Search

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Two-dimensional (2D) nanostructures are gaining tremendous interests due to the fascinating physical, chemical, electrical, and optical properties. Recent advances in 2D nanomaterials synthesis have contributed to optimization of various parameters such as physical dimension and chemical structure for specific applications. In particular, development of high performance gas sensors is gaining vast importance for real-time and on-site environmental monitoring by detection of hazardous chemical species. In this review, we comprehensively report recent achievements of 2D nanostructured materials for chemiresistive-type gas sensors. Firstly, the basic sensing mechanism is described based on charge transfer behavior between gas species and 2D nanomaterials. Secondly, diverse synthesis strategies and characteristic gas sensing properties of 2D nanostructures such as graphene, metal oxides, transition metal dichalcogenides (TMDs), metal organic frameworks (MOFs), phosphorus, and MXenes are presented. In addition, recent trends in synthesis of 2D heterostructures by integrating two different types of 2D nanomaterials and their gas sensing properties are discussed. Finally, this review provides perspectives and future research directions for gas sensor technology using various 2D nanomaterials. Graphical Abstract

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

Hydrogen (H2) is a flammable gas, and even tiny leaks of H2 must be detected for safety. However, the detection of low levels (below ppm) of H2 in air still remains an unmet challenge. Herein, we present a facile synthesis of bimetallic nanoparticles (BM-NPs) by using porous ion-exchange polymers in order to develop superior H2 sensors. The porous ion-exchange polymers enable the versatile fabrication of ultra-small BM-NPs on various supports. In particular, PdPt NPs derived from our method show excellent H2-sensing performances at room temperature in air, with an ultra-low detection limit (0.4 ppm), as a result of the synergistic effect of PdPt NPs on H2 sensing. We further developed a wireless H2-sensing system by combining PdPt NPs with radio-frequency communication. Our method can not only pave a new way in the field of H2 sensors but also be easily extended to the fabrication of various ultra-small BM-NPs for diverse applications needed the superior activity of BM-NPs. © 2020 Elsevier Inc.Bimetallic nanoparticles (BM-NPs) have attracted much attention in catalysis, sensing, and electronics as a result of their ultra-high activity for surface reactions. For reliable utilization of BM-NPs in various applications, robust synthetic methods for the creation of non-aggregated functional BM-NPs with diameters less than a few nanometers are needed. Herein, we present functional assemblies of ultra-small BM-NPs produced within high-stability porous ion-exchange polymers. Specifically, PdPt NPs can be readily produced with precision dimensional control down to 1 nm. These PdPt NPs with porous polymers display superior hydrogen (H2)-sensing properties at room temperature in air. We achieve an ultra-low limit of detection (H2 0.4 ppm), thereby confirming the outstanding sensing performance of the PdPt NPs. We further demonstrate a wireless H2-sensing system by combining porous polymer-templated PdPt NPs with a radio-frequency identification (RFID) system, which enables the

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

Hydrogen (H2) is a flammable gas, and even tiny leaks of H2 must be detected for safety. However, the detection of low levels (below ppm) of H2 in air still remains an unmet challenge. Herein, we present a facile synthesis of bimetallic nanoparticles (BM-NPs) by using porous ion-exchange polymers in order to develop superior H2 sensors. The porous ion-exchange polymers enable the versatile fabrication of ultra-small BM-NPs on various supports. In particular, PdPt NPs derived from our method show excellent H2-sensing performances at room temperature in air, with an ultra-low detection limit (0.4 ppm), as a result of the synergistic effect of PdPt NPs on H2 sensing. We further developed a wireless H2-sensing system by combining PdPt NPs with radio-frequency communication. Our method can not only pave a new way in the field of H2 sensors but also be easily extended to the fabrication of various ultra-small BM-NPs for diverse applications needed the superior activity of BM-NPs. © 2020 Elsevier Inc.Bimetallic nanoparticles (BM-NPs) have attracted much attention in catalysis, sensing, and electronics as a result of their ultra-high activity for surface reactions. For reliable utilization of BM-NPs in various applications, robust synthetic methods for the creation of non-aggregated functional BM-NPs with diameters less than a few nanometers are needed. Herein, we present functional assemblies of ultra-small BM-NPs produced within high-stability porous ion-exchange polymers. Specifically, PdPt NPs can be readily produced with precision dimensional control down to 1 nm. These PdPt NPs with porous polymers display superior hydrogen (H2)-sensing properties at room temperature in air. We achieve an ultra-low limit of detection (H2 0.4 ppm), thereby confirming the outstanding sensing performance of the PdPt NPs. We further demonstrate a wireless H2-sensing system by combining porous polymer-templated PdPt NPs with a radio-frequency identification (RFID) system, which enables the

