Recent Progress of Nanostructured Sensing Materials from 0D to 3D: Overview of Structure-Property-Application Relationship for Gas Sensors

Progress of 0D Biomass-Derived Porous Carbon Materials Produced by Hydrothermal Assisted Synthesis for Advanced Supercapacitors

Supercapacitors are garnering considerable interest owing to their high-power density, rapid charge-discharge capability, and long cycle life. Among the various materials explored, biomass-derived carbon nanomaterials stands out as a sustainable and cost-effective choice, thanks to its natural abundance and eco-friendly characteristics. This review delineates recent advances in the synthesis of zero-dimensional (0D) carbon nanomateirlas from various biomass precursors via hydrothermal assisted synthesis. It offers a comprehensive discussion on the factors affecting the synthesis of 0D carbon nanomaterials, including precursor type, concentration, reaction temperature, and time. Furthermore, the review underscores the impact of different activation methods on the morphology and electrochemical performance of 0D carbon nanomaterials. Finally, we outline the challenges and future prospects of utilizing biomass-derived carbon nanomaterials in supercapacitor applications, emphasizing the importance of optimizing synthesis parameters to attain the desired material properties.

Exploring the gas sensing performances of O-functionalized TiVC MXene: mechanistic insights from computations

The detection of toxic gases remains a critical challenge for environmental safety, and MXenes have rapidly emerged as innovative materials for sensor development. In this work, we break new ground by exploring the sensing capabilities of O-functionalized TiVC MXene, a material not yet studied for gas sensing applications. Ab initio molecular dynamics (AIMD) simulations confirm the monolayer's dynamical stability at 300 K. Using first-principles-based DFT calculations, we systematically analyze the interaction of H2, CO, NO, NO2, and SO2 gas analytes with the TiVCO2 surface. Our study highlights key parameters such as adsorption strength, charge transfer, change in work function, and gas desorption time, critical to sensitivity and selectivity-core elements of the 4-S principle (sensitivity, selectivity, stability, and speed). The robust interaction energies (≤-48 kJ mol-1), short interaction distances, and significant charge transfer suggest that NO adsorption on TiVCO2 is characterized by strong physisorption, governed by hybridization of the 3d-orbitals of titanium and vanadium with the p-orbital of nitrogen. Notably, the change in work function upon interaction comes out to be >0.1 eV and the calculated desorption time of NO at 300 K is 1.74 s, making this MXene a highly promising candidate for NO gas detection at room temperature. Other gases exhibited much weaker physisorption with nanosecond desorption times, reinforcing the selective nature of TiVCO2 for NO detection. These findings offer insights into the use of O-functionalized TiVC MXene for gas sensors, with the potential to revolutionize the design of high-performance sensing devices in environmental monitoring and industrial applications.

Next-Generation Image Sensors Based on Low-Dimensional Semiconductor Materials

With the rapid advancement of technology of big data and artificial intelligence (AI), the exponential increase in visual information leads to heightened demands for the quality and analysis of imaging results, rendering traditional silicon-based image sensors inadequate. This review serves as a comprehensive overview of next-generation image sensors based on low-dimensional semiconductor materials encompassing 0D, 1D, 2D materials, and their hybrids. It offers an in-depth introduction to the distinctive properties exhibited by these materials and delves into the device structures tailored specifically for image sensor applications. The classification of novel image sensors based on low-dimensional materials, in particular for transition metal dichalcogenides (TMDs), covering the preparation methods and corresponding imaging characteristics, is explored. Furthermore, this review highlights the diverse applications of low-dimensional materials in next-generation image sensors, encompassing advanced imaging sensors, biomimetic vision sensors, and non-von Neumann imaging systems. Lastly, the challenges and opportunities encountered in the development of next-generation image sensors utilizing low-dimensional semiconductor materials, paving the way for further advancements in this rapidly evolving field, are proposed.

