment for the nucleation and growth of nanoconfined substances, resulting in unique material properties. This nanoconfinement effect has been extensively applied to synthesize materials for hydrogen storage, catalysis and separation for environmental protection. Here, we review methods to construct nanoconfined space in carbon materials, metal–organic frameworks, mesoporous silica, porous organic polymers and MXenes, a class of two-dimensional inorganic compounds. We discuss nanoconfinement for enhanced adsorption with focus on covering size and dispersion, crystallization and stability, confined water and coordination.
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HIGHLIGHTS • The morphology of PEDOT:PSS, including in the forms of aqueous dispersions, solid films, and hydrogels, is outlined, and the application potential of PEDOT:PSS hydrogels is described. • Fabrication techniques for PEDOT:PSS-based devices are introduced, including coating, printing, conventional lithography, and soft lithography. • The latest developments in four main categories of PEDOT:PSS-based physical sensors, for humidity, temperature, pressure, and strain, respectively, are introduced. • The development prospects for PEDOT:PSS, from materials to fabrication techniques to physical sensors, are outlined.
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Wearable sensors allow for portable, long-term health monitoring in natural environments. Recently, there has been an increase in demand for technology that can reliably monitor respiration, which can be indicative of cardiac diseases, asthma, and infection by respiratory viruses. However, to date, the most reliable respiration monitoring system involves a tightly worn chest belt that is not conducive to longitudinal monitoring. Herein, we report that accurate respiration monitoring can be effected using a fabric-based humidity sensor mounted within a face mask. Our humidity sensor is created using cotton fabrics coated with a persistently p-doped conjugated polymer, poly(3,4-ethylenedioxythiophene):chloride (PEDOT-Cl), using a previously reported chemical vapor deposition process. The vapor-deposited polymer coating displays a stable, rapid, and reversible change in conductivity with an increase in local humidity, such as the humidity changes experienced within a face mask as the wearer breathes. Thus, when integrated into a face mask, the PEDOT-Cl-coated cotton humidity sensor is able to transduce breaths into an electrical signal. The humidity sensor-incorporated face mask is able to differentiate between deep and shallow breathing, as well as breathing versus talking. The sensor-incorporated face mask platform also functions both while walking and sitting, providing equally high signal quality in both indoor and outdoor contexts. Additionally, we show that the face mask can be worn for long periods of time with a negligible decline in the signal quality.
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Microwave sensors based on microstrip antennas are promising as wearable devices because of their flexibility and wireless communication compatibility. However, their sensitivity is limited due to the reduced sensor size and the potential of biochemical monitoring need to be explored. In this work, we present a new concept to enhance the microwave signals using of nanostrip-based metamaterials. The introduction of the nanostrip structures were achieved by theory and simulations. Experiments proof their enhancement to the electric field and sensing response in the characteristic gigahertz (GHz) wave band. Ordered nanostrips were fabricated on plastic substrate through simple nanoscale printing approach. Glucose oxidase is directly doped into the nanostrips, which enables a flexible wearable enzymatic biosensor for glucose sensing. Sensing experiments demonstrated that the nanostrip biosensor gives excellent performance for glucose detection, including high sensitivity, fast response, low detection limit, high affinity, and low power consumption. The applicability of the nanostrip-based sensor as wearable epidermal device for real-time noninvasive monitoring of glucose in sweat is verified as well.
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Manufacturing is the primary industry promoting economic and social development. For the past 30 years, the global trends of preciseness and device miniaturisation have promoted manufacturing to the micro (μ) and nano (η) scale. Identification of the most promising micro-nano manufacturing technologies (MNMT) is of interest to industry, academia and private and national science investing foundations. Considering the exponential broadening of the research area and an enormous volume of literature, providing an overview of the state of the art is far beyond the scope of a technical review paper. This study performs bibliometric analysis of a stream of academic literature devoted to μ- and η-machining. The main goals of the analysis are to assess the current core and trends in the field of MNMT. Literature and citation statistics from 1988 were collected from the Web of Science, Google Scholar, Scopus, Engineering Village, ScienceDirect and SpringerLink databases and were then analysed and illustrated with Microsoft Excel and VOSviewer software. The top keywords, articles, journals, authors, universities and countries were identified according to different parameters. The index of normalised influence was offered to evaluate the top element in each category. We observed that the most powerful keywords were present in well-known articles published in prominent journals by authoritative scientists at leading universities in the countries that are most actively engaged in MNMT. The implications of the research outcomes for investors and academicians are summarised in the conclusion. Keywords: Bibliometric analysis, Micro-machining, Nano-machining, Top, Citations
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Poly(3,4-ethylenedioxythiophene)–polystyrenesulfonate and manganese oxide (PEDOT:PSS/MnO2) hybrids were prepared via a facile solvothermal method coupled with an oxidative polymerization route. The effects of the reaction temperature and the KMnO4-to-organic monomer (3,4-ethylenedioxythiophene, EDOT) ratio on the morphology, structure, and electrochemical properties of the materials were investigated. The optimized composites comprised homogeneous nanorod-like structures and exhibited overwhelmingly high conductivity (36 S cm−1) and superior supercapacitance—more specifically, they exhibited high-rate capability. The electrochemical properties of the nanocomposites were investigated using cyclic voltammetry and galvanostatic charge–discharge cycling. The prepared hybrids showed a high capacitance of 365.5 F g−1 at a current density of 1 A g−1, a good rate performance of 325.4 F g−1 at 20 A g−1 (capacitance retention of 89%), and excellent cycling stability with approximately 80% capacitance retention after 2000 cycles at a current density of 5 A g−1 in a 6 M KOH aqueous electrolyte.
