Article

Chemiresistive Sensor Array from Conductive Polymer Nanowires Fabricated by Nanoscale Soft Lithography

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Abstract

One-dimensional organic nanostructures are essential building blocks for high performance gas sensors. Constucting as e-nose type sensor array is the current golden standard in develping portable system for gas mixtures detection. However, facile fabrication of nanoscale sensor array is still challenging due to the high cost of the conventional nanofabication techniques. In this work, we fabricate chemiresistive gas sensor array composed of well-ordered sub-100 nm wide conducting polymer nanowires using cost-effective nanoscale soft lithography. The poly (3,4-ethylene-dioxythiophene)-poly (styrene sulfonate) (PEDOT: PSS) nanowires functionalized by different self-assembled monolayers (SAMs) are capable of identifying volatile organic compounds (VOCs) at low concentrations range. The side chains and functional groups of the SAMs introduce different sensitivity and selectivity to the targeted analytes. The distinct response pattern of each chemical is subjected to pattern recognition protocols, which leads to a clear separation towards ten VOCs, including ketones, alcohols, alkanes, aromatics and amines. These results of the chemiresistive gas sensor array demonstrate that the nanoscale soft lithography is a reliable approach for fabricating nanosclae devices and have the potential of mass producibility.

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... First, the inexhaustible abundance of hybrid materials (in both the complex constituents and novel nanostructures) makes it possible to involve an almost infinite continuum of variable factors (surface-dependent factor, interfacedependent factor, and structure-dependent factor) to generate new sensing behaviors (Fig. 1c) [38][39][40][41][42][43][44][45][46][47][48][49]. Second, with hybrid material, more chemical/physical processes with different enhanced mechanisms could be introduced to precisely design, regulate, and enhance the sensing performance mainly through catalytic reaction with analyte [50][51][52][53][54][55][56][57][58], charge transfer [59][60][61][62][63], charge carrier transport [64][65][66] manipulation/construction of heterojunctions [39, 1 3 67], molecular binding/sieving [68][69][70][71][72][73], and their combinations [74][75][76][77]. ...
... The fourth relies on manipulation/construction of the heterojunctions such as n-n, p-n, p-p, p-n-p heterogeneous semi-conductive materials (categorized as interface-dependent factor) [39]. The last one relies on semiconductors coated by gas molecular sieving/ binding layers or ligands/complexes for selective gas detection (categorized as surface-and structure-dependent factor) [72,76,82]. In the following section, we provide more details on each of these combinations. ...
... The existence of SAM on the surface of inorganic materials (except 2D nanomaterials) limits the working temperature, which greatly weakens the sensing performance, although it could be resolved by UV irradiation. Using conductive polymer as the host material with surface SAM functionalization by the "1-stone 2 birds" strategy was promising and novel (Fig. 15d, e) [72]. Superb sensing performances were achieved by combining RT sensitivity of CP and good selectivity of SAM (Fig. 15f) [72]. ...
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Chemi-resistive sensors based on hybrid functional materials are promising candidates for gas sensing with high responsivity, good selectivity, fast response/recovery, great stability/repeatability, room-working temperature, low cost, and easy-to-fabricate, for versatile applications. This progress report reviews the advantages and advances of these sensing structures compared with the single constituent, according to five main sensing forms: manipulating/constructing heterojunctions, catalytic reaction, charge transfer, charge carrier transport, molecular binding/sieving, and their combinations. Promises and challenges of the advances of each form are presented and discussed. Critical thinking and ideas regarding the orientation of the development of hybrid material-based gas sensor in the future are discussed.
... Moreover, in recent years, 1D-or 2D-CP nanostructures have proven to increase the performance of this type of gas sensors. In [132], for instance, CP nanowires (<100 nm) are deployed as the active layer in a chemiresistive sensor array, using a cost-effective nanoscale soft lithography. The fabricated sensors show pretty high sensitivities upon exposure to different VOCs between 150 and 2000 ppm and LOD below 50 ppm. ...
... Besides, recent studies show other OSCs in the form of nanocomposites with even higher sensitivities, detection limits in the ppb range (e.g., 100 ppb), and also fast responses (e.g., 3-7 s) [144]. In conclusion, one of the main advantages of polymeric materials (i.e., CP, IP, and OSCs) is that they can be easily miniaturized into micro-or nanostructures, by employing new micromachining techniques, such as electrochemical deposition [139], drop casting, screen printing [145], soft lithography [132], micromolding [135], dip-or spin coating [96], which have enabled to deploy micro-and nanofilms onto target substrates. Owing to high surface-to-volume ratios, these micro-and nanopolymeric films offer a better interaction with target analytes, which contribute to high sensitivities and performances of gas sensing devices. ...
... Sensors 2020, 20, x FOR PEER REVIEW 12 of 41 lithography [132], micromolding [135], dip-or spin coating [96], which have enabled to deploy microand nanofilms onto target substrates. Owing to high surface-to-volume ratios, these micro-and nanopolymeric films offer a better interaction with target analytes, which contribute to high sensitivities and performances of gas sensing devices. ...
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In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans' olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoring.
... However, studying and applying liquid metal-based flexible and wearable sensors within the context of microfluidics is a relatively new field of research and is evolving very quickly [26][27][28]. Thus, taking advantage of microfluidics technology or structures for patterning and embedding the liquid metal, a design of flexible and wearable sensors is utilized in this study for the development of a functional human-machine interface [29][30][31]. 2 of 14 In the present paper, a long service life, wearable functional human-machine interface with integrated electrode sensors is developed [32], as shown in Figure 1a. We embed conductive eutectic gallium indium alloy and PDMS as materials featured with injecting the micron−scale microchannels [33][34][35]. ...
... The results demonstrate the multifunctional sensing abilities of the developed liquid metal−based sensor and verify its potential in wearable applications as an interaction interface between humans and machines. ding the liquid metal, a design of flexible and wearable sensors is utilized in this study for the development of a functional human-machine interface [29][30][31]. ...
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Rigid sensors are a mature type of sensor, but their poor deformation and flexibility limit their application range. The appearance and development of flexible sensors provide an opportunity to solve this problem. In this paper, a resistive flexible sensor utilizes gallium−based liquid metal (eutectic gallium indium alloy, EGaIn) and poly(dimethylsiloxane) (PDMS) and is fabricated using an injecting thin−line patterning technique based on soft lithography. Combining the scalable fabrication process and unique wire−shaped liquid metal design enables sensitive multifunctional measurement under stretching and bending loads. Furthermore, the flexible sensor is combined with the glove to demonstrate the application of the wearable sensor glove in the detection of finger joint angle and gesture control, which offers the ability of integration and multifunctional sensing of all−soft wearable physical microsystems for human–machine interfaces. It shows its application potential in medical rehabilitation, intelligent control, and so on.
... The rGO-based sensors generally have better response than graphene-based ones because defects remain in chemical GO after removing a large number of oxygen-containing functional groups; i.e., water and -COOH groups are removed (Figure 4), which enhances the ability of rGO to adsorb gas molecules [55]. The sensor curves exhibit different slopes, pointing to cross-validation based on an array for single VOC recognition and enhances qualitative accuracy [56]. ...
... For example, the blue dot on the left side of Figure 8a is obtained at the lowest ethanol. When the first two principal components (PC) are considered, the cumulative contribution reaches 95.5%, which means that the most information can be reasonably described [56]. Overall, the five VOCs can be distinguished. ...
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We investigated functionalized graphene materials to create highly sensitive sensors for volatile organic compounds (VOCs) such as formaldehyde, methanol, ethanol, acetone, and isopropanol. First, we prepared VOC-sensitive films consisting of mechanically exfoliated graphene (eG) and chemical graphene oxide (GO), which have different concentrations of structural defects. We deposited the films on silver interdigitated electrodes on Kapton substrate and submitted them to thermal treatment. Next, we measured the sensitive properties of the resulting sensors towards specific VOCs by impedance spectroscopy. We obtained the eG- and GO-based electronic nose composed of two eG films- and four GO film-based sensors with variable sensitivity to individual VOCs. The smallest relative change in impedance was 5% for the sensor based on eG film annealed at 180 °C toward 10 ppm formaldehyde, whereas the highest relative change was 257% for the sensor based on two-layers deposited GO film annealed at 200 °C toward 80 ppm ethanol. At 10 ppm VOC, the GO film-based sensors were sensitive enough to distinguish between individual VOCs, which implied excellent selectivity, as confirmed by Principle Component Analysis (PCA). According to a PCA-Support Vector Machine-based signal processing method, the electronic nose provided identification accuracy of 100% for individual VOCs. The proposed electronic nose can be used to detect multiple VOCs selectively because each sensor is sensitive to VOCs and has significant cross-selectivity to others.
... In recent years, researchers have devoted themselves to the development of various nanomaterials and their manufacturing methods, which have opened up new research directions for nano-biotechnology in the field of biomedicine. Due to its special optical and physical properties, quantum dots (QDs) have caught the attention of various research fields (Alivisatos, 1996;Dabbousi et al., 1997;Niemeyer, 2001;Fu and Lakowicz, 2006;Jiang et al., 2018;Tang et al., 2019;Wang et al., 2019). Quantum dots can be used as fluorescent markers to detect proteins, DNA, and specific proteases qualitatively or quantitatively. ...
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In recent years, non-toxic quantum dot has caught the attention of biomedical fields. However, the inherent cytotoxicity of QDs makes its biomedical application painful, and is a major drawback of this method. In this paper, a non-toxic and water-soluble quantum dot AgInZnS-GO using graphene oxide was synthesized. A simple model of state complex was also established, which is produced through a combination of quantum dots and protein. The interaction between AIZS-GO QDs and human serum albumin (HSA) has significant meaning in vivo biological application. Herein, the binding of AIZS-GO QDs and HSA were researched using fluorescence spectra, Uv-visible absorption spectra, FT-IR spectra, and circular dichroism (CD) spectra. The results of fluorescence spectra demonstrate that AIZS-GO QDs have an obvious fluorescence quenching effect on HSA. The quenching mechanism is static quenching, which implies that some type of complex was produced by the binding of QDs and HSA. These results were further proved by Uv-visible absorption spectroscopy. The Stern-Volmer quenching constant Ksv at various temperatures (298 K, 303 K, 308 K) were acquired from analyzing Stern-Volmer plots of the fluorescence quenching information. The Van't Hoff equation could describe the thermodynamic parameters, which demonstrated that the van der Waals and hydrogen bonds had an essential effect on the interaction. FT-IR spectra and CD spectra further indicate that AIZS-GO QDs can alter the structure of HSA. These spectral methods show that the quantum dot can combine well with HSA. The experimental results showed that AgInZn-GO water-soluble quantum dots have good biocompatibility, which can be combined with proteins to form new compounds which have no cytotoxicity and biological practicability. It provides an important basis for the combination of quantum dots and specific proteins as well as fluorescent labeling.