Recent Advances in Nanomaterial-Based Self-Healing Electrodes Towards Sensing and Energy Storage Applications

Nanomaterial-based self-healing electrodes have demonstrated significant potential in sensing and energy storage applications due to their ability to withstand electrical breakdowns at high electric fields. However, such electrodes often face mechanical challenges, such as cracking under stress, compromising stability and reliability. This review critically examines nanomaterial-based self-healing mechanisms, focusing on properties and applications in health monitoring, motion sensing, environmental monitoring, and energy storage. By comprehensively reviewing research conducted on dimension-based nanomaterials (OD, 1D, 2D, and 3D) for self-healing electrode applications, this paper aims to provide essential insights into design strategies and performance enhancements afforded by nanoscale dimensions. This review paper highlights the tremendous potential of harnessing dimensional nanomaterials to develop autonomously restoring electrodes for next-generation sensing and energy devices.

Mixed-Matrix Membrane-Based Piezoelectric CO2 Sensor with Self-Humidity Compensation

Monitoring the CO2 concentration is crucial for assessing respiratory illnesses in humans and safeguarding the environment. The ongoing difficulty lies in achieving highly sensitive detection while also eliminating the interference caused by humidity. There is an unmet need for portable sensors with both high sensitivity and good moisture resistance to monitor CO2 in real time. In this study, a novel sensor capable of capturing the piezoelectric signals induced by CO2 gas is developed. A quartz crystal microbalance (QCM) coated with a mixed- matrix membrane of metal-organic framework (MOF)/polyether block amide (Pebax) is designed as a transducer to detect CO2 at room temperature. The change in the concentration of CO2 can be detected by the frequency shift of the QCM sensor. The sensor shows an ultrahigh sensitivity of 371.8 Hz to 1000 ppm of CO2 because of the abundant polar group and nitrogen Lewis basic groups. Furthermore, the implementation of a self-humidity compensation algorithm significantly enhances the accuracy and reliability of CO2 concentration monitoring by effectively addressing the issue of humidity interference. Our research underscores the immense potential of MOF/Pebax QCM sensors with self-humidity compensation ability in the field of CO2 gas monitoring.

Universal Gas-Sensitive Detection of Various Lithium-Ion Battery Electrolyte Leakages via Ag@Ag2O-Functionalized SnO2 Nanoflowers with Abundant Oxygen Vacancies

Lithium-ion batteries (LIBs) provide many benefits, but trace electrolyte leakage can cause serious safety risks such as thermal runaway. Although gas sensors offer a potential solution, the complexity of electrolyte solvents in LIBs makes it challenging to develop sensing materials capable of universally detecting multiple solvent molecules. Here, Ag@Ag2O-functionalized SnO2 nanoflowers were synthesized using a self-template pyrolysis strategy for the sensitive detection of both common solvent molecules and widely used electrolytes. These sensors, enhanced by abundant oxygen vacancies introduced by Ag@Ag2O functionalization, exhibit excellent sensitivity, particularly to dimethyl carbonate, with a response of 106-100 ppm, a low detection limit of 11.76 ppb, and rapid response/recovery times (28/55 s) at an operating temperature of 200 °C. The sensor performance was validated by density functional theory calculations, which corroborated the effectiveness of the sensing material. In simulated LIB leakage scenarios, such as puncture and electrolyte injection, the sensors demonstrated quick responses to various common electrolyte compositions, indicating their potential for practical applications. This study highlights an effective method for fabricating composite sensing materials and emphasizes the practical significance of our universal detection approach for practical monitoring of electrolyte leakage in energy storage devices.

Selective sensing of NH3 and NO2 on WSe2 monolayers based on defect concentration regulation

Defect engineering is an important method to control material properties. In this paper, large-scale sampling density functional theory (DFT) was used to investigate the adsorption and sensing behavior of NH3 and NO2 on a WSe2 monolayer, with a focus on the effect of selenium vacancy concentration. The results demonstrate that selectivity is inhibited on a perfect monolayer due to the similar adsorption energy of the two gases, NH3 and NO2, while selectivity can be obtained for both of them under different selenium vacancy concentrations (NH3 about 2-5.6%, NO2 about >8.3%). It is believed that the good match between the unique surface structure of the double-color (double-charged) wave wheel disk-like structure of the WSe2 monolayer and the molecular structure of both of the two representative molecules, NH3 and NO2, contributes dominantly to the unusual performance. The results demonstrate that one kind of material-WSe2 monolayer-can perform selective sensing of both NH3 and NO2, respectively, using only defect adjustment. It is particularly important to acquire the selectivity to NH3 in the mixture of NO2 and NH3. It also provides opportunities for understanding materials and patterned catalyst design.