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Alginate nanofibers assembled with sliver nanoparticles throughout the whole nanofiber were fabricated by three steps including electrospinning of Na-alginate nanofibers, ion exchange between the sodium and silver ions, and in situ reduction of silver nanoparticles. The content, distribution and size of the nanoparticles are controllable by tuning reaction conditions. Ag/alginate nanofibers exhibit good humidity sensitivity in a wide humidity range from ambient RH (20%) to 85% RH. Interestingly, these humidity sensors can be attached to a 3M-9001V mask for monitoring human breath during exercise and emotion changes, and this smart exhibits accurate and continuous human-breath tracking no matter how fast or slow as well as how deep or shallow. The obtained frequencies of respiration during normal, running, delight and sadness conditions were 16, 13, 14 and 8 times min-1, respectively. Moreover, the signal waveform obtained under emotion changes is distinguishable, implying its potential applications in lie detection and interrogation. Thanks to this smart mask could accurately capture the rate and depth of the respiration, providing an effective, low-cost and convenient approach for tracking respiration, it was utilized as smart fabrics in avoiding sleep apnea.
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Development of flexible devices for continuous respiration monitoring has been fueled up recently due to their great importance for constructing wearable healthcare systems. However, there is no report on a silk fabric-based device for precise detection of human respiratory rate and depth. In this work, a silk fabric-based respiration sensor was fabricated by successive electroless plating of conductive interdigital electrodes and spray-coating of a graphene oxide (GO) sensing layer. Surface morphologies of the devices were characterized to show the construction of the sensor. The uniform surface distribution of GO nanosheets was exhibited using the Raman mapping method. After optimization, the as-prepared device could accurately detect the human respiration rate and effectively differentiate normal, deep as well as fast breathing. The flexibility test indicates that the sensor can tolerate 2500 times of bending and twisting without influencing its performance. Moreover, by designing the spray-coating mask, GO layers with various patterns could be deposited to achieve both functionality and aesthetics. This work not only develops a silk fabric-based sensor for potential applications in assessing of human basic health-status, but also provides a facile approach to preparing textile-based wearable electronic devices.
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Fully printed humidity sensors based on two dimensional (2D) materials are described. Monolayer graphene oxide (GO) and few-layered black phosphorus (BP) flakes were dispersed in low boiling point solvents suitable for inkjet printing. The humidity sensors were fabricated by printing of GO and BP sensing layers on printed silver nanoparticle electrodes. The electrical response of the GO and BP sensors to humidity levels ranging from 11 to 97% RH, which revealed high capacitance sensitivity of 4.45 × 10⁴ times for the GO sensor and 5.08 × 10³ times for the BP sensor at 10 Hz operation frequency. Response/recovery times of the GO and BP sensor were measured to be 2.7/4.6 s and 4.7/3.0 s respectively. These sensors also showed sensitive and fast response to a proximal human fingertip, giving potential applications in contactless switching.
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Novel capacitance-type humidity sensors based on MoS2/Ag composite films with a simple preparation method were proposed. The sensing characteristics of sensors against relative humidity were investigated, and the test results demonstrated that the humidity sensitivity of the MoS2/Ag-based sensors was significantly enhanced, which is ten times that of the pure MoS2-based humidity sensors. Meanwhile, this kind of sensors exhibited fast response speed capable of detecting the human breath. Furthermore, complex impedance spectroscopy was discussed to understand the sensing mechanisms of MoS2/Ag-based sensors.
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Respiration rate is known to correlate with aspects of psychological well-being, and attention to respiration is a central component of mindfulness meditation training. Both traditional contemplative systems and recent empirical evidence support an association between formal mindfulness practice and decreased respiration rate. However, the question of whether long-term mindfulness training is associated with stable, generalized changes in respiration has yet to be directly investigated. We analyzed respiration patterns across multiple time points, separated by two months or more, in a group of long-term mindfulness meditation practitioners (LTMs, n = 31) and a matched group of non-meditators (Controls, n = 38). On average, LTMs showed slower baseline respiration rate (RR) than Controls. Among LTMs, greater practice experience was associated with slower RR, independently of age and gender. Furthermore, this association was specific to intensive retreat practice, and was not seen for routine daily practice. Full days of meditation practice did not produce detectable changes in baseline RR, suggesting distal rather than immediate effects. All effects were independent of physiological characteristics including height, weight, body-mass index and waist-hip ratio. We discuss implications for continued study of the long-term effects of mindfulness training on health and well-being.