... Conducting polymer-based composite material and nanoparticlebased composite materials are generally used to fabricate electrochemical biosensors due to their conductivity, low resistance, biocompatibility and, high mechanical and chemical strengths. Various procedures such as soft/photolithography, chemical, and enzymatic methods have been proposed to fabricate a conducting polymer-based sensor matrix [59][60][61]. Generally, lithographic methods require high energy, and this high-energy environment does not allow the doping of biomolecules with conductive polymers. ...
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Recent developments in the biochemical and medicinal industries have been heavily focused on producing affordable glucose biosensors due to the continuous annual increase of diabetic patients worldwide. The development of a fast, accurate, and reliable glucose sensor will increase confidence in controlling diabetes mellitus and its associated health complications among the diabetic community. Electrospinning is a versatile method that can produce complex nanofibrous assemblies with attractive and functional characteristics from various polymers. Electrospun nanofibers demonstrated high efficiency in the immobilization of biological molecules, which can improve the sensing performance further. Integration of polymer electrospun nanofibers with metal nanoparticles, metal oxide or transition metal in producing nanobiocomposites is also a highly popular approach in the past few years. This report presents the current progress and research trends of the technique, focusing on various materials and fabrication strategies used to produce biosensing interfaces. This helps readers decide the suitable approach in designing highly sensitive, selective, fast, and inexpensive glucose sensors.
... In the area of environmental monitoring, sensors for monitoring toxins, pathogens, and heavy metals in water have been reported. The operating principle of a CR/FET sensor is based on the change in electrical resistance that responds to chemical stimuli [1][2][3]. A CR can be regarded as a FET without applying a physical gate voltage and is therefore easier to operate. ...
Article
This study reports the design and development of a novel chemiresistor (CR) sensor using ion imprinted polymer (IIP)-functionalized reduced graphene oxide (rGO) [IIP/rGO-CR] for cadmium ions (Cd(II)) determination in water. The sensor consisted of a CR transducer made of rGO channel bridging source and drain electrodes prepared by self-assembly and thermal reduction of graphene oxide (GO) on Au interdigitated electrodes chip fabricated on Si/SiO2 substrate. The IIP was then grafted on rGO using surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization with polyethylenimine (PEI) and methylacrylic acid (MAA) as dual functional monomers and Cd(II) ions as template through UV light-initiated copolymerization. The IIP functionalized on rGO acted as an effective recognition element that modulated the resistance of rGO-CR upon binding of Cd(II), enabling Cd(II) detection at ppb level in aqueous solutions. The prepared IIP/rGO-CR sensor worked effectively in the linear range of 2~200 ppb and achieved a limit of detection (LOD) of 0.83 ppb, which is lower than the World Health Organization guidelines of 3 ppb for drinking water quality. The developed sensor of IIP/rGO-CR showed a high selectivity against a variety of trace and heavy metal ions found in water and good stability for up to 60 days when stored at room temperature for Cd(II) determination in water. Further, the sensor was successfully applied to analyzing Cd(II) spiked in tap, lake and river waters with a 94.5%–113.5% recovery, demonstrating a high degree of accuracy even in complex water samples. Our results illustrated that the CR sensor of IIP functionalized rGO provides a potential platform for sensitive, robust and low-cost environmental analysis of Cd(II) in water.
... The alignment of nanostructures into three-dimensional states such as nanowires, nanoparticles, nanoribbons, nanorods, and nanosheets were given special attention during gas sensor development. [21][22][23][24][25][26][27][28][29][30] Additionally, large crystal/ grain size and large surface area are the main aspects to improve the sensitivity of the gas sensor. 31 Core shell structure of n-type and p-type combination of metal oxide like n-n, n-p, p-p can lead to synergetic effects that enhance the gas sensitivity leading to an increase in number of publications in this subject area, especially the last decade has witnessed tremendous growth. ...
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Development of highly sensitive, stable and reliable eco-friendly gas sensors is still an open-ended research domain and thus demands many related materials. Bismuth-based compounds form an important material platform in such developments; however, they are so far not reviewed. This review highlights the detailed gas sensing attributes for a range of gases and humidity for n-type and p-type as well as mixed composite materials and influences of catalytic doping on gas sensing in different bismuth-based composites. The future scope in the development of such gas sensors leading to commercialization is also discussed.
... A paper test-strip technology, used in conjunction with a modern hand-held reflectometer was tested to permit fine spatial and temporal resolution analysis of nitrite breakthrough in a large undisturbed soil block. The techniques proved cost effective and had the added benefit of stopping locally generated toxic waste (Holden and Scholefield, 2008;Jiang et al., 2018). However, some of these methods have low accuracy and sensitivity, some of them are time-consuming and require expensive apparatuses which are also operated by highly expert experimenter. ...
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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.
... The developed chemoresistive sensor array is available for a variety of applications and is optimized for the detection of other analyte classes not investigated in this study by optimizing other Jiang et al developed an e-nose chemoresistive sensor with poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) nanowire by nanolithography. 112 Figure 13A shows an optical image of a nanowire chemoresistive sensor with deposited electrodes. As shown in Figure 13A, a conductive channel of 100 μm width is defined by depositing the electrode. ...
Article
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An electronic nose (e‐nose) is a device that can detect and recognize odors and flavors using a sensor array. It has received considerable interest in the past decade because it is required in several areas such as health care, environmental monitoring, industrial applications, automobile, food storage, and military. However, there are still obstacles in developing a portable e‐nose that can be used for a wide variety of applications. For practical applications of an e‐nose, it is necessary to collect a massive amount of data from various sensing materials that can transduce interactions with molecules reliably and analyze them via pattern recognition. In addition, the possibility of miniaturizing the e‐nose and operating it with low power consumption should be considered. Moreover, it should work efficiently over a long period of time. To satisfy these requirements, several different chemoresistive material platforms including metal oxides, organics such as polymers and carbon‐based materials, and two‐dimensional materials were investigated as sensor elements for an e‐nose. As an individual material has limited selectivity, there is a continuing effort to improve the selectivity and gas sensing properties through surface decoration and compositional and structural variations. To produce a reliable e‐nose, which can be used for practical applications, researches in various fields have to be harmonized. This paper reviews the progress of research on e‐noses based on a chemoresistive gas sensor array and discusses the inherent challenges and potential solutions. Oxides, metals, polymers, and 2D materials have emerged as promising materials for the electronic nose. Recent significant developments of the electronic nose are reviewed with a focus on the sensing materials, characteristics, and applications. The future challenges and prospects in developing a semiconductor gas sensor array based electronic nose are discussed.
... With the rapid development of society, deteriorating environmental problems and personal healthcare have been widely concerned. Therefore, effective detection of gases, including volatiles, toxic gases, moisture, and explosives, becomes more and more important in human daily life health and future production [1][2][3][4][5][6][7][8][9][10]. Specifically, in addition to the moisture, there are more than 3000 kinds of volatiles in the samples from human exhaled breath and skin headspace, which provide abundant information about metabolic disorders or dysfunctions of the human body [11][12][13]. ...
Article
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.
... where DR is the maximum difference between responses in the hysteresis cycle measurement at the same concentration and Y is the overall maximum response in this particular cycle. 31 The hysteresis depth in the device was found to be $11.28% as calculated from Fig. 4(c). Furthermore, it was necessary to ascertain the repeatability of the device. ...
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We report on a chemiresistive gas sensor using boron nanostructures as sensing layer,, to detect methane gas down to 50 ppm. The sensor showed an excellent response of 43.5%-153.1% for...
... In this study, height and width of nanowires were also controlled for specific applications of optical gratings and electrodes. Jiang et al [93] also fabricated PEDOT-PSS nanowires using a hybrid stamp with nanochannels, which were synthesized by NIL. The stamp was first attached to the substrate forming parallel nanochannels, which were then filled with the polymer solution by capillary forces. ...
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Advances in nanotechnology in the last decades have paved the way for significant achievements in diagnosis and treatment of various diseases. Different types of functional nanostructures have been explored and utilized as tools for addressing the challenges in detection or treatment of diseases. In particular, one-dimensional nanostructures hold great promise in theranostic applications due to their increased surface area-to-volume ratios, which allow better targeting, increased loading capacity and improved sensitivity to biomolecules. Stable polymeric nanostructures that are stimuli-responsive, biocompatible and biodegradable are especially preferred for bioapplications. In this review, different synthesis techniques of polymeric one-dimensional nanostructures are explored and functionalization methods of these nanostructures for specific applications are explained. Biosensing and drug delibiovery applications of these nanostructures are presented in detail.
... Various types of gas sensors such as electrochemical, optical, acoustic and conductometric, etc., have been explored in gas sensing field [3][4][5][6][7]. Among these sensors, resistive or fieldeffect transistor (FET) sensors are nowadays demanded in this nanotechnology era because of its easy fabrication, possible miniaturization, low cost and simple operation [8][9][10][11][12]. Moreover, different materials such as semiconducting metal oxides, carbon nanotubes (CNTs) and most emerging twodimensional (2D) materials have been employed for developing resistive gas sensors [13][14][15][16]. ...