Toward the Optimization of a Perovskite-Based Room Temperature Ozone Sensor: A Multifaceted Approach in Pursuit of Sensitivity, Stability, and Understanding of Mechanism

Metal halide perovskites (MHPs) have attracted significant attention owing to their simple manufacturing process and unique optoelectronic properties. Their reversible electrical or optical property changes in response to oxidizing or reducing environments make them prospective materials for gas detection technologies. Despite advancements in perovskite-based sensor research, the mechanisms behind perovskite-gas interactions, vital for sensor performance, are still inconclusive. This work presents the first evaluation of the sensing performance and long-term stability of MHPs, considering factors such as halide composition variation and Mn doping levels. The research reveals a clear correlation between halide composition and sensing behavior, with Br-rich sensors displaying a p-type response to O3 gas, while Cl-rich counterparts exhibit n-type sensing behavior. Notably, Mn-doping significantly enhances O3 sensing performance by facilitating the gas adsorption process, as supported by both atomistic simulations and experimental evidence. Long-term evaluation of the sensors provides valuable insights into evolving sensing behaviors, highlighting the impact of dynamic instabilities over time. Overall, this research offers insights into optimal halide combination and Mn-doping levels, representing a significant step forward in engineering room temperature perovskite-based gas sensors that are not only low-cost and high-performing but also durable, marking a new era in sensor technology.

Low Power Gas Sensors: From Structure to Application

Gas sensors are pivotal across industries, encompassing environmental monitoring, industrial safety, and healthcare. Recently, a surge in demand for low power gas sensors has emerged, driven by the huge need for applications in portable devices, wireless sensor networks, and the Internet of things (IoT). The practical realization of a densely interconnected sensor network demands gas sensors to have low power consumption for energy-efficient operation. This Perspective offers a comprehensive overview of the progress of low-power sensors for gas and volatile organic compound detection, with a keen focus on the interplay between sensing materials (including metal oxide semiconductors, metal-organic frameworks, and two-dimensional materials), sensor structures, and power consumption. The main gas sensing mechanisms are discussed, and we delve into the mechanisms for achieving low power consumption including material properties and sensor design. Furthermore, typical applications of low power gas sensors are also presented, including wearable technology, food safety, and environmental monitoring. The review will end by discussing some open questions and ongoing needs.

Scientific Insights into the Quantum Dots (QDs)-Based Electrochemical Sensors for State-of-the-Art Applications

Size-dependent optical and electronic properties are unique characteristics of quantum dots (QDs). A significant advantage is the quantum confinement effect that allows their precise tuning to achieve required characteristics and behavior for the targeted applications. Regarding the aforementioned factors, QDs-based sensors have exhibited dramatic potential for the diverse and advanced applications. For example, QDs-based devices have been potentially utilized for bioimaging, drug delivery, cancer therapy, and environmental remediation. In recent years, use of QDs-based electrochemical sensors have been further extended in other areas like gas sensing, metal ion detection, monitoring of organic pollutants, and detection of radioactive isotopes. Objective of this study is to rationalize the QDs-based electrochemical sensors for state-of-the-art applications. This review article comprehensively illustrates the importance of aforementioned devices along with sources from which QDs devices have been formulated and fabricated. Other distinct features of QDs devices are associated with their extremely high active surfaces, inherent ability of reproducibility, sensitivity, and selectivity for the targeted analyte detection. In this review, major categories of QD materials along with justification of their key roles in electrochemical devices have been demonstrated and discussed. All categories have been evaluated with special emphasis on the advantages and drawbacks/challenges associated with QD materials. However, in the interests of readers and researchers, recent improvements also have been included and discussed. On the evaluation, it has been concluded that despite significant challenges, QDs-based electrochemical sensors exhibit excellent performances for state-of-the-art and targeted applications.