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The effect of temperature and humidity on the electrical properties of thin films based on multi-walled carbon nanotubes (MWCNTs) dispersed in sodium dodecylbenzene sulfonate (SDBS) and mixed with poly (3,4-ethylene dioxythiophene)–poly (4-styrenesulfonate) (PEDOT:PSS) were investigated systematically. The change in DC-resistivity was measured by 4-wire technique as a function of the temperature and the relative humidity (RH). The investigation of temperature influence shows semiconducting behavior in the temperature range from 20 °C to 80 °C. This behavior is due to the tunneling barrier, which is expected to dominate the overall film resistance in this temperature range. Moreover, the investigation of humidity effects at temperatures up to 60 °C shows that the resistivity increases exponentially until 70% RH and then it starts to decrease sharply because of development of water layer on PEDOT:PSS film. This effect plays a minor role at high working temperature e.g. 70 °C. Below the saturation point, the films act as a humidity sensor with high sensitivity around ∼0.07%RH.
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Continuous respiratory monitoring is important to assess adequate ventilation. We present a fiber optic-based smart textile for respiratory monitoring able to work during Magnetic Resonance (MR) examinations. The system is based on the conversion of chest wall movements into strain of two fiber Bragg grating (FBG) sensors, placed on the upper thorax (UT). FBGs are glued on the textile by an adhesive silicon rubber. To increase the system sensitivity, the FBGs positioning was led by preliminary experiments performed using an optoelectronic system: FBGs placed on the chest surface experienced the largest strain during breathing. System performances, in terms of respiratory period (TR), duration of inspiratory (TI) and expiratory (TE) phases, as well as left and right UT volumes, were assessed on four healthy volunteers. The comparison of results obtained by the proposed system and an optoelectronic plethysmography highlights the high accuracy in the estimation of TR, TI, and TE: Bland-Altman analysis shows mean of difference values lower than 0.045 s, 0.33 s, and 0.35 s for TR, TI, and TE, respectively. The mean difference of UT volumes between the two systems is about 8.3%. The promising results foster further development of the system to allow routine use during MR examinations.
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Poly(3,4-ethylenedioxythiophene)/Poly(styrenesulfonate) (PEDOT/PSS) is a widely used conductive polymer in the field of flex- ible electronics. The ways its microstructure changes over a broad range of temperature remain not well understood. This paper describes microstructure changes at different temperatures, and correlates microstructure with its physical properties (mechanical and electrical). We used High-Angle Annular Dark-Field Scanning Electron Microscopy (HAADF-STEM) combined with elec- tron energy loss spectroscopy (EELS) to determine the morphology and element atomic ratio of the film at different temperatures. These results together with the Atomic Force Microscopy (AFM) analysis, provide the foundation for a model of how temper- ature affects the microstructure of PEDOT/PSS. Moreover, dynamic mechanical analysis (DMA) and electrical characterization were performed to analyze the microstructure and physical property correlations
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In this paper, a textile-based respiratory sensing system is presented. Highly flexible polymeric optical fibres (POFs) that react to applied pressure were integrated into a carrier fabric to form a wearable sensing system. After the evaluation of different optical fibres, different setups were compared. To demonstrate the feasibility of such a wearable sensor, the setup featuring the best performance was placed on the human torso, and thus it was possible to measure the respiratory rate. Furthermore, we show that such a wearable system enables to keep track of the way of breathing (diaphragmatic, upper costal and mixed) when the sensor is placed at different positions of the torso. A comparison of the results with the output of some commercial respiratory measurements devices confirmed the utility of such a monitoring device.
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We propose a new body sensor for extracting the respiration rate based on the amplitude changes in the body surface potential differences between two proximal body electrodes. The sensor could be designed as a plaster-like reusable unit that can be easily fixed onto the surface of the body. It could be equipped either with a sufficiently large memory for storing the measured data or with a low-power radio system that can transmit the measured data to a gateway for further processing. We explore the influence of the sensor’s position on the quality of the extracted results using multi-channel ECG measurements and considering all the pairs of two neighboring electrodes as potential respiration-rate sensors. The analysis of the clinical measurements, which also include reference thermistor-based respiration signals, shows that the proposed approach is a viable option for monitoring the respiration frequency and for a rough classification of breathing types. The obtained results were evaluated on a wireless prototype of a respiration body sensor. We indicate the best positions for the respiration body sensor and prove that a single sensor for body surface potential difference on proximal skin electrodes can be used for combined measurements of respiratory and cardiac activities.
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We sought to quantify the fractal scaling properties of human respiratory dynamics and determine whether they are altered with healthy aging and gender. Continuous respiratory datasets (obtained by inductive plethysmography) were collected from 40 healthy adults (10 young men, 10 young women, 10 elderly men, and 10 elderly women) during 120 min of spontaneous breathing. The interbreath interval (IBI) time series were extracted by a new algorithm and fractal scaling exponents that quantify power-law correlations were computed using detrended fluctuation analysis. Under supine, resting, and spontaneous breathing conditions, both healthy young and elderly subjects had scaling exponents for the IBI time series that indicate long-range (fractal) correlations across multiple time scales. Furthermore, the scaling exponents (mean ± SD) for the IBI time series were significantly (p < 0.03) lower (indicating decreased correlations) in the healthy elderly male 0.60 ± 0.08) compared to the young male (0.68 ± 0.07), young female (0.70 ± 0.07), and elderly female (0.67 ± 0.06) subjects. These results provide evidence for fractal organization in physiologic human breathing cycle dynamics, and for their degradation in elderly men. These findings may have implications for modeling integrated respiratory control mechanisms, quantifying their changes in aging or disease, and assessing the outcome of interventions aimed toward restoring normal physiologic respiratory dynamics. © 2002 Biomedical Engineering Society. PAC2002: 8719Uv, 8710+e, 0545Df
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• The level of documentation of vital signs in many hospitals is extremely poor, and respiratory rate, in particular, is often not recorded. • There is substantial evidence that an abnormal respiratory rate is a predictor of potentially serious clinical events. • Nurses and doctors need to be more aware of the importance of an abnormal respiratory rate as a marker of serious illness. • Hospital systems that encourage appropriate responses to an elevated respiratory rate and other abnormal vital signs can be rapidly implemented. Such systems help to raise and sustain awareness of the importance of vital signs.