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Operations of metal oxide semiconductors gas sensors at room temperature under photoactivation are discussed.Emerging two-dimensional (2D) materials-based gas sensors under light illumination are summarized.The advantages and limitations of metal oxides and 2D-materials-based sensors in gas sensing at room temperature under photoactivation are highlighted. Operations of metal oxide semiconductors gas sensors at room temperature under photoactivation are discussed. Emerging two-dimensional (2D) materials-based gas sensors under light illumination are summarized. The advantages and limitations of metal oxides and 2D-materials-based sensors in gas sensing at room temperature under photoactivation are highlighted. Room-temperature gas sensors have aroused great attention in current gas sensor technology because of deemed demand of cheap, low power consumption and portable sensors for rapidly growing Internet of things applications. As an important approach, light illumination has been exploited for room-temperature operation with improving gas sensor’s attributes including sensitivity, speed and selectivity. This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field. First, recent advances in gas sensing of some exciting different nanostructures and hybrids of metal oxide semiconductors under light illumination are highlighted. Later, excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism. Originated impressive features from the interaction of photons with sensing materials are elucidated in the context of modulating sensing characteristics. Finally, the review concludes with key and constructive insights into current and future perspectives in the light-activated nanomaterials for optoelectronic gas sensor applications.
... To fabricate aligned arrays of NWs, various methods such as lithography [44], focused electron beam induced deposition [45], and template-based electrochemical deposition [46,47] can be employed, allowing for the control of the nucleation and growth process. For industrial purposes, the electrochemical method depositing metal ions in nanopores of polycarbonate [48], ion-track etched [49] and anodic aluminum oxide (AAO) [50] templates is preferred over other bottom-up methods due to its cost-effectiveness, simplicity and efficiency. ...
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Realizing promising materials for use in next-generation devices at the nanoscale is of enormous importance from both fundamental and applied perspectives. Nonmagnetic and magnetic metal nanowire (NW) arrays fabricated by template-based electrodeposition techniques have long been considered as good candidates for this purpose. In this review, we focus on the fabrication techniques and characterizations of electrochemically deposited NWs with single, binary, ternary and multilayered component structures mostly carried out in our group. Particular attention is paid to the crystalline and magnetic characteristics (coercivity, squareness, magnetic phase, interactions and magnetization reversal modes) of NW arrays embedded in mild and hard anodized anodic aluminum oxide (AAO) templates with different pore diameters. The pulsed alternating current electrodeposition technique is proposed as a versatile approach in high-efficiency filling of the AAO templates, while also allowing for tuning magnetic properties of the resultant NWs. The first-order reversal curve analysis is also highlighted as an advanced characterization tool for nanomagnet arrays. Finally, potential cutting-edge nanoscale applications (magnetic information storage, energy storage and conversion, electronics, biosensing, microwave absorption and giant magnetoresistance) of magnetic NWs are presented.
... Lithographic patterning techniques relying on the selective elimination of materials to create topographies with preferred shape and size do not need further assembly steps. Well-established methodologies incorporating precise engineering control have made lithographic patterning techniques capable of developing 3D entities at the nanoscale [30][31][32][33][34]. Using the techniques, a variety of 3D constructs have been developed with different applications in biomedical devices [35][36][37][38], optoelectronics and electronics [39][40][41][42], microelectromechanical systems [43,44], and sensors [45][46][47][48]. However, these methods combine high costs with a relatively slow process, making the duration of production problematic. ...
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In recent decades, microfluidic techniques have been extensively used to advance hydrogel design and control the architectural features on the micro- and nanoscale. The major challenges with the microfluidic approach are clogging and limited architectural features: notably, the creation of the sphere, core-shell, and fibers. Implementation of batch production is almost impossible with the relatively lengthy time of production, which is another disadvantage. This minireview aims to introduce a new microfluidic platform, a vortex fluidic device (VFD), for one-step fabrication of hydrogels with different architectural features and properties. The application of a VFD in the fabrication of physically crosslinked hydrogels with different surface morphologies, the creation of fluorescent hydrogels with excellent photostability and fluorescence properties, and tuning of the structure–property relationship in hydrogels are discussed. We conceive, on the basis of this minireview, that future studies will provide new opportunities to develop hydrogel nanocomposites with superior properties for different biomedical and engineering applications.
... As a detector in a portable GC, this sensor could detect trace aliphatic amines extracted from sewage and rainwater through a liquid-liquid microextraction process. Recently, we prepared a chemiresistor from conductive polymer nanowires fabricated by soft lithography [80]. This sensor showed fast response and high sensitivity, both of which are required for high-performance GC detectors. ...
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Micro gas chromatography (μGC) has been continuously gaining attention since the last century owing to multiple favorable characteristics, such as its small size, low power consumption and minimal production and maintenance costs. μGC has the potential to provide practical solutions to emerging analytical challenges in security, health, and environment. In this review, we summarize recent advances in micro detectors for μGC, including the study of the miniaturization of conventional detectors and the development of novel detectors for μGC chromatography.
... Recently, chemiresistive gas sensors have attracted significant attention owing to their widespread and variety of applications including: (1) Indoor air quality monitoring (e.g., formaldehyde, benzene, carbon monoxide (CO), etc.) (Zhang et al., 2012;Saini et al., 2020;Marques et al., 2020); (2) Environmental air quality monitoring (e.g., greenhouse gas monitoring) (Honeycutt et al., 2019;Gupta et al., 2018;Bezzon et al., 2019;Manikandan et al., 2020); (3) Hazardous gas sensing (e.g., detecting explosion and toxic gases) (Lee et al., 2019;Duc et al., 2020;Kumar et al., 2020a); (4) Military applications (e.g., Chemical Warfare Agent) (Fennell et al., 2017;Jiang et al., 2018); (5) Food quality control and processing (e.g., prediction of meat freshness; detection of freshness of vegetables/fruits, and determining the time for freezing as well as the time of vegetables/fruits ripening) (Yousefi et al., 2019;Mustafa et al., 2020;Poyatos-Racionero et al., 2018); (6) Industrial production monitoring (e.g., methane sensing in mines; oil and gas positioning) (Honeycutt et al., 2019;Dai et al., 2020;Nikolic et al., 2020); (7) Agriculture industry (e.g., Ammonia (NH 3 ) acts as an anti-fungal agent and preservative in agriculture industry) (Kanaparthi et al., 2020;Ismail et al., 2020;Zhang et al., 2019b); (8) Automobile industry (e.g., sensing of polluted gases released from vehicles) Nazemi et al., 2019;Seekaew et al., 2019); (9) Animal and plant breeding (e.g., determining the time of cow oestrous) (Manzoli et al., 2019); (10) Medical care and disease diagnosis (e.g., detecting lung cancer, kidney malfunction, asthma, halitosis, and diabetes etc., can be evaluated through analyzing patients breath based on non-invasive nature and real time analysis) (Tang et al., 2020;Nasiri et al., 2019;Aroutiounian et al., 2020;Usman et al., 2019;Chen et al., 2019). Among these applications, indoor/outdoor air quality monitoring and environmental monitoring are highly demanded for maintaining standard air quality in the environment. ...
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Over the last few decades, various volatile organic compounds (VOCs) have been widely used in the processing of building materials and this practice adversely affected the environment i.e. both indoor and outdoor air quality. A cost-effective solution for detecting a wide range of VOCs by sensing approaches includes chemiresistive, optical and electrochemical techniques. Room temperature (RT) chemiresistive gas sensors are next-generation technologies desirable for self-powered or battery-powered instruments utilized in monitoring emissions that are associated with indoor/outdoor air pollution and industrial processes. The state-of-the-art overview of chemiresistive gas sensors is provided based on their attractive analytical characteristics such as high sensitivity, selectivity, reproducibility, rapid assay time and low fabrication cost. This review mainly discusses the recent advancement and advantages of graphene oxide (GO) nanocomposites-based chemiresistive gas sensors and various factors affecting their sensing performance at RT. Besides, the sensing mechanisms of GO nanocomposites-based chemiresistive gas sensors derived using metals, transition metal oxides (TMOs) and polymers were discussed. Finally, the challenges and future perspectives of GO nanocomposites-based RT chemiresistive gas sensors are also addressed.
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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.
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The advent of chemical sensors and biosensors has drawn tremendous attention particularly in the inspection of food quality. Array-based sensors take advantage of the integration of multiple recognition elements on a single microdetector, and the ability to recognize a myriad of molecular targets from complex samples. With the continuous advancement in lab-on-a-chip technology, microfluidic-based techniques have enabled rapid and portable monitoring of multiple nutritional or harmful substances that provide high sensitivity, high throughput, and low sample consumption. In this article, the latest progress in array-based chemical sensors and biosensors is carefully reviewed. Several major chemometric methods for handling high-dimensional data, including hierarchical cluster analysis, principal component analysis, and support vector machine, are introduced and commented of reference to their use primarily in the detection of foodborne hazardous species or contaminants. Finally, special insights are given into the development of miniaturized, sensitive, and selective sensors as the next generation of point-of-care tools.
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In this paper, an impedance-transduced sensor is developed based on a nanostructured graphene (GN) and poly (methyl methacrylate) (PMMA) sensing film for the detection of individual volatile organic compounds (VOCs) in aqueous media. Benefiting from a porous and high surface area, the nanostructured nanofiber is characterized by scanning electron microscopy (SEM) and optimized by the electrochemical impedance spectroscopy (EIS) technique. The recorded EIS data indicate the selective recognition of four VOCs of interest at a constant pH while there is no redox probe. The non-faradaic responses to each analyte at different concentrations are correlated with a three-element equivalent circuit (resistances of the solution and the film, and a pseudo-capacitance). To analyze the ability of the sensing film in distinguishing between VOCs with similar average boiling points, the values of the individual equivalent circuit elements are used as features and clustered in three-dimensional (3D) plots. Among the features, the two representing the maximum differences between the VOCs are represented in a two-dimensional (2D) plot to show the selectivity of the sensor. The feature extraction analysis demonstrates that the constant phase element (CPE) of the equivalent circuit is a more accurate predictor of VOCs than the interfacial capacitance. These results show high selectivity of the sensorial platform due to the synergistic pairing of nanostructured GN and PMMA.