Pulse-Driven MEMS NO2 Sensors Based on Hierarchical In2O3 Nanostructures for Sensitive and Ultra-Low Power Detection

As the mainstream type of gas sensors, metal oxide semiconductor (MOS) gas sensors have garnered widespread attention due to their high sensitivity, fast response time, broad detection spectrum, long lifetime, low cost, and simple structure. However, the high power consumption due to the high operating temperature limits its application in some application scenarios such as mobile and wearable devices. At the same time, highly sensitive and low-power gas sensors are becoming more necessary and indispensable in response to the growth of the environmental problems and development of miniaturized sensing technologies. In this work, hierarchical indium oxide (In2O3) sensing materials were designed and the pulse-driven microelectromechanical system (MEMS) gas sensors were also fabricated. The hierarchical In2O3 assembled with the mass of nanosheets possess abundant accessible active sites. In addition, compared with the traditional direct current (DC) heating mode, the pulse-driven MEMS sensor appears to have the higher sensitivity for the detection of low-concentrations of nitrogen dioxide (NO2). The limit of detection (LOD) is as low as 100 ppb. It is worth mentioning that the average power consumption of the sensor is as low as 0.075 mW which is one three-hundredth of that in the DC heating mode. The enhanced sensing performances are attributed to loose and porous structures and the reducing desorption of the target gas driven by pulse heating. The combination of morphology design and pulse-driven strategy makes the MEMS sensors highly attractive for portable equipment and wearable devices.

Non-Invasive Diagnostic Approaches for Kidney Disease: The Role of Electronic Nose Systems

Kidney diseases are a group of conditions related to the functioning of kidneys, which are in turn unable to properly filter waste and excessive fluids from the blood, resulting in the presence of dangerous levels of electrolytes, fluids, and waste substances in the human body, possibly leading to significant health effects. At the same time, the toxins amassing in the organism can lead to significant changes in breath composition, resulting in halitosis with peculiar features like the popular ammonia breath. Starting from this evidence, scientists have started to work on systems that can detect the presence of kidney diseases using a minimally invasive approach, minimizing the burden to the individuals, albeit providing clinicians with useful information about the disease's presence or its main related features. The electronic nose (e-nose) is one of such tools, and its applications in this specific domain represent the core of the present review, performed on articles published in the last 20 years on humans to stay updated with the latest technological advancements, and conducted under the PRISMA guidelines. This review focuses not only on the chemical and physical principles of detection of such compounds (mainly ammonia), but also on the most popular data processing approaches adopted by the research community (mainly those relying on Machine Learning), to draw exhaustive conclusions about the state of the art and to figure out possible cues for future developments in the field.

Polyoxometalate Cluster-Guided Dynamic Nucleation and Hierarchical Growth of Branched WO3 Nanofibers with Ultrafine Pt Nanoparticles for Advanced Gas Sensing

In the food industry, 2,3-butanedione is a significant volatile organic compound valued for its unique aroma and flavor. Real-time detection of its concentration during food preparation is crucial for ensuring optimal taste and food safety. However, accurately detecting low concentrations of 2,3-butanedione requires highly sensitive sensing materials. Herein, we present a novel synthesis of branched WO3 nanofibers decorated with ultrafine Pt nanoparticles (Pt NPs-WO3 NFs), templated by polyoxometalate (POM) clusters, through a combination of electrospinning and thermal oxidation strategies for advanced gas sensing applications. This Pt NPs-WO3 NFs-based sensor exhibits impressive sensitivity (Ra/Rg = 2.25 vs 500 ppb), a low detection limit of 10 ppb, high selectivity, excellent repeatability, and stable performance over a period of 25 days. Using POM clusters as templates offers significant advantages over the traditional WCl6 salt in synthesizing WO3 NFs with smooth surfaces. Specifically, the POM clusters guide the dynamic nucleation and hierarchical growth of branched NFs, enhancing the concentration of oxygen vacancies and increasing the number of active adsorption sites. Furthermore, the uniform dispersion of ultrafine Pt NPs (≈ 4 nm) within the WO3 NFs further enhances the catalytic activation of 2,3-butanedione, significantly improving the gas sensing performance. This study introduces an efficient method to synthesize Pt NPs-WO3 NFs with potential for manufacturing advanced nanostructured sensing materials using POM clusters as templates, paving the way for high-performance gas sensing technologies.