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Flexible ammonia (NH3) sensors based on one-dimensional nanostructures have attracted great attention due to their high flexibility and low-power consumption. However, it is still challenging to reliably and cost-effectively fabricate ordered nanostructure-based flexible sensors. Herein, a smartphone-enabled fully integrated system based on a flexible nanowire sensor was developed for real-time NH3 monitoring. Highly aligned, sub-100 nm nanowires on a flexible substrate fabricated by facile and low-cost soft lithography were used as sensitive elements to produce impedance response. The detection signals were sent to a smartphone and displayed on the screen in real time. This nanowire-based sensor exhibited robust flexibility and mechanical durability. Moreover, the integrated NH3 sensing system presented enhanced performance with a detection limit of 100 ppb, as well as high selectivity and reproducibility. The power consumption of the flexible nanowire sensor was as low as 3 μW. By using this system, measurements were carried out to obtain reliable information about the spoilage of foods. This smartphone-enabled integrated system based on a flexible nanowire sensor provided a portable and efficient way to detect NH3 in daily life.
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Respiration monitoring is important for evaluating human health. Humidity sensing is a promising way to establish a relationship between human respiration and electrical signal. This work describes polymer humidity sensors with ultrafast response for respiration monitoring. The humidity-sensitive polyelectrolyte is in situ crosslinked on the substrate printed with interdigitated electrodes by a thiol-ene click reaction. The polyelectrolyte humidity sensor owns rapid water adsorption/desorption ability, excellent stability and repeatability. The sensor with ultrafast response and recovery (0.29 s/0.47 s) when changing humidity between 33% and 95% shows good application prospects in breath monitoring and touchless sensing. Different respiration patterns can be distinguished and the breath rate/depth of detection subjects can also be determined by the sensor. In addition, the obtained sensor can sense the skin evaporation by a non-contact way.
Article
This paper investigates the issues on acoustic energy reflection of flexible film bulk acoustic resonators (FBARs). The flexible FBAR was fabricated with an air cavity in the polymer substrate, which endowed the resonator with efficient acoustic reflection and high electrical performance. The acoustic wave propagation and reflection in FBAR were first analyzed by Mason model, and then flexible FBARs of 2.66 GHz series resonance in different configurations were fabricated. To validate efficient acoustic reflection of flexible resonators, FBARs were transferred onto different polymer substrates without air cavities. Experimental results indicate that efficient acoustic reflection can be efficiently predicted by Mason model. Flexible FBARs with air cavities exhibit a higher figure of merit (FOM). Our demonstration provides a feasible solution to flexible MEMS devices with highly efficient acoustic reflection (i.e. energy preserving) and free-moving cavities, achieving both high flexibility and high electrical performance © 2018, Editorial Office of Nanotechnology and Precision Engineering. All right reserved.
Article
Respiration is as one of the most essential physiological signals, which can be used to monitor human healthcare and activities. Herein, we report a flexible, lightweight and highly conductive porous graphene network as the humidity sensor for respiration monitoring. To enhance the sensing performance, the graphene oxide (GO), poly (3, 4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) and Ag colloids (AC) were used to modify the porous graphene. The humidity properties of porous based graphene networks have been investigated at different relative humidity (RH). The porous based graphene sensors exhibit excellent capability of monitoring different breathing patterns including mouse and nose respiration, normal and deep respiration. Besides, the signal variations before and after water intake was recorded by the sensor, which demonstrates the ability to monitor water loss during breathing period. Furthermore, the humidity sensor shows the ability to detect physiological activities including skin moisture, speaking and whistle rhythm, which could be a promising electronic for clinical respiration monitoring.
Article
The pressure sensors should have an excellent sensitivity in the range of 0-20kPa when applied in wearable applications. Traditional pressure sensors can’t achieve both a high sensitivity and a large working range simultaneously, which results to their limited applications in wearable fields. There is an urgent need to develop a pressure sensor to make a breakthrough in both sensitivity and working range. In this paper, a graphene-paper pressure sensor which shows excellent performance in the range of 0-20kPa is proposed. Comparing to most reported graphene pressure sensors, this work realizes the optimization of sensitivity and working range, which is especially suitable for wearable applications. We also demonstrate that the pressure sensor can be applied in pulse detection, respiratory detection, voice recognition as well as various intense motion detections. This graphene-paper pressure sensor will have great potentials in the smart wearable devices to achieve health monitoring and motion detecting.