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

Hydrogen (H2) is a flammable gas, and even tiny leaks of H2 must be detected for safety. However, the detection of low levels (below ppm) of H2 in air still remains an unmet challenge. Herein, we present a facile synthesis of bimetallic nanoparticles (BM-NPs) by using porous ion-exchange polymers in order to develop superior H2 sensors. The porous ion-exchange polymers enable the versatile fabrication of ultra-small BM-NPs on various supports. In particular, PdPt NPs derived from our method show excellent H2-sensing performances at room temperature in air, with an ultra-low detection limit (0.4 ppm), as a result of the synergistic effect of PdPt NPs on H2 sensing. We further developed a wireless H2-sensing system by combining PdPt NPs with radio-frequency communication. Our method can not only pave a new way in the field of H2 sensors but also be easily extended to the fabrication of various ultra-small BM-NPs for diverse applications needed the superior activity of BM-NPs. © 2020 Elsevier Inc.Bimetallic nanoparticles (BM-NPs) have attracted much attention in catalysis, sensing, and electronics as a result of their ultra-high activity for surface reactions. For reliable utilization of BM-NPs in various applications, robust synthetic methods for the creation of non-aggregated functional BM-NPs with diameters less than a few nanometers are needed. Herein, we present functional assemblies of ultra-small BM-NPs produced within high-stability porous ion-exchange polymers. Specifically, PdPt NPs can be readily produced with precision dimensional control down to 1 nm. These PdPt NPs with porous polymers display superior hydrogen (H2)-sensing properties at room temperature in air. We achieve an ultra-low limit of detection (H2 0.4 ppm), thereby confirming the outstanding sensing performance of the PdPt NPs. We further demonstrate a wireless H2-sensing system by combining porous polymer-templated PdPt NPs with a radio-frequency identification (RFID) system, which enables the

Single-walled carbon nanotubes (SWCNTs) are recognized as versatile materials for the formation of chemiresistive sensors. However, imparting high sensitivity and selectivity to SWCNTs remains a major challenge. Herein, we report a new sensory system that interfaces SWCNTs and catalytic metal nanoparticles (NPs) in a film of a porous ion exchange polymer to produce sensitive and selective sensors. The porous polymer films are based on imidazolium-functionalized triptycene polyether sulfone, and the environment created by this polymer results in the formation of ultrasmall (<5 nm) Au NPs. The polymer serves to suppress the growth of Au NPs while maintaining gas transport. The size control promotes strong interactions between Au NPs and carbon monoxide (CO), and this composition produces a robust, sensitive, and selective CO chemiresistive sensor. We further demonstrate that the modulation of a gate voltage in chemical field-effect transistor sensing devices enhances the performance by promoting the activity of Au NPs. The sensors display an increase of CO response at room temperature in air under the negative gate voltage. Our results demonstrate that the combination of a porous ion exchange matrix, NPs, and gate voltage-modulated chemiresistors can be synergistically tuned to create sensitive and selective sensors for target analytes., National Science Foundation (Grant DMR-1809740)

Hydrogen (H2) is a flammable gas, and even tiny leaks of H2 must be detected for safety. However, the detection of low levels (below ppm) of H2 in air still remains an unmet challenge. Herein, we present a facile synthesis of bimetallic nanoparticles (BM-NPs) by using porous ion-exchange polymers in order to develop superior H2 sensors. The porous ion-exchange polymers enable the versatile fabrication of ultra-small BM-NPs on various supports. In particular, PdPt NPs derived from our method show excellent H2-sensing performances at room temperature in air, with an ultra-low detection limit (0.4 ppm), as a result of the synergistic effect of PdPt NPs on H2 sensing. We further developed a wireless H2-sensing system by combining PdPt NPs with radio-frequency communication. Our method can not only pave a new way in the field of H2 sensors but also be easily extended to the fabrication of various ultra-small BM-NPs for diverse applications needed the superior activity of BM-NPs.

A bioelectronic nose, an intelligent chemical sensor array system coupled with bio-receptors to identify gases and vapours, resembles mammalian olfaction by which many vertebrates can sniff out volatile organic compounds (VOCs) sensitively and specifically even at very low concentrations. Olfaction is undertaken by the olfactory system, which detects odorants that are inhaled through the nose where they come into contact with the olfactory epithelium containing olfactory receptors (ORs). Because of its ability to mimic biological olfaction, a bio-inspired electronic nose has been used to detect a variety of important compounds in complex environments. Recently, biosensor systems have been introduced that combine nanoelectronic technology and olfactory receptors themselves as a source of capturing elements for biosensing. In this article, we will present the latest advances in bioelectronic nose technology mimicking the olfactory system, including biological recognition elements, emerging detection systems, production and immobilization of sensing elements on sensor surface, and applications of bioelectronic noses. Furthermore, current research trends and future challenges in this field will be discussed. Keywords: bioelectronic nose; olfactory receptor; OR; odour analysis; biosensor