Magnetic Field Assisted Enhanced Sensitivity of Nonferromagnetic Materials Boosting the Carrier Transfer: Mechanistic Studies

The performance of semiconductor sensors is determined by reaction kinetics, conductivity, and electron mobility, which are undoubtedly closely related to the electron motion behavior. Therefore, the effective regulation of electronic states is crucial for improving gas sensing properties. Previous methods of enhancing the gas-sensing performance have induced complex material modifications, and the extent of performance improvement is usually very limited. Further optimization of the gas sensing performance requires continuous efforts to advance new technologies. Toward this issue, a novel magnetic field-induced strategy is adopted to boost the carrier transfer efficiency of nonferromagnetic semiconductors. The gas sensing investigation results manifest that the applied magnetic field can effectively enhance the sensitivity and reduce the baseline resistance. The In2O3 NC-2 (In2O3 nanocubes) with an applied magnetic field have a greatly enhanced response of 161.4 toward 100 ppm formaldehyde, which is 2.5 times higher than that without magnetic field. The enhanced gas sensing properties can be mainly attributed to magnetization of reactive materials, which makes the orientation of electronic magnetic moments consistent, thus greatly contributing to reactivity. This work introduces a practical approach to effectively improve gas sensing performance without further morphology optimization, noble metal catalysis, structural modification, and material cladding. The results of this study provide new insights for designing novel gas sensors to improve the gas sensing performance.

Robust Treble-Weaving Wearable Textiles for Pressure and Temperature Monitoring in Harsh Environments

Wearable sensing textiles with continuous temperature monitoring, tactile feedback, and motion perception are highly desirable for personal safeguarding in extreme environments, such as fire scenes and extreme sports. However, it remains challenging for current wearable sensors to maintain reliable performance and provide point-of-care monitoring in harsh environments, such as high- and low-temperature or high-humidity conditions. Herein, a robust temperature and pressure sensing textile (TPST) with a hierarchical triple-weaving structure is developed using industrial weaving technology. The well-engineered interlacing configuration of the polyimide binding yarns in the triple-weaving structure tightly solidifies the carbon-based sensing yarns between two weaving layers, forming an integrated textile sensing array. The TPST not only exhibits excellent sensing sensitivity, reliability, and rapid response to pressure and temperature stimuli but also shows robust mechanical properties, flame resistance, and wearing comfort. Moreover, we demonstrate the application of the TPST for continuous temperature monitoring, human motion mapping, and vital sign monitoring. This technology offers significant potential for enhancing autonomous rescue operations and defense wearables.

Current Advances of CO Sensing Based on Low Dimensional Materials

Carbon monoxide (CO) is a harmful gas with significant impacts on human health and the environment. Its timely detection, especially in the event of thermal runaway in automotive lithium batteries, is crucial to prevent casualties. This paper reviews the progress in the development of efficient, sensitive, and reliable CO sensors, focusing on electrochemical, optical, and resistive sensing materials. Low-dimensional materials have a large specific surface area, providing an abundant number of active sites, which has drawn extensive attention from researchers. According to the different sensor signals, we categorized these sensors into electrical and optical signal sensors. We hope that by systematically introducing the sensing mechanism and sensing performance of these two kinds of sensors, appropriate CO sensors can be developed in different application scenarios so as to realize early warning and monitoring to the maximum extent, reduce industrial losses, and ensure the life and health of personnel.

Advancements in nanomaterials for nanosensors: a comprehensive review

Nanomaterials (NMs) exhibit unique properties that render them highly suitable for developing sensitive and selective nanosensors across various domains. This review aims to provide a comprehensive overview of nanomaterial-based nanosensors, highlighting their applications and the classification of frequently employed NMs to enhance sensitivity and selectivity. The review introduces various classifications of NMs commonly used in nanosensors, such as carbon-based NMs, metal-based NMs, and others, elucidating their exceptional properties, including high thermal and electrical conductivity, large surface area-to-volume ratio and good biocompatibility. A thorough examination of literature sources was conducted to gather information on NMs-based nanosensors' characteristics, properties, and fabrication methods and their application in diverse sectors such as healthcare, environmental monitoring, industrial processes, and security. Additionally, advanced applications incorporating machine learning techniques were analyzed to enhance the sensor's performance. This review advances the understanding and development of nanosensor technologies by providing insights into fabrication techniques, characterization methods, applications, and future outlook. Key challenges such as robustness, biocompatibility, and scalable manufacturing are also discussed, offering avenues for future research and development in this field.