Article
Real-time monitoring of breath can provide clinically relevant information about apnea syndrome and other important aspects of human physiology. Here, we introduce a flexible skin-like breath sensor developed by transfer-printing vanadium dioxide (VO2) thin films on PDMS substrates. This flexible breath sensor can conformably laminate on the skin under the nose with different curvatures and operate at different environment temperatures through day and night. Attributed to the high temperature coefficient of resistance of VO2, the enhanced breath sensing performance was demonstrated and the response time and recovery time can be as fast as 0.5 s. The excellent sensing performance and fast response time indicate that the VO2-based breath sensor is feasible in monitoring breath for prevention of apnea syndrome.
Article
We developed a highly sensitive humidity sensor based on the combination of ultrahigh-frequency film bulk acoustic resonator (FBAR) and nano-assembled polyelectrolyte (PET) thin films. The water molecule absorption efficiency was optimized by forming loosely-packed PET nanostructures. Then, the humidity sensing characteristics were analyzed in terms of sensitivity, linearity, reversibility, stability and detection limit. As a result, PET-coated FBAR exhibits excellent humidity sensitivity of 2202.20 Hz/ppm, which is five orders of magnitude higher than quartz crystal microbalance (QCM). Additionally, temperature dependence was investigated with the result that PET-coated FBAR possessed a higher sensitivity at low temperature. Furthermore, we realized the selective detection of water vapor from volatile organic compounds (VOCs) with respect to the polarity property. Owing to the high sensitivity, miniaturized size and ultrahigh operating frequency, PET-coated FBAR is uniquely favorable as a wireless humidity sensor node to integrate into wireless sensor networks (WSNs).
Article
We demonstrate a flexible strain-gauge sensor and its use in a wearable application for heart rate detection. This polymer-based strain-gauge sensor was fabricated using a double-sided fabrication method with polymer and metal, i.e., polyimide and nickel-chrome. The fabrication process for this strain-gauge sensor is compatible with the conventional flexible printed circuit board (FPCB) processes facilitating its commercialization. The fabricated sensor showed a linear relation for an applied normal force of more than 930 kPa, with a minimum detectable force of 6.25 Pa. This sensor can also linearly detect a bending radius from 5 mm to 100 mm. It is a thin, flexible, compact, and inexpensive (for mass production) heart rate detection sensor that is highly sensitive compared to the established optical photoplethysmography (PPG) sensors. It can detect not only the timing of heart pulsation, but also the amplitude or shape of the pulse signal. The proposed strain-gauge sensor can be applicable to various applications for smart devices requiring heartbeat detection.
Article
Respiration pattern (including both breath rate and intensity) is critical vital symptoms of many disorders such as sleep apnea, asthma, chronic obstructive pulmonary disease, and anemia. Breath sensors that can distinguish abnormalities in breath patterns can ascertain the basic human body conditions during sleep, exercise, sports and surgery play a significant role in healthcare system and have attracted more and more attentions. However, the existing breath sensors are limited in the sensitivity and not compatible with the practical applications during movements. Here we present a simple approach employing the wrinkled nitrile rubber films to detect the human respiration, both breath rate and intensity The three-dimensional wrinkled structure of nitrile rubber films could significantly increase the capability to distinguish different intensities of respiration, with an average intensity ratio of 16 times for strong breath over weak breath signal These sensors also show fast response (up to 2 Hz) high sensitivity, and can be stretched by 100% with stable breath sensing property. Our respiration sensors are favorable to the urgent healthcare monitoring applications in the near future.
Article
The fabrication of highly responsive, rapid response/recovery and durable relative humidity (%RH) sensors that can precisely monitor humidity levels still remains a considerable challenge for realizing the next generation humidity sensing applications. Herein, we report a remarkably sensitive and rapid %RH sensor having a reversible response using a nanocasting route for synthesizing mesoporous g-CN (commonly known as g-C3N4). The 3D replicated cubic mesostructure provides a high surface area thereby increasing the adsorption, transmission of charge carriers and desorption of water molecules across the sensor surfaces. Owing to its unique structure, the mesoporous g-CN functionalized with well dispersed catalytic Ag nanoparticles exhibits excellent sensitivity in the 11-98% RH range while retaining high stability, negligible hysteresis and superior real time %RH detection performances. Compared to conventional resistive sensors based on metal oxides, a rapid response time (3 s) and recovery time (1.4 s) were observed in the 11-98% RH range. Such impressive features originate from the planar morphology of g-CN as well as unique physical affinity and favourable electronic band positions of this material that facilitate water adsorption and charge transportation. Mesoporous g-CN with Ag nanoparticles is demonstrated to provide an effective strategy in designing high performance %RH sensors and show great promise for utilization of mesoporous 2D layered materials in the Internet of Things and next generation humidity sensing applications.
Article
A room temperature multimodal sensor composed of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) deposited on an AT-cut quartz crystal microbalance (QCM) crystal was fabricated. The sensor’s nonlinear motional resistance and frequency responses are deconvoluted using a feedforward backpropagation neural network (FBN), which allows a single sensor to function simultaneously as a relative humidity (RH) sensor and a pressure sensor using only two electrodes. We demonstrate that the predictive ability of the sensor is highly influenced by the data used to train the FBN. When training sets are tailored to resemble the operating conditions of the sensor, the sensor achieves an average resolution of <4% RH from 0-100% RH, even after H2O saturation occurs on the surface. Our results indicate that FBNs show strong promise for improving the resolution of low cost gas sensors and for expanding the range of environmental conditions in which a given sensor can operate.