Article
Chemiresistive sensors, particularly those based on nanostructures, have drawn increasing interest for application in security and environment monitoring, healthcare, biomedicine and others due to their high selectivity and sensitivity in detection of gaseous chemicals. Nanofibers possess large surface area, and unique electronic and optical properties that arise from the one-dimensional (1D) structures. They are an ideal candidate for development as sensors, even when constructed into heterojunction structures between n-type (electron acceptor) and p-type (electron donor) materials. Nanofibril heterojunctions created are highly tunable for enhancing the interfacial charge separation and transfer through modifying and optimizing both the material electronic structures and interface configuration spacing. This review aims to provide a comprehensive overview of the current state-of-the-art of chemiresistive gas sensors based on nanofibril heterojunctions, with special focus on the control of interfacial charge transfer which is critical to the sensor performances. Various nanofibril heterojunction structures will be summarized, including inorganic metal oxides, carbon materials, conjugated organic molecules, and functional polymers. The properties of precisely tunable interfaces are discussed, in conjunction with the sensor mechanisms. Potential limitations and challenges for these exciting materials and heterojunction structures for further sensor enhancement and application in real-world are also discussed. Lastly, an outlook is given on the future directions of developing nanofibril heterojunction sensors. This review will not only provide deep understanding of the structural design of nanofibril heterojunctions, and the interfacial charge transfer and chemiresistive sensor mechanisms, but moreover lay out more potentials for extending them into other electronic and optoelectronic applications.
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The demand for fast and ultratrace biomarkers detection is increasing in bioanalytical chemistry. In this work, highly ordered nanowires array and sensor integration are achieved with nanoscale printing approach. Negatively charged poly(3,4‐ethylenedioxythiophene)–poly(styrenesulfonate) doped with positively charged PEGylated biotin‐derivatized polyelectrolytes results a direct biofunctionalization on the nanowire surface without multiple postmodification steps. It provides homogeneous dispersed biofunctional sites and nonfouling surface on the nanowires. The ordered nanowires array enables the immunosensor to detect biotargets quickly and ultrasensitively. The nanowires impedimetric immunosensor is demonstrated for specific biomarkers detection and achieved a minimum responsive concentration as low as 10 pg mL−1 for protein biomarker and 10 CFU mL−1 for pathogen. A kind of biotin functionalization ink is achieved by doping with PEGylated biotin‐derivatized polyelectrolytes which enables a direct biofunctionalization on the nanowire surface. Then an immunosensor based on highly ordered nanowires array is fabricated by nanoscale printing approach. This sensor can be a general platform for different materials and various bioanalytical applications with ultrahigh sensitivity, trace detection, and fast response.
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The detection of volatile organic compounds is critical in various applications, e.g., medical care, environment monitoring, public security, agriculture, food industry, etc., requiring high sensitivity, good selectivity, fast response/recovery, multivariate data treatment, anti‐interferon, wide tolerance of gas temperature. In this work, taking advantage of the interface inside the composite thin film of contact electrification based sensor, a “fill two needs with one deed” strategy has been successfully demonstrated and developed to selectively detect volatile organic compounds (VOCs) without power source, which may shed a new light for VOCs sensing in the future sensor network. This article is protected by copyright. All rights reserved.
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Metal oxide nanostructures are the most promising materials for the fabrication of advanced gas sensors. However, the main challenge of these gas sensors is subject to humidity interference and issues related to the selectivity and high operating temperature which limits their response in real-time applications. In this study, we proposed nanohybrids of Pt-functionalized Al2O3/ZnO core-shell nanorods (NRs) for a real-time humidity-independent acetylene gas sensor. The core ZnO NRs have been fabricated on microelectromechanical system (MEMS) microheater, followed by a coating of a thin nanoscale moisture-blocking conformal Al2O3 shell by atomic layer deposition (ALD) and decoration of Pt NPs using photochemical deposition and e-beam evaporation. Prior to the fabrication, a COMSOL simulation was performed to optimize the microheater design and moisture-blocking layer thickness. A comparative study of the decoration of Pt NPs on ZnO surface by photochemical (s-Pt/ZnO) and e-beam evaporation (e-Pt/ZnO) and Al2O3 thin moisture-blocking shell layer (Pt/Al2O3/ZnO) in sensor response has been conducted. The fabricated sensors (s-Pt/ZnO) and (e-Pt/ZnO) showed a high response ∆R/R (%) of 96.46% and 68.15% to 200 ppm acetylene at 120 °C and detect trace concentrations of acetylene down to 1 ppm, but the response is influenced by humidity. Moreover, the sensor (Pt/Al2O3/ZnO) exhibited nearly the same sensing characteristics and high acetylene selectivity despite the wide range of humidity variation from 20% RH to 70% RH. The Pt-functionalized Al2O3/ZnO core-shell NRs-based sensor showed better sensing and stable performance than other sensors (s-Pt/ZnO and e-Pt/ZnO) under humidity conditions.
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The effective discrimination of dopamine (DA) analogues is an enduring challenge because of the very tiny structural differences, and thus separation technique is generally required during the conventional analysis. In this study, a hyperbranched polyethyleneimine (hPEI)-based fluorescent sensor array has been constructed for the separation-free and effective differentiation of four DA analogues. The discrimination includes two steps: firstly, the formation of fluorescent polymer nanoparticles (FPNs) with diverse emission profiles via hPEI-mediated self-polymerization reaction of DA analogues; secondly, the linear discriminant analysis of fluorescence patterns of formed FPNs for the differentiation of DA analogues. The hPEI-assisted self-polymerization reaction of DA analogues and substitution group mediated optical properties of the resulted FPNs enable an excellent discrimination of the four DA analogues at a concentration of 1.0 µM, when linear discriminant and hierarchical cluster analysis are smartly combined. Additionally, binary, tertiary and even quarternary mixture of analogues can also be well distinguished with the proposed sensor array. The practicability of this established sensor array is validated by a high accuracy (100%) evaluation of 88 blind samples containing a sole analogue or a mixture of two, three or four analogues.
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Gravimetric resonators based on Micro/Nanoelectromechanical System (M/NEMS) are potential candidates in developing smaller, less expensive, and higher performance gas sensors. Metal organic frameworks (MOFs), with high surface areas, recently come into focus as advanced nano-porous sensitive materials in micro gravimetric gas sensors. The surface of MOFs on those sensors is critical in offering water stability and varying absorption behaviors. However, the influences of surface on sensing performance are less explored and the strategy to tune surface properties of MOFs mounted on gravimetric resonators is still rare. In this paper, a straightforward strategy to engineer surface properties of MOFs, specifically Cu3(benzenetricarboxylate)2 (known as HKUST-1), is reported and the surface hydrophilicity/hydrophobicity of HKUST-1 is tuned by chemical vapor deposition combined with monolayer self-assembly. It is found out that the hybrid inorganic and organic surface engineering strategy not only preserves the absorption capacity of inner MOFs but also significantly enhances sensor stability toward water.
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Two-dimensional (2D) transition-metal carbides (Ti3C2T x MXene) have received a great deal of attention for potential use in gas sensing showing the highest sensitivity among 2D materials and good gas selectivity. However, one of the long-standing challenges of the MXenes is their poor stability against hydration and oxidation in a humid environment, limiting their long-term storage and applications. Integration of an effective protection layer with MXenes shows promise for overcoming this major drawback. Herein, we demonstrate a surface functionalization strategy for Ti3C2T x with fluoroalkylsilane (FOTS) molecules through surface treatment, providing not only a superhydrophobic surface, mechanical/environmental stability but also enhanced sensing performance. The experimental results show that high sensitivity, good repeatability, long-term stability, and selectivity and faster response/recovery property were achieved by the FOTS-functionalized when Ti3C2T x was integrated into chemoresistive sensors sensitive to oxygen-containing volatile organic compounds (ethanol, acetone). FOTS functionalization provided protection to sensing response when the dynamic response of the Ti3C2T x -F sensor to 30 ppm of ethanol was measured over in the 5 to 80% relative humidity range. Density functional theory simulations suggested that the strong adsorption energy of ethanol on Ti3C2T x -F and the local structure deformation induced by ethanol adsorption, contributing to the gas-sensing enhancement. This study offers a facile and practical solution for developing highly reliable MXene based gas-sensing devices with response that is stable in air and in the presence of water.
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The light-activated gas sensors have been investigated for their superior potential to replace current thermally-activated gas sensors which have several drawbacks for the Internet of Everything application. This review summarizes various efforts on the development of the light-activated gas sensors and provides an overview of the progress of them. The light-activated gas sensing properties of metal oxides, 2D materials, and other candidate materials are summarized. As strategies to overcome current challenges of the light-activated gas sensors, the effects of nanostructures and crystallographic orientations are discussed. Finally, the incorporation of plasmonic nanoparticles and integration with micro light-emitting diodes are proposed for the pathway toward the real application of the light-activated gas sensors. This review should offer a broad range of readers a new perspective toward the future development of the light-activated gas sensors.
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Gas sensors have become an integral part of the industrial & domestic sector, due to heavy harmful emissions (CO, NO2, SO2, CO2, NH3) from industries, automobiles. Metal oxide-semiconducting chemiresistive gas sensors (CRGS) are the most popular commercial gas sensors(GS) available in the market. However, they need high operational temperature for activation/deactivation, which is a serious concern for sensitive combustible environments, as well assign in other applications where flexibility, low power consumption & miniaturization are desirable. Hence, GS those exhibit high sensitivity & selectivity, at RT are desirable. The review focuses on various strategies & approaches employed, & the challenges ahead to realize RT CRGS. (i)1D-nanostructuring of various conventional metals & metal oxides; (ii)Nano+heterojunctions between metal oxide-metal oxides & noble metals; (iii)2D-materials; (iv)Self heating in nanowires; (v)Perovskites; (vi)Conducting polymers; (vii)defect engineering to produce free charge carriers; & (viii)alternative activation by light illumination. The mechanism behind the strategies implemented to achieve such RT gas sensing has been explicitly discussed. The review also introduces various types of GS, their working principle, pros & cons, mechanism & parameters of CRGS & their typical construction. This article also discusses the electrode configurations used in the chemiresistive gas sensors
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An impedance-transducer sensor was developed for in situ detection of hydrogen sulfide (H2S) and ammonia (NH3) in aqueous media. Using cyclic voltammetry (CV), polypyrrole (PPy) was deposited on the surface of the microfabricated interdigitated gold electrode. Due to the proton acid doping effect of H2S on PPy and ionic conduction of the film, the sensor showed a decreasing impedance response to H2S unlike other reducing chemicals, i.e., ammonia (NH3). The recorded faradaic data was then associated with an equivalent circuit and compared with that of NH3 to examine the selectivity of the sensor. An electrochemical impedance spectroscopy (EIS) analysis was applied to the mixture of H2S and NH3 prepared at different ratios for the concentrations ranging from 2 ppm – 20 ppm (below 2-ppm, no response was observed due to the formation of NH4HS, not sensible with PPy). The principal component analysis (PCA) was used to train a real-time prediction model for both classification (for the type of the analyte) and regression (the concentration of the analyte). The results showed the high performance of the sensor in determining individual analytes while the model was able to accurately predict the amount of H2S and NH3 in the mixture.