Macroporous WO₃ nanotubes (NTs) functionalized with nanoscale catalysts were fabricated using coaxial electrospinning combined with sacrificial templating and protein-encapsulated catalysts. The macroporous thin-walled nanotubular structures were obtained by introducing colloidal polystyrene (PS) particles to a shell solution of W precursor and poly(vinylpyrrolidone). After coaxial electrospinning with a core liquid of mineral oil and subsequent calcination, open pores with an average diameter of 173 nm were formed on the surface of WO₃ NTs due to decomposition of the PS colloids. In addition, catalytic Pd nanoparticles (NPs) were synthesized using bio-inspired protein cages, i.e., apoferritin, and uniformly dispersed within the shell solution and subsequently on the WO₃ NTs. The resulting Pd functionalized macroporous WO₃ NTs were demonstrated to be high performance hydrogen (H₂) sensors. In particular, Pd-functionalized macroporous WO₃ NTs exhibited a very high H₂ response (R[subscript air]/R[subscript gas]) of 17.6 at 500 ppm with a short response time. Furthermore, the NTs were shown to be highly selective for H₂ compared to other gases such as carbon monoxide (CO), ammonia (NH₃), and methane (CH₄). The results demonstrate a new synthetic method to prepare highly porous nanotubular structures with well-dispersed nanoscale catalysts, which can provide improved microstructures for chemical sensing., Intel Corporation

Macroporous WO₃ nanotubes (NTs) functionalized with nanoscale catalysts were fabricated using coaxial electrospinning combined with sacrificial templating and protein-encapsulated catalysts. The macroporous thin-walled nanotubular structures were obtained by introducing colloidal polystyrene (PS) particles to a shell solution of W precursor and poly(vinylpyrrolidone). After coaxial electrospinning with a core liquid of mineral oil and subsequent calcination, open pores with an average diameter of 173 nm were formed on the surface of WO₃ NTs due to decomposition of the PS colloids. In addition, catalytic Pd nanoparticles (NPs) were synthesized using bio-inspired protein cages, i.e., apoferritin, and uniformly dispersed within the shell solution and subsequently on the WO₃ NTs. The resulting Pd functionalized macroporous WO₃ NTs were demonstrated to be high performance hydrogen (H₂) sensors. In particular, Pd-functionalized macroporous WO₃ NTs exhibited a very high H₂ response (R[subscript air]/R[subscript gas]) of 17.6 at 500 ppm with a short response time. Furthermore, the NTs were shown to be highly selective for H₂ compared to other gases such as carbon monoxide (CO), ammonia (NH₃), and methane (CH₄). The results demonstrate a new synthetic method to prepare highly porous nanotubular structures with well-dispersed nanoscale catalysts, which can provide improved microstructures for chemical sensing., Intel Corporation

We have investigated the effect of texture on in-plane (IPP) and out- of plane (OPP) polarizations of pulsed-laser-deposited BaTiO3 thin films grown on Pt and La0.5Sr0.5CoO3 (LSCO) buffered Pt electrodes. The OPP and IPP polarizations were observed by piezoresponse force microscopy (PFM) for three-dimensional polarization analyses in conjunction with conventional diffraction methods using x-ray diffraction and reflection high energy electron diffraction measurements. BaTiO3 films grown on Pt electrodes exhibited highly (101) preferred orientation with higher IPP component whereas BaTiO3 film grown on LSCO/Pt electrodes showed (001) and (101) orientations with higher OPP component. Measured effective d(33) values of BaTiO3 films deposited on Pt and LSCO/ Pt electrodes were 14.3 and 54.0 pm/ V, respectively. Local piezoelectric strain loops obtained by OPP and IPP-PFM showed that piezoelectric properties were strongly related to film orientation.

We have investigated the effect of texture on in-plane (IPP) and out- of plane (OPP) polarizations of pulsed-laser-deposited BaTiO3 thin films grown on Pt and La0.5Sr0.5CoO3 (LSCO) buffered Pt electrodes. The OPP and IPP polarizations were observed by piezoresponse force microscopy (PFM) for three-dimensional polarization analyses in conjunction with conventional diffraction methods using x-ray diffraction and reflection high energy electron diffraction measurements. BaTiO3 films grown on Pt electrodes exhibited highly (101) preferred orientation with higher IPP component whereas BaTiO3 film grown on LSCO/Pt electrodes showed (001) and (101) orientations with higher OPP component. Measured effective d(33) values of BaTiO3 films deposited on Pt and LSCO/ Pt electrodes were 14.3 and 54.0 pm/ V, respectively. Local piezoelectric strain loops obtained by OPP and IPP-PFM showed that piezoelectric properties were strongly related to film orientation.