Article
Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.
Article
Flexible and stretchable physical sensors that can measure and quantify electrical signals generated by human activities are attracting a great deal of attention as they have unique characteristics, such as ultrathinness, low modulus, light weight, high flexibility, and stretchability. These flexible and stretchable physical sensors conformally attached on the surface of organs or skin can provide a new opportunity for human-activity monitoring and personal healthcare. Consequently, in recent years there has been considerable research effort devoted to the development of flexible and stretchable physical sensors to fulfill the requirements of future technology, and much progress has been achieved. Here, the most recent developments of flexible and stretchable physical sensors are described, including temperature, pressure, and strain sensors, and flexible and stretchable sensor-integrated platforms. The latest successful examples of flexible and stretchable physical sensors for the detection of temperature, pressure, and strain, as well as their novel structures, technological innovations, and challenges, are reviewed first. In the next section, recent progress regarding sensor-integrated wearable platforms is overviewed in detail. Some of the latest achievements regarding self-powered sensor-integrated wearable platform technologies are also reviewed. Further research direction and challenges are also proposed to develop a fully sensor-integrated wearable platform for monitoring human activity and personal healthcare in the near future.
Article
Noninvasive and real-time cuffless blood pressure (BP) measurement realizes the idea of unobtrusive and continuous BP monitoring which is essential for diagnosis and prevention of cardiovascular diseases associated with hypertension. In this paper, a wearable sensor patch system that integrates flexible piezoresistive sensor (FPS) and epidermal electrocardiogram (ECG) sensors for cuffless BP measurement is presented. By developing parametric models on the FPS sensing mechanism and optimizing operational conditions, a highly stable epidermal pulse monitoring method is established and beat-to-beat BP measurement from the ECG and epidermal pulse signals is demonstrated. In particular, this study highlights the compromise between sensor sensitivity and signal stability. As compared with the current optical-based cuffless BP measurement devices, the sensing patch requires much lower power consumption (3 nW) and is capable of detecting subtle physiological signal variations, e.g., pre and postexercises, thus providing a promising solution for low-power, real-time, and home-based BP monitoring.
Article
On page 119, J. A. Rogers and co-workers present theoretical approaches, modeling algorithms, materials, and device designs for the noninvasive measurement of core body temperature by using multiple differential temperature sensors that attach softly and intimately onto the surface of the skin. The image shows the construction of differential temperature sensors using thermally insulating foam as the separation material.
Article
A novel Ni nanofoam electrode has been fabricated by low-cost methods and applied for non-enzymatic glucose sensing. Ni(OH)2 nanowalls, prepared by room-temperature chemical bath deposition, were transformed into an ensemble of Ni nanoparticles (20-30 nm in size) upon annealing in forming gas at 350 °C, and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), temperature programmed reduction with hydrogen (H2-TPR) and surface area measurements. The Ni nanofoam was converted to the catalytic Ni(OH)2/NiOOH - necessary for non-enzymatic glucose oxidation - by cyclic voltammetry (CV) in NaOH electrolyte. The electrode fabricated on conducting glass substrate showed a glucose sensitivity of 2.37 mA/cm2 mM, a linear range of 0.01-0.7 mM, a limit of detection (LOD) of 5 μM, a fast response time (1 s), and resistance to chloride poisoning. The glucose sensor also exhibited an excellent long-term stability (4% decrease in sensitivity after 64 days) and selectivity in the presence of common interfering species. The versatility of the preparation method was demonstrated in the fabrication of a flexible (plastic substrate) sensor with a sensitivity of 1.43 mA/cm2 mM. The ease of fabrication and the excellent properties of Ni nanofoam in glucose sensing make it promising for low-cost and wearable sensing applications.
Article
Despite the ubiquity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a transparent conducting electrode in flexible organic electronic devices, its potential as a stretchable conductor has not been fully explored. This paper describes the electronic and morphological characteristics of PEDOT:PSS on stretchable poly(dimethylsiloxane) (PDMS) substrates. The evolution of resistance with strain depends dramatically on the methods used to coat the hydrophobic surface of PDMS with PEDOT:PSS, which is cast from an aqueous suspension. Treatment of the PDMS with an oxygen plasma produces a brittle skin that causes the PEDOT:PSS film to fracture and an increase in resistivity by four orders of magnitude at only 10% strain. In contrast, a mild treatment of the PDMS surface with ultraviolet/ozone (UV/O3) and the addition of 1% Zonyl fluorosurfactant to the PEDOT:PSS solution produces a mechanically resilient film whose resistance increases by a factor of only two at 50% strain and retains significant conductivity up to 188% strain. Examination of the strained surfaces of these resilient PEDOT:PSS films suggests alignment of the grains in the direction of strain. Wave-like buckles that form after the first stretch >10% render the film reversibly stretchable. Significant cracking (2 cracks mm–1) occurs at 30% uniaxial strain, beyond which the films are not reversibly stretchable. Cyclic loading (up to 1000 stretches) produces an increase in resistivity whose net increase in resistance increases with the value of the peak strain. As an application, these stretchable, conductive films are used as electrodes in transparent, capacitive pressure sensors for mechanically compliant optoelectronic devices.