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Bioelectrochemistry is a rapidly growing field in which electrochemistry is combined with concepts from biochemistry, medicinal chemistry, and analytical chemistry to understand the properties and principles of biomolecule-electrode interactions. The integration of bioelectrochemistry with nanotechnology has led to the development of various types of enhanced biosensing capability. This chapter summarizes the different nanomaterials used in the fabrication of electrochemical biosensors, considering the effect of nanostructuring on biosensing performance. Besides this, different types of nanobiosensors are described, with emphasis on the nanostructure and fabrication, applicable to different biorecognition elements. Lastly, we discuss the combination of electrochemistry with surface plasmon resonance, a recently discovered, powerful technique for studying the binding kinetics of biorecognition events during electrochemical detection.
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Detection and recognition of chemical and biological species via sensor electronics are important not only for various sensing applications but also for fundamental scientific understanding. In the past two decades, sensor devices using one-dimensional (1D) nanowires have emerged as promising and powerful platforms for electrical detection of chemical species and biologically relevant molecules due to their superior sensing performance, long-term stability, and ultra-low power consumption. This paper presents a comprehensive overview of the recent progress and achievements in 1D nanowire synthesis, working principles of nanowire-based sensors, and the applications of nanowire-based sensor electronics in chemical and biological analytes detection and recognition. In addition, some critical issues that hinder the practical applications of 1D nanowire-based sensor electronics, including device reproducibility and selectivity, stability, and power consumption, will be highlighted. Finally, challenges, perspectives, and opportunities for developing advanced and innovative nanowire-based sensor electronics in chemical and biological applications are featured.
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A non-volatile memory capacitor is reported based on the polar-molecule system using a polymer as the dielectric. Two common dielectric polymers, polyvinyl pyridine (PVP) and polyvinyl alcohol (PVA), were studied, and their behavior was examined. To fabrication, the thin polymeric film layer was embedded between two electrodes to form a three-layer sandwich. The charge-voltage and pulse response characters were considered as the main resulted measurement. A memory window of 5 V was obtained by sweeping the applied voltage of the memory capacitor between ±10 V. Furthermore, the polarization role in charge-voltage hysteresis of the polymeric memory was confirmed with the permittivity–frequency measurement. The hysteresis was increased with the increasing of the polar branches existing inside the polymer. Sample in the uncrosslinked-polymer form displayed a large hysteresis, while no hysteresis was observed in photo-crosslinked ones. This selectivity in efficiency between uncrosslinked and photo-crosslinked samples enabled us to fabricate small size polymeric memory cells through a simple fabrication procedure. The presented memory capacitor shows repeatable, stable, and non-volatile memory behavior regarding data retention and erase/write operations for neuromorphic, printable, and biomedical applications.
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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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It is commonly believed that polymers are electrical insulators. However, the emergence of conducting polymers has challenged this traditional belief, and these materials have earned significant attention in recent years. The collaborative discovery of conductive polymers by Alan J. Heeger, Alan MacDiarmid, and Hideki Shirakawa won them the Nobel Prize in Chemistry in 2000. As conjugated carbon chains, conducting polymers are formed by the highly populated delocalized electronic system that is generated by π bonds in their structure. The optical and electrical behavior of conducting polymers are typically similar to that of semiconductors; however, conjugated polymers, unlike semiconductors, are not solids with atomic structure and are preferably shaped as an amorphous polymeric configuration. Therefore, processes, such as charge transfer in conducting polymers, can be entirely unrelated to semiconductors depending on the nature of the materials. A range of mechanisms can be active depending on the material processing. Conducting polymers have numerous promising applications in different analytical chemistry branches, including electrochemistry, spectroscopy, separation, and mass spectroscopy. Common conducting polymers include polyacetylene, polypyrrole, polyaniline, poly(para-phenylene), polythiophene, poly(p-phenylene vinylene), poly(3,4-ethylenedioxythiophene), polyacetylene, poly(p-phenylene sulfide), and polyfuran have been used widely. In this chapter, the history and application of conducting polymers in electrochemistry will be briefly discussed.
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We report on a selective hydrogen sulfide gas sensor based on zinc ferrite film which is obtained by a microwave-assisted solvothermal deposition route. The response of the chemiresistive device is found to be in the range of 1872% - 90% for 5.6 ppm - 0.3 ppm of H2S gas at an operating temperature of 250°C. The density functional theory studies suggest physisorption of the H2S molecules at the partially-inverted ZnFe2O4 surface as the reason behind the fast rise (of the order of 40 sec) and fall time (of the order of 70 sec) with complete recovery of the device. Finally, a dual-differential subtractor based auto-balancing interface circuit is proposed to drive this sensor which is advantageous in terms of accuracy and particularly suitable for a device such as ours, which has a wide dynamic range.
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In this study, we employed electrospinning technology and in situ polymerization to prepare wearable and highly sensitive PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors. PEDOT, PEDOT:PSS, and TiO2 were prepared via in situ polymerization and tested for characteristic peaks using energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR), then characterized using a scanning electron microscope (SEM), a four-point probe resistance measurement, and a gas sensor test system. The gas sensitivity was 3.46–12.06% when ethanol with a concentration between 12.5 ppm and 6250 ppm was measured; 625 ppm of ethanol was used in the gas sensitivity measurements for the PEDOT/composite conductive woven fabrics, PVP/PEDOT:PSS nanofiber membranes, and PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors. The latter exhibited the highest gas sensitivity, which was 5.52% and 2.35% greater than that of the PEDOT/composite conductive woven fabrics and PVP/PEDOT:PSS nanofiber membranes, respectively. In addition, the influence of relative humidity on the performance of the PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors was examined. The electrical sensitivity decreased with a decrease in ethanol concentration. The gas sensitivity exhibited a linear relationship with relative humidity lower than 75%; however, when the relative humidity was higher than 75%, the gas sensitivity showed a highly non-linear correlation. The test results indicated that the PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors were flexible and highly sensitive to gas, qualifying them for use as a wearable gas sensor platform at room temperature. The proposed gas sensors demonstrated vital functions and an innovative design for the development of a smart wearable device.
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Deoxygenation of graphene oxide is a low-cost and effective way to yield graphene (i.e., reduced graphene oxide - RGO) for many applications. However, choices of reduction approach and reduction time need consideration due to damaging pre-existing materials on electronic devices. Here, we found a facile and eco-friendly route that was based on the photo-oxidation of ethanol (diluted in water) on a catalytic TiO2 film to rapidly induce the formation of RGO within 15 min under UV (20 mW/cm²) or sun lights (1 sun = 100 mW/cm²). Our reduction route was indirectly activated by chain reactions of ethanol and TiO2 (so-called domino effect) because the GO deoxygenation occurred even when the samples were placed around and not in contact with TiO2 film. To obtain the highest reduction, the samples should stay on the catalytic film to receive lights for activation and acceleration of reactions. Furthermore, effects of exposure time (1–20 min), ethanol concentration (14.3–100%), and light intensity on RGO quality explored with the use of chemiresistive devices. The results of demonstrative sensing measurements towards NO2 and NH3 indicate that our method is promising for electrical applications using solution processable RGO.
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There is a growing demand for rapid analytical systems for detecting the presence of humans who are either entrapped as a result of a disaster or in particular hidden, as in the case of smuggling or trafficking. The trafficking and smuggling of people to Europe have reached epidemic proportions in recent years. This does not only put a major strain on European resources, but puts at risk the health and lives of the people being trafficked or smuggled. In this context, the early detection and interception of smuggled/trafficked people is of particular importance in terms of saving migrants from life-threatening situations. Similarly, the early and rapid location of entrapped people is crucial for urban search and rescue (USaR) operations organized after natural or man-made disasters. Since the duration of entrapment determines the survivability of victims, each novel detecting tool could considerably improve the effectiveness of the rescue operations and hence potentially save lives. Chemical analysis aiming at using a volatile chemical fingerprint typical for the presence of hidden humans has a huge potential to become an extremely powerful technology in this context. Interestingly, until now this approach has received little attention, despite the fact that trained dogs have been used for decades to detect the presence of buried people through scent. In this article we review the current status of using analytical techniques for chemical analysis for search and rescue operations, and discuss the challenges and future directions. As a practical implementation of this idea, we describe a prototype portable device for use in the rapid location of hidden or entrapped people that employs ion mobility spectrometry and a sensor array for the recognition of the chemical signature of the presence of humans.
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Resistive devices composed of one dimensional nanostructures are promising candidate for next generation gas sensors. However, the large-scale fabrication of nanowires is still a challenge, restricting the commercialization of such type of devices. Here, we reported a highly efficient and facile approach to fabricate poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) nanowire chemiresistive type of gas sensor by nanoscale soft lithography. Well-defined sub-100 nm nanowires are fabricated on silicon substrate which facilitates the device integration. The nanowire chemiresistive gas sensor is demonstrated for NH3 and NO2 detection at room-temperature and shows a limit of detection at ppb level which is compatible with nanoscale PEDOT:PSS gas sensors fabricated with conventional lithography technique. In comparison with PEDOT:PSS thin film gas sensor, the nanowire gas sensor exhibits a higher sensitivity and much faster response to gas molecules.