Article
The development of wearable electronics which can monitor the human physiological information demands specially structured materials with excellent stretchability and electrical conductivity. In this study, a new stretchable conductive polypyrrole (PPy)/polyurethane (PU) elastomer was designed and prepared by surface diffusion and in situ polymerization of PPy in- and onside porous PU substrates. The structures allowed the formation of net-like micro-cracks under stretching. The net-like micro-crack structures make it possible that the reversible changes in the electrical resistance of PPy/PU elastomers under stretching and releasing cycles. The variations in morphology and chemical structures, stretchability, conductivity, as well as the sensitivity of resistance change under stretching cycles were investigated. The mechanism of reversible conductivity of the PPy/PU elastomer was proposed. This property was then used to construct a waistband-like human breath detector. The results demonstrated its potential as strain sensor for human health care applications, by showing reversible resistance changes in the repeated stretching and contracting motion when human breath in and out.
Article
The nanometer-size crystallization of poly(3,4-ethylenedioxythiophene) (PEDOT) inside the hydrophobic core region of PEDOT:PSS (PSS: poly(4-styrenesulfonate)) in a solid film is found by small and wide-angle X-ray scatterings using a synchrotron radiation source. The clarified PEDOT:PSS structure indicates that a nanocrystal of PEDOT surrounded by PSS is grown in the solid film from randomly oriented PEDOT in a micelle dispersed in water during the course of film fabrication. The addition of ethylene glycol (EG) to the PEDOT:PSS water dispersion and post-treatment of the pristine film with EG both provide similar improvements in PEDOT crystallinity. The crystallite size of PEDOT increases up to a comparable size (4.8 nm) to the hydrophobic PEDOT core region of the micelle. The electrical conductivity of the solid film is concurrently enhanced by 2 orders of magnitude with the growing nanocrystal of PEDOT. These findings clearly demonstrate the importance of the single crystalline PEDOT assisted by EG to obtain high electrical conductivity of the PEDOT:PSS solid film.
Article
Precision thermometry of the skin can, together with other measurements, provide clinically relevant information about cardiovascular health, cognitive state, malignancy and many other important aspects of human physiology. Here, we introduce an ultrathin, compliant skin-like sensor/actuator technology that can pliably laminate onto the epidermis to provide continuous, accurate thermal characterizations that are unavailable with other methods. Examples include non-invasive spatial mapping of skin temperature with millikelvin precision, and simultaneous quantitative assessment of tissue thermal conductivity. Such devices can also be implemented in ways that reveal the time-dynamic influence of blood flow and perfusion on these properties. Experimental and theoretical studies establish the underlying principles of operation, and define engineering guidelines for device design. Evaluation of subtle variations in skin temperature associated with mental activity, physical stimulation and vasoconstriction/dilation along with accurate determination of skin hydration through measurements of thermal conductivity represent some important operational examples.
Article
In this study, a new simple, fast, and inexpensive technique for the preparation of free-standing nanocomposite ultrathin films based on the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and embedding iron oxide nanoparticles (NPs) is presented. These nanofilms were fabricated by a single step of spin-coated assisted deposition in conjunction with a release technique ("supporting layer technique") to detach them from the substrate. Free-standing nanofilms can be easily transferred onto several substrates due to their high conformability, preserving their functionalities. The effect of the addition of iron oxide nanoparticles on the structural and functional properties of the PEDOT:PSS nanofilms is investigated through topography, thickness, magnetic, magneto-optical activity, and conductivity characterizations. PEDOT:PSS and PEDOT:PSS/iron oxide NP nanofilms were tested as resistive humidity sensors. Their sensitivity to humidity was found to increase with increasing nanoparticle concentration. On the basis of these results, it is expected that these composites may furnish inexpensive and reliable means for relative humidity detection.
Article
PEDOT:PSS humidity sensor was fabricated using a drop-casting method between thermally evaporated gold electrodes with 30 μm separation and 300 μm channel width on a glass substrate. AC, DC resistivity, and AFM techniques were used to characterize the PEDOT:PSS humidity sensor in the same environmental conditions. The change of resistivity was monitored with increasing relative humidity (RH) up to 90%. The resistivity increases linearly up to a maximum value, and then it starts to decrease abruptly above 80% relative humidity (RH) after saturation of water uptake. The decrease in resistivity above 80% RH seems to be due to the water meniscus layer formed on the saturated PEDOT:PSS film. Below 80% RH, the device works like a humidity sensor.
Article
Respiration monitoring in everyday life enables the early detection of the diseases and disorders that can suddenly manifest in a life threatening episode. Long-term monitoring can extend the capabilities of healthcare providers if reliability can be achieved economically. In this paper, the potential for using capacitive sensing to serve as an inexpensive method for long-term respiration sensing is explored. This paper proposes new designs of capacitive sensors for respiration sensing and describes the design and fabrication of a prototype textile-based capacitive-sensor respiration belt. Two capacitive sensors were designed and fabricated for detecting chest or abdominal circumference changes of up to 60 mm. These sensors gave good linearity, and the respiration measurements obtained with these new sensors show that they are capable of measuring respiration rate, and possibly lung function parameters.
Article
A new compressible conducting material has been developed by coating polyurethane (PU) foam with inherently conducting polypyrrole (PPy). The optimised conditions for preparation of the conducting foam have been investigated. Evaluation of the conducting foam shows that a linear relationship exists between the conductance and the stress applied. Parameters such as sensitivity, dynamic range, repeatability of this pressure sensor are discussed. The use of this soft pressure sensor in a prototype breath monitor is also reported.
Article
Within the past years there has been much effort in developing and improving new techniques for the nanoscale patterning of functional materials used in promising applications like nano(opto)electronics. Here a high-resolution soft lithography technique—nanomolding in capillaries (NAMIC)—is demonstrated. Composite PDMS stamps with sub-100 nm features are fabricated by nanoimprint lithography to yield nanomolds for NAMIC. NAMIC is used to pattern different functional materials such as fluorescent dyes, proteins, nanoparticles, thermoplastic polymers, and conductive polymers at the nanometer scale over large areas. These results show that NAMIC is a simple, versatile, low-cost, and high-throughput nanopatterning tool.
Article
Vital sign measurements, specifically heart rate, respiratory rate, and blood pressure, play a fundamental role in many medical evaluations, yet little is known about the reliability of noninvasive vital sign measurements. We sought to determine whether trained observers can reproducibly assess vital signs in the clinical setting. Two trained observers independently measured vital signs on 140 patients presenting to an urban emergency department with acute medical complaints. Heart rate and respiratory rate were each measured by auscultation of heart and breath sounds for 1 minute. Systolic and diastolic blood pressures were determined by auscultating Korotkoff sounds while viewing pressure measurements from a standard cuff and mercury manometer. The mean value of each vital sign and Bland-Altman statistics (mean difference between observers [MDO], expected range of agreement [ERA]) were used to provide absolute and relative indices of reliability. The observers found a mean heart rate of 78.5 beats/min, with an MDO of 0.02 beats/min (0.03%), and an ERA of +/- 10.6 beats/min (+/- 13.5%). Respiratory rate exhibited a mean of 17.5 breaths/min, an MDO of 0.04 breaths/min (0.2%), and an ERA of +/- 6.2 breaths/min (+/- 35.5%). The mean systolic blood pressure of 127.1 mm Hg was associated with an MDO of 1.3 mm Hg (1.0%), and an ERA of +/- 24.2 mm Hg (+/- 19.0%). Diastolic blood pressure exhibited a mean of 77.4 mm Hg, an MDO of 0.3 mm Hg (0.4%) with an ERA of +/- 19.9 mm Hg (+/- 25.7%). The reproducibility of vital sign measurements may be limited by significant interobserver variability. Clinicians should recognize this inherent variability and interpret vital signs with caution.
Article
Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) is a form of periodic breathing, commonly observed in patients with heart failure (HF), in which central apneas alternate with hyperpneas that have a waxing-waning pattern of tidal volume. Uniform criteria by which to diagnose a clinically significant degree of CSR-CSA have yet to be established. CSR-CSA is caused by respiratory control system instability characterized by a tendency to hyperventilate. Central apnea occurs when Pa(CO(2)) falls below the threshold for apnea during sleep due to ventilatory overshoot. Patients with CSR-CSA are generally hypocapnic, with a Pa(CO(2)) closer than normal to the apneic threshold such that even slight augmentation in ventilation drives Pa(CO(2)) below threshold and triggers apnea. Factors contributing to hyperventilation in HF include stimulation of pulmonary irritant receptors by pulmonary congestion, increased chemoreceptor sensitivity, reduced cerebrovascular blood flow, and recurrent arousals from sleep. Controversy remains as to whether CSR-CSA is simply a reflection of HF severity, or whether it exerts unique adverse effects on prognosis. The main adverse influence of CSR-CSA on cardiovascular function appears to be excessive sympathetic nervous system activity due to apnea-related hypoxia and arousals from sleep. A number of studies have examined the potential relationship between CSR-CSA and mortality in HF. Most reported that CSR-CSA was associated with an increased risk for mortality, but these studies were small. Further research is therefore needed to elucidate mechanisms which contribute to the pathogenesis of CSR-CSA, and to determine whether its treatment can reduce morbidity and mortality in patients with HF.
Conference Paper
A new system for non-contacting respiratory air flow detection is presented. Airborne ultrasound is being used to detect variations in the velocity of sound caused by air flow. Two opposing ultrasonic waves are reflected by the face of the subject to be investigated, and variations in the differential transit times, or phase shifts, are recorded. Due to the non-reciprocity of flow, it is possible to obtain specificity against other influences, such as movements of the subject. Experimentally, an operating frequency in the range 40-200 kHz has been found feasible. In the prototype system, continuous waves emitted by standard piezoelectric transducers operating at 40 kHz and of slightly different frequencies are used for identification of the opposing waves. A linear flow dependence has been verified, with adequate resolution. The function has also been verified on human subjects. A wide range of high-priority clinical applications can be foreseen for the system.