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In this paper, we have modeled and analyzed affinities and kinetics of volatile organic compounds (VOCs) adsorption (and desorption) on various surface chemical groups using multiple self-assembled monolayers (SAMs) functionalized film bulk acoustic resonator (FBAR) array. The high-frequency and micro-scale resonator provides improved sensitivity in the detections of VOCs at trace levels. With the study of affinities and kinetics, three concentration-independent intrinsic parameters (monolayer adsorption capacity, adsorption energy constant and desorption rate) of gas-surface interactions are obtained to contribute to a multi-parameter fingerprint library of VOC analytes. Effects of functional group's properties on gas-surface interactions are also discussed. The proposed sensor array with concentration-independent fingerprint library shows potential as a portable electronic nose (e-nose) system for VOCs discrimination and gas-sensitive materials selections.
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Combining vapour sensors into arrays is an accepted compromise to mitigate poor selectivity of conventional sensors. Here we show individual nanofabricated sensors that not only selectively detect separate vapours in pristine conditions but also quantify these vapours in mixtures, and when blended with a variable moisture background. Our sensor design is inspired by the iridescent nanostructure and gradient surface chemistry of Morpho butterflies and involves physical and chemical design criteria. The physical design involves optical interference and diffraction on the fabricated periodic nanostructures and uses optical loss in the nanostructure to enhance the spectral diversity of reflectance. The chemical design uses spatially controlled nanostructure functionalization. Thus, while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieve this goal using individual multivariable sensors. These colorimetric sensors can be tuned for numerous vapour sensing scenarios in confined areas or as individual nodes for distributed monitoring.
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In recent years, owing to the significant applications of health monitoring, wearable electronic devices such as smart watches, smart glass and wearable cameras have been growing rapidly. Gas sensor is an important part of wearable electronic devices for detecting pollutant, toxic, and combustible gases. However, in order to apply to wearable electronic devices, the gas sensor needs flexible, transparent, and working at room temperature, which are not available for traditional gas sensors. Here, we for the first time fabricate a light-controlling, flexible, transparentand working at room-temperature ethanol gas sensor by using commercial ZnO nanoparticles. The fabricated sensor not only exhibits fast and excellent photoresponse, but also shows high sensing response to ethanol under UV irradiation. Meanwhile, its transmittance exceeds 62% in the visible spectral range, and the sensing performance keeps the same even bent it at a curvature angle of 90(o). Additionally, using commercial ZnO nanoparticles provides a facile and low-cost route to fabricate wearable electronic devices.
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We report on ultrasensitive molecularly-modified silicon nanowire field effect transistor that marries between the lock-and-key and cross-reactive sensing worlds for the diagnosis of (gastric) cancer from exhaled volatolome. The sensor is able to selectively detect VOCs that are linked with gastric cancer conditions in exhaled breath and to discriminate them from environmental VOCs that would exist in exhaled breath samples but do not relate to the gastric cancer per se. Using breath samples collected from real patients with gastric cancer and from volunteers that have no cancer, blind analysis validated the ability of the reported sensor to discriminate between gastric cancer and control conditions, irrespective of important confounding factors such as tobacco consumption and gender with >85% accuracy. The reported sensing approach paves the way for utilizing the power of silicon nanowires in simple, inexpensive, portable, and non-invasive diagnosis of both cancer and other diseases conditions.
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Recently breath analysis has attracted a lot of attention for disease monitoring and clinical diagnostics as spectrometric techniques of high sophistication and novel sensing materials become available. Here advances in these technologies in connection to breath analysis are critically reviewed. A number of breath markers or tracer compounds are summarized and related to different diseases, either for diagnostics or for monitoring. Emphasis is placed on chemo-resistive gas sensors for their low cost and portability highlighting their potential and challenges for breath analysis as they start to be used in studies involving humans.
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We report a room-temperature NH3 gas sensor with high response and great long-term stability, including CeO2 NPs conformally coated by crosslinked PANI hydrogel. Such core-shell nanocomposites were prepared by in-situ polymerization with different weight ratios of CeO2 NPs and aniline. At room temperature, the nanohybrids showed enhanced response (6.5 to 50 ppm NH3), which could be attributed to p-n junctions formed by the intimate contact between these two materials. Moreover, the stability was discussed in terms of phytic acid working as a gelator which helped the PANI sheath accommodate itself and enhance the mechanical strength and chemical stability of the sensors by avoiding 'swelling effect' in high relative humidity. The sensors maintained its sensing characteristic (response of ca.6.5 to 50 ppm NH3) in 15 days. Herein, the obtained results could help to accelerate the development of ammonia gas sensor.
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A room temperature operating electronic nose (e-nose) has been developed by the assembly of conductive polymer nanocomposite (CPC) quantum resistive sensors (QRS). The fabrication of QRS by spray layer by layer (sLbL) of CPC solutions allowed us to obtain transducers with reproducible initial properties that could be easily tailored by adjusting either the number of sprayed layers and/or the solution composition. The selectivity of QRS was varied by changing the chemical nature of the polymer matrix in which carbon nanotubes (CNTs) were dispersed in solution, i.e., poly(carbonate) (PC), poly(caprolactone) (PCL), poly(lactic acid) (PLA), poly(styrene) (PS), and poly(methyl methacrylate) (PMMA). The e-nose was then successfully used to detect several volatile organic compounds (VOCs) selected among lung cancer biomarkers: a first set of seven polar vapours (water, ethanol, methanol, acetone, propanol, isopropanol, and 2-butanone), and another set of eleven less and nonpolar vapours (chloroform, toluene, benzene, styrene, cyclohexane, o-xylene, n-propane, n-decane, 1,2,4-trimethyl benzene, isoprene, and 1-hexene). The discrimination ability of the e-nose evaluated after a 3D principal component analysis (PCA) pattern recognition treatment was proved to be very good. Moreover, the quantitativity of the transducers' chemo-resistive responses was well fitted with the Langmuir–Henry-Clustering (LHC) model for both acetone and toluene vapours in a wide range of concentrations. The QRS developed in this study appear to be very good candidates to design low cost e-noses for the anticipated diagnosis of lung cancer by VOC analysis in breath, with ppm level sensitivity (tested down to 2.5 parts per million), short response time (a couple of seconds), low consumption, and a large signal to noise ratio (SNR ≥ 10).
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The design and development of a compact wireless gas sensor with a surface modified multiwalled carbon nanotube (f-CNT) chemiresistor as the sensing element is presented in this paper. f-CNT/polymer composite sensing film is patterned on a printed circuit board and is integrated to the wireless system. The change in resistance of the CNT/polymer composite film due to exposure of different gases is utilized as the principle of this gas sensor. The response for different organic vapors are evaluated and it is observed that the f-CNT/PMMA composite film shows fast response and change in resistance of the order of 102–103 due to its surface modification.
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We have demonstrated a NH 3 , NO 2 and water vapour sensor based on poly(m-aminobenzene sulfonic acid) functionalized single-walled carbon nanotube (SWNT–PABS) networks. The SWNT–PABS based sensors were fabricated by simple dispersion of SWNT–PABS on top of pre-fabricated gold electrodes. SWNT–PABS sensors showed excellent sensitivity with ppb v level detection limits (i.e., 100 ppb v for NH 3 and 20 ppb v for NO 2) at room temperature. The response time was short and the response was totally reversible. The sensitivity could be tuned by adjusting the sensor initial resistance. The sensors were also suitable for monitoring relative humidity in air.
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We measured the electronic properties and gas sensing responses of template-grown poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-based nanowires. The nanowires have a "striped" structure (gold-PEDOT/PSS-gold), typically 8um long (1um-6um-1um for each section, respectively) and 220 nm in diameter. Single-nanowire devices were contacted by pre-fabricated gold electrodes using dielectrophoretic assembly. A polymer conductivity of 11.5 +/- 0.7 S/cm and a contact resistance of 27.6 +/- 4 kOhm were inferred from measurements of nanowires of varying length and diameter. The nanowire sensors detect a variety of odors, with rapid response and recovery (seconds). The response (R-R0)/R0 varies as a power law with analyte concentration.
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The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.
Article
A simple computer-based screening technique has been developed for classifying human expired air components into 16 chemical classes, based on empirical formulas. The sort procedure was developed to simplify the screening of the composition of expired air samples by sorting all components into chemical classes and classifying components at the greater than 75% and greater than 90% occurrence levels. Both occurrence-rate components are then evaluated as diagnostic markers in a discriminant function model for their ability to detect lung cancer. Of the 386 components detected in the gas chromatography/mass spectrometry (GC/MS) data files, 45 components were present at the greater than 75% occurrence level and 28 components at the greater than 90% occurrence level. Thus, this preliminary sort routine, performed by using a simple macro program installed into a standard personal-computer spread-sheet, greatly reduces the amount of data required for statistical treatment. Such a sort routine can also be applied as easily to other complex GC/MS data files for the purpose of data reduction.
Article
This paper reported a high-performance e-nose type chemiresistive gas sensor composed of graphene oxide (GO) doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) nanowires. Large scale and well-defined sub-100 nm nanowires were prepared using nanoscale soft lithography in a highly efficient and facile way, facilitating subsequent device integration. The responses of the nanowire sensors to volatile organic compounds (VOCs) can be tuned by the different polymer components, which are utilized to constitute unique identification codes for ethanol, n-hexane, acetone and p-xylene and realize the discrimination of different VOCs. Besides, the score plot and classification matrix obtained respectively from the principal component analysis (PCA) and linear discriminant analysis (LDA) provide sufficient information to differentiate different VOCs.
Article
Volatile organic acids are important compounds contained in human body odor. The detection and recognition of volatile organic acids in human body odor are significant in many areas. The present study explored a possibility to use localized surface plasmon resonance (LSPR) of Au nanoparticles (AuNPs) and molecularly imprinted sol-gels (MISGs) as the sensitive layer to recognize typical organic acid odorants, propanoic acid (PA), hexanoic acid (HA), heptanoic acid (HPA) and octanoic acid (OA), from human body. The LSPR layer was prepared by vacuum sputtering of AuNPs on a glass substrate and consequently thermal annealing. The sensitive layer was fabricated by spin-coating molecularly imprinted titanate sol-gel on the AuNPs layer. A homemade optical device was developed to detect the change of transmittance, which was caused by the index changes of organic acid vapors where selecting absorbed by the MISG layers. It was found that compared with MISG coated samples, samples coated with non-imprinted sol gel (NISG) shown no responses to any acid vapors. For the MISG coated sensors, the LSPR sensitivity was affected by the spin coating speed. In addition, a sensor array based on MISGs with different templates (HA, HPA and OA) was constructed to detect the organic acids in single and their binary mixtures. The sensor response was analyzed by principal component analysis (PCA) and linear discriminant analysis (LDA). A 100% classification rate was achieved by leave-one-out cross-validation technique for LDA model. This work demonstrated that the MISGs coated LSPR sensor array has a great potential in organic acid odor recognition of human body odor.
Article
As a kind of facile tool, microfluidic paper-based analytical devices (μPADs) have been widely used in analytical and biomedical fields. However, because we lack the ability to control the continuous perfusion limits of these devices, they are not generally used in fields that require continuous flow, especially biofluidics fields such as cell culturing and drug screening. In this research, we design a novel, low-cost and compact platform that can be used to control the continuous perfusion of μPADs. As most of the parts of this platform can be created using a three-dimensional (3D) desktop printer, our platform can be easily duplicated by other researchers. We demonstrate that with our system, μPADs can be promising paper-based biofluidic platforms for cell culturing and drug screening.
Article
Point-of-care (POC) diagnostic technologies for early stage diagnosis and real-time monitoring of medical conditions are important elements of healthcare strategy to improve medical treatment outcomes. Graphene, one-atom-thick fabric of carbon, has attracted enormous attention as a new sensing platform for the development of new generation of nanoscale sensing devices. The two-dimensional (2D) nanostructure and high surface-to-volume ratio of graphene provide a strategy for designing sensing devices with capability to detect diverse analyte molecules. Their excellent conductivity and zero-band gap features promote electron transport between the sensor and analyte molecules, which is crucial for the development of ultra-fast-responsive and high sensitive devices for numerous biomedical applications. Particularly, owing to ease of fabrication and miniaturization, low cost, and simplicity of operation, graphene-based sensors offer a great potential for portable real-time medical diagnostics, when compared with conventional techniques based on expensive and labor extensive lab-bench instruments. This review provides a brief overview of recent progress in graphene-based sensors for the detection of volatile organic compounds (VOCs) and diagnosis of diseases via non-invasive analysis. Techniques for their fabrication of sensors and critical analysis of VOCs detection devices associated with various diseases are presented. We also summarized approaches to overcome the remaining obstacles to translate these research and development into real-world applications of sensors in clinical diagnosis.
Article
Since the sensing capability of semiconducting metal oxides was demonstrated in the 1960s, solid state gas sensors based on these materials have attracted considerable attention from both scientific and practical point of view. Because of the promising characteristics for detecting toxic gases and volatile organic compounds (VOCs) compared to conventional techniques, these devices are expected to play a key role in environmental monitoring, chemical process control, personal safety and so on in the near future. Therefore, in recent years, intensive studies have been conducted to improve their sensing performances, particularly to increase the sensitivity and detection limit of such devices. This can be accomplished by using metal oxide nanostructures with various shapes such as nanoparticles, nanowires, nanorods and nanotubes having sizes in the nanometer range. Owing to the high surface-to-volume ratios and consequently large number of surface sites exposed to target gas, nanostructured metal oxides enable a larger gas-sensing layer interaction and hence a higher sensitivity in comparison with conventional materials. This article extensively reviews recent developments in this field, focusing the attention on the detection of some common VOCs, including acetone (C3H6O), acetylene (C2H2), benzene (C6H6), cyclohexene (C6H10), ethanol (C2H5OH), formaldehyde (HCHO), n-butanol (C4H9OH), methanol (CH3OH) toluene (C7H8), and 2-propanol (C3H8O), by means of conductometric solid state sensors based on nanostructured semiconducting metal oxides.
Article
The development of high-performance volatile organic compound (VOC) sensor based on a p-type metal oxide semiconductor (MOS) is one of the important topics in gas sensor research because of its unique sensing characteristics, namely, rapid recovery kinetics, low temperature dependence, high humidity or thermal stability, and high potential for p–n junction applications. Despite intensive efforts made in this area, the applications of such sensors are hindered because of drawbacks related to the low sensitivity and slow response or long recovery time of p-type MOSs. In this study, the VOC sensing performance of a p-type MOS was significantly enhanced by forming a patterned p-type polycrystalline MOS with an ultrathin, high-aspect-ratio (~25) structure (~14 nm thickness) composed of ultrasmall grains (~5 nm size). A high-resolution polycrystalline p-type MOS nanowire array with a grain size of ~5 nm was fabricated by secondary sputtering via Ar+ bombardment. Various p-type nanowire arrays of CuO, NiO, and Cr2O3 were easily fabricated by simply changing the sputtering material. The VOC sensor thus fabricated exhibited higher sensitivity (ΔR/Ra = 30 at 1 ppm hexane using NiO channels), as well as faster response or shorter recovery time (~30 sec) than that of previously reported p-type MOS sensors. This result is attributed to the high resolution and small grain size of p-type MOSs, which lead to overlap of depleted zones; as a result, electrical properties are predominantly determined by surface states. Our new approach may be used as a route for producing high-resolution MOSs with particle sizes of ~5 nm within a highly ordered, tall nanowire array structure.
Article
An extra sensitive quartz crystal microbalance (QCM) gas sensor coated with thin PPy/TiO2 nanocomposite film was fabricated by using layer by layer self-assembly (SA) technology. The synthetic procedure and the resultant nanocomposites were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FE-SEM). It was found that an ultra-sensitive PPy/TiO2 nanocomposite film with very thin layer can be successfully obtained by. It was also found that the number of deposited layers strongly impacted on sensor response with ten bilayers showing best sensor performance. The obtained gas sensor coating with PPy/TiO2 sensitive film was found to exhibit a better performance with respect to sensor responses, which is based on frequency data. The resultant sensor represented high sensitivity toward 10 ppm of different targeted gases with evident frequency shift, fast response and recovery time. Long-term stability and excellent reversibility were also observed. In real-time application, a designed measurement set-up based on PPy/TiO2 based sensor showed a good ability on shelf-life evaluation of foodstuffs (mango, egg and fish). The resulting QCM based gas sensor coated with PPy/TiO2 nanocomposite via Layer by Layer self-assembly presented a promising capability to detect trace irritant gases and food quality evaluation.
Article
Formaldehyde (FA) is a potential breath marker for lung cancer and a tracer for indoor air quality monitoring. Its typical concentrations are below 100 ppb posing a sensitivity and selectivity challenge to current portable sensor systems. Here, we present a highly sensitive, selective and compact electronic nose (E-nose) for real-time quantification of FA at realistic conditions. This E-nose consists of four nanostructured and highly porous Pt-, Si-, Pd- and Ti-doped SnO2 sensing films directly deposited onto silicon wafer-based microsubstrates by flame spray pyrolysis (FSP). The constituent sensors offer stable responses (24 h tested) and detection of FA down to 3 ppb (signal-to-noise ratio > 25) at breath-realistic 90% relative humidity. Each dopant induces different analyte selectivity enabling selective detection of FA in 2- and 4-analyte mixtures by multivariate linear regression. In simulated breath (FA with higher acetone, NH3 and ethanol concentrations), FA is detected with an average error ≤ 9 ppb using the present E-nose and overcoming selectivity issues of single sensors. This device could facilitate easy screening of lung cancer patients and monitoring of indoor FA concentrations.
Article
Monitoring toxic Chlorine (Cl2) at the parts-per-billion (ppb) level is crucial for safe usage of this gas. Herein, ZnO, WO3, and SnO2 nanowire sensors were fabricated using an on-chip growth technique with chemical vapour deposition. The Cl2 gas-sensing characteristics of the fabricated sensors were systematically investigated. Results demonstrated that SnO2 nanowires exhibited higher sensitivity to Cl2 gas than ZnO and WO3 nanowires. The response (RCl2/Rair) of the SnO2 nanowire sensor to 50 ppb Cl2 at 50°C was about 57. Hence, SnO2 nanowires can be an excellent sensing material for detecting Cl2 gas at the ppb level under low temperatures. Abnormal sensing characteristics were observed in the WO3 and SnO2 nanowire sensors at certain temperatures; in particular, the response level of these sensors to 5 ppm Cl2 was lower than that to 2.5 ppm Cl2. The sensing mechanism of the SnO2 nanowire sensor was also elucidated by determining Cl2 responses under N2 and dry air as carrier gases. We proved that the Cl2 molecule was first directly adsorbed on the metal oxide surface and was then substituted for pre-adsorbed oxygen, followed by lattice oxygen.
Article
In this work, we report the fabrication of gas sensors prepared by in situ polymerization of aniline on non-woven fabrics. It is anticipated that a thin coating of polyaniline film fabricated on porous fabric material would improve the performance of the polyaniline based gas sensor. The hypothesis is based on the recent improved technique that allows the fabrication of nanoparticle based polyaniline film, and the high gas permeability of the fabrics. Sensor fabrication parameters which included acidity of reaction media, precursor and reagent concentrations, and the number of modification cycle have been studied. The resulting gas sensors were found to be highly responsive to a range of volatile organic compounds (VOCs). This high sensitivity was also accompanied with fast response time (similar to 10 s). The order of sensitivity to VOCs was found to be ethanol > chloroform > toluene > acetone > ethyl acetate. Further, the sensor was three orders of magnitude more sensitive to ammonia than all organic vapours tested.
Article
Nanoscale circuits are fabricated by assembling different conducting materials (e.g., metal nanoparticles, metal nano-wires, graphene, carbon nanotubes, and conducting polymers) on inkjet-printing patterned substrates. This nonlitho-graphy strategy opens a new avenue for integrating conducting building blocks into nanoscale devices in a cost-efficient manner. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Article
A comprehensive study on the chemiresistive responses of an array of noncovalent metalloporphyrin-SWCNT-based sensors to various classes of volatile organic carbons (VOCs) was reviewed. The device was fabricated from complexes of meso-tetraphenylporphyrin (tppH2). For sensing measurements, VOC was diluted in N2 gas into an enclosure holding the device. The VOC concentrations were 1000 ppm except for alkanes and for amines. A potentiostat applied 0.100 V across the electrodes and recorded current for at least three 60 s VOC exposures and 180 s of N2 between exposures. After baseline correction, the change in current is converted to negative change in conductance. With the exception of amines, the basis of differentiation appears to correlate with the solubilities of the porphyrin complexes in the analytes, suggesting that swelling contributes to responses. This work shows that porphyrin-CNT composites have potential in identification of VOCs, which may lead to uses in environmental monitoring, security, and healthcare diagnostics.
Article
Gas sensors can detect combustible, explosive and toxic gases, and have been widely used in safety monitoring and process control in residential buildings, industries and mines. Recently, graphene-based hybrids were widely investigated as chemiresistive gas sensors with high sensitivity and selectivity. This systematic review is therefore timely and necessary to evaluate the success of graphene-based hybrids on gas detection and to identify their challenges. We review the sensing principles and the synthesis process of the graphene-based hybrids with noble metals, metal oxides and conducting polymers to achieve better understanding and design of novel gas sensors. Our review will assist researchers to understand the evolution and the challenges of graphene-based hybrids, and create interest in development of gas-sensing techniques.
Article
In order to fabricate textile-based flexible VOC sensors, two conductive polymers such as polyaniline and poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) (PEDOT:PSS) were used as VOC-sensing materials, and various porous organic membranes were used as base substrates on which the conductive polymers were coated. Electrical resistance change of conductive polymers by adsorption of VOCs was measured. Polyaniline showed better sensitivity than PEDOT:PSS. Porous high density polyethylene membrane exhibited the most stable signal reproducibility and dimensional stability of membrane itself. Even after covering with additional high density polyethylene membrane to protect conductive polyaniline inside, the stable signals were still obtained during repeated measurement.
Article
In this work, a new optical gas sensor using thin polymer layers was developed. The polymer sensing layers were synthesized by chemical polymerization using the distilled aniline. The optical property of a polymer as a sensing material was analyzed using UV-Vis-NIR. These layers were prepared using centrifugal force. The polymer layer was uniformly deposited on inner glass pillar. The light source was red-light emitting diode (LED) with a 655 nm wavelength. The light power transmitted through the guide cell was measured with a photodiode. Variation of the light power transmitted was detected when the gas was absorbed into the polymer layer. The transmitted light intensity decreased because gas molecules were absorbed into the polymer layer. This optical sensor showed a good sensitivity to NH3 gas.
Article
Conducting polymernanostructures are emerging materials with tremendous potential for conductometric/field effect transistor (FET) bio/chemical sensors because of their chemical sensitivity and biocompatibility. Herein, we review recent developments in conducting polymernanowire-based sensors and discuss the impact of several milestones and continuing challenges. Particular attention is given to device fabrication, nanostructure performance enhancement, and functionalization schemes. Several assembly and integration techniques have been developed for single nanowire devices but significant progress is still needed to improve scalability and manufacturability. Future work should focus on high throughput approaches that enable combinatorial screening of conducting polymernanowires and heterogeneous, high density arrays of conducting polymernanostructures, deterministically tailored for targeted analytes. The spatial and temporal resolution of conducting polymernanowires is addressed along with the origin of the sensitivity enhancement. Functionalization routes add another degree of complexity for biosensors and are discussed in the context of nanosensor performance and device fabrication.
Article
The principle, construction, and applications of piezoelectric crystal sensors as universal sensor are reviewed. A historical overview and basic piezoelectric crystal physics as well as design considerations for different sensor system are reviewed. Most of previous reviews were treated with gas phase application, but this review is focused mainly on the liquid phase application, such as monitoring the dynamic microrheology phenomena of liquid crystal, lipid thin films, and electrochemical polymerized polypyrrole film.
Article
CeO2-doped ZnO thin-film gas sensors with different Ce/Zn ratios have been fabricated by dip-coating method, starting from zinc acetate dihydrate, cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and anhydrous ethanol. Each layer was fired at 180°C in a conventional oven for 30min and the final coatings were sintered at 500°C in a muffle furnace for 60min. The microstructure and morphology of the films were characterized by XRD and FESEM, respectively. The resistance and sensitivities to volatile organic compounds were investigated on the static testing chamber. The X-ray diffraction (XRD) analysis of the films reveals the appearance of CeO2, tetravalent cerium dioxide whose valency is different from cerium nitrate hexahydrate. The results also show that as-prepared thin films with thickness of about 5μm are polycrystalline with the structure of hexagonal wurtzite type. They consist of almost spherical particles with size ranging from 40 to 65nm. Pure ZnO and Ce-doped ZnO thin-film sensors were prepared and tested for specific sensitivity to alcohol, acetone and benzene. It is observed that 1at.% Ce–ZnO and 5at.% Ce–ZnO are more sensitive to volatile organic compounds (VOCs), compared with other films with the different dopant concentration. The sensitivity of 5at.% Ce–ZnO thin-film sensors to 100ppm alcohol reaches 80 or so at 320°C. 5at.% Ce–ZnO thin-film sensors show good selectivity to alcohol, and thus can serve as alcohol-sensing sensors. A new physical model of the CeO2 dopant influence on the gas-sensing properties of ZnO thin films is proposed. The addition of Ce to ZnO modified the particles size distribution, electrical conductivity, the catalytic activity and thus affected gas-sensing property to some extent.
Article
Molecularly modified silicon nanowire field effect transistors (SiNW FETs) are starting to appear as promising devices for sensing various volatile organic compounds (VOCs). Understanding the connection between the molecular layer structure attached to the SiNWs and VOCs is essential for the design of high performance sensors. Here, we explore the chain length influence of molecular layers on the sensing performance to polar and nonpolar VOCs. SiNW FETs were functionalized with molecular layers that have similar end (methyl) group and amide bridge bond, but differ in their alkyl chain lengths. The resulting devices were then exposed to polar and nonpolar VOCs in various conditions. Our results showed that the sensing response to changing the threshold voltage (ΔVth) and changing the relative hole mobility (Δµh/µh-a) have a proportional relationship to the VOC concentration. On exposure to a specific VOC concentration, ΔVth response increased with the chain length of the molecular modification. In contrast, Δµh/µh-a did not exhibit any obvious reliance on the chain length of the molecular layer. Analysis of the responses with an electrostatic-based model suggests that the sensor response in ΔVth is dependent on the VOC concentration, VOC vapor pressure, VOC-molecular layer binding energy, and VOC adsorption induced dipole moment changes of molecular layer. Understanding the relationship between the silicon nanowires' molecular layer structure and the VOCs is essential for the design of high performance sensors.
Article
Molecular layers attached to silicon nanowire field effect transistor (SiNW FET) can serve as antennas for signal transduction of volatile organic compounds (VOCs). Nevertheless, the mutual relationship between molecular layers and VOCs still puzzles. In the present paper, we explore the effect of molecular layer's end (functional) groups on sensing properties of VOCs. Towards this end, SiNW FETs were modified with tailor-made molecular layers that have same backbone but differ in their end groups. Changes in the threshold voltage (ΔVth) and changes in the mobility (Δµh) were then recorded upon exposure to various VOCs. Model-based analysis indicates that the interaction between molecular layers and VOCs can be classified to three main mechanisms: (a) dipole-dipole interaction between the molecular layer and the polar VOCs; (b) induced dipole-dipole interaction between the molecular layers and the nonpolar VOCs; and (c) molecular layer tilt as a result of VOCs diffusion. With these mechanism in mind, it was found that the electron-donating/withdrawing properties of functional groups were shown to control dipole moment orientation of adsorbed VOCs and, as a result, determine the direction (or sign) of △Vth. Additionally, the diffusion of VOCs into the molecular layer, determined by the type of functional groups, is the main reason for the △µh responses. The reported findings and sensing model are expected to provide an efficient way to design chemical sensors that are based on SiNW FETs to nonpolar VOCs, which do not exchange carriers with the molecular layers.
Article
In this paper we review recent progress in materials, fabrication processes, device designs, and applications related to organic thin-film transistors (OTFTs), with an emphasis on papers published during the last three years. Some earlier papers that played an important role in shaping the OTFT field are included, and a number of previously published review papers that cover that early period more completely are referenced. We also review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
Article
An array with five SAW sensors using different kinds of polymers was fabricated to detect chemical agents and their gas response characteristics were extensively investigated. The SAW devices with different interdigital transducer (IDT) electrode line widths of 3, 4, 6, 8 and 20 m, which corresponded to the central frequencies of 264, 198, 132, 99 and 39.6 MHz, respectively, were designed. The IDT electrodes consisted of 100 finger pairs of 200 nm thick aluminum films. The polymers used as the sensing materials were polyisobutylene (PIB), polyepichlorohydrin (PECH), polydimethylsiloxane (PDMS), polybutadiene (PBD) and polyisoprene (PIP). The thin films were coated on a quartz substrate by spin coating technique. Four simulant gases of chemical warfare agents of dimethylmethylphosphonate (DMMP), acetonitrile (CH 3 CN), dichloromethane (CH 2 Cl 2) and dichloropentane (DCP) were used as target gases, instead of the real nerve, blood, choking and vesicant agents. After spin coating of PIB and PECH, the substrate was heated at 65 • C in N 2 ambient for 1 h to remove the cyclohexane and ethylacetate, which were used as solvents. PDMS films were heated at 75 • C in a N 2 flow for 2 h to remove the ethylacetate used as a solvent. And PBD and PIP were heated at 60 • C in a N 2 flow for 1 h to remove the benzene used as a solvent. The sensing characteristics of the SAW sensors were measured by using E-5061A network analyzer. The polymer SAW sensor array showed good selectivity to simulant gases. Principal component analysis (PCA) was adapted to classify the chemical warfare agents.
Article
A study was conducted to demonstrate a new method to prepare chemically patterned flat PDMS stamps using nanoimprint lithography (NIL). NIL was demonstrated to be a high-volume and cost-effective patterning technique with sub-10 nm resolution. It involved the pressing of a hard mold nanoscale feature into a thin polymer film that had been coated on a substrate, deforming its shape according to the features of the mold and a relief pattern in the polymer layer. It was demonstrated that the patterned polymer had the potential to be processed by reactive ion etching to transfer the pattern onto the underlying substrate. The NIL-patterned polymer film was used on a flat PDMS substrate as a mask in the oxidation step to fabricate the chemically patterned flat stamp. The chemical patterns were also formed by gas-phase evaporation of a fluorinated silane.