Synergistic sensitization effects of single-atom gold and cerium dopants on mesoporous SnO2 nanospheres for enhanced volatile sulfur compound sensing

The real-time monitoring of volatile sulfur compounds is indispensable; however, it continues to pose a significant challenge due to issues such as limited performance towards parts-per-billion (ppb)-level gas. Herein, a concept of synergistic sensitization effects involving single-atom gold (Au) and cerium (Ce) dopants is proposed to boost the sensing performance of allyl mercaptan, a common volatile sulfur compound. As a proof-of-concept, a chemiresistive gas sensor based on mesoporous SnO2 nanospheres with single-atom Au decoration and Ce dopant (denoted Au/Ce-SnO2) is successfully synthesized. The synthesis of Au/Ce-SnO2 is achieved through the utilization of a self-template strategy, employing metal-phenolic hybrids as a precursor. The obtained materials exhibit high specific surface area (89.4 m2 g-1), and small particle size (∼86 nm). The gas sensor reveals unprecedented sensitivity (0.097 ppb-1) and ultra-low detection limit (0.74 ppb), surpassing all state-of-the-art allyl mercaptan gas sensors. Furthermore, a wireless gas sensor is constructed for highly selective and real-time monitoring of allyl mercaptan. The decoration of single-atom Au facilitates the adsorption and dissociation of oxygen and target gases. Simultaneously, the Ce dopant enhances the oxidation of allyl mercaptan. The sensing performance is boosted by the mesoporous framework of SnO2, as well as the synergistic sensitization effects resulting from single-atom Au decoration and Ce doping, thereby facilitating its potential application in environmental and health-related domains.

High versatility of polyethylene terephthalate (PET) waste for the development of batteries, biosensing and gas sensing devices

Continuously growing adoption of electronic devices in energy storage, human health and environmental monitoring systems increases demand for cost-effective, lightweight, comfortable, and highly efficient functional structures. In this regard, the recycling and reuse of polyethylene terephthalate (PET) waste in the aforementioned fields due to its excellent mechanical properties and chemical resistance is an effective solution to reduce plastic waste. Herein, we review recent advances in synthesis procedures and research studies on the integration of PET into energy storage (Li-ion batteries) and the detection of gaseous and biological species. The operating principles of such systems are described and the role of recycled PET for various types of architectures is discussed. Modifying the composition, crystallinity, surface porosity, and polar surface functional groups of PET are important factors for tuning its features as the active or substrate material in biological and gas sensors. The findings indicate that conceptually new pathways to the study are opened up for the effective application of recycled PET in the design of Li-ion batteries, as well as biochemical and catalytic detection systems. The current challenges in these fields are also presented with perspectives on the opportunities that may enable a circular economy in PET use.

Metal-Organic-Framework Derived Co-Mo Multimetal Oxide Semiconductors: Selective Trace-Level Hydrogen Sulfide Detection

The development of a highly selective and trace-level gas sensing platform for detecting hydrogen sulfide (H2S) remains a formidable challenge. To solve this problem, Co-Mo multimetal oxide semiconductors are rationally tailored by employing metal organic frameworks (MOFs) as self-sacrificial templates. The MOF-derived Co3O4/β-CoMoO4 based gas sensors displays high sensitivity (Rg/Ra = 22) to 10 ppm of H2S and ultralow limit of detection (10 ppb H2S). The formation of p-p heterojunction and multivalence states of Mo play a crucial role in electron transfer and oxygen adsorption. A sensor array constructed from four Co3O4/β-CoMoO4 materials with different Co/Mo ratios demonstrates a superior selective discrimination of H2S from other VOCs and malodorous gases by principal component analysis (PCA). Besides, a H2S gas sensing and alarming platform was designed for monitoring the environment contaminated with H2S. This finding provides a feasible approach for the discovery of highly efficient gas sensors to monitor environmental H2S concentration.

Modification strategies for semiconductor metal oxide nanomaterials applied to chemiresistive NOx gas sensors: A review

Semiconductor metal oxides (SMOs) nanomaterials are a category of sensing materials that are widely applied to chemiresistive NOx gas sensors. However, there is much space to improve the sensing performance of SMOs nanomaterials. Therefore, how to improve the sensing performance of SMOs nanomaterials for NOx gases has always attracted the interest of researchers. Up to now, there are few reviews focus on the modification strategies of SMOs which applied to NOx gas sensors. In order to compensate for the limitation, this review summarizes the existing modification strategies of SMOs, hoping to provide researchers a view of the research progress in this filed as comprehensive as possible. This review focuses on the progress of the modification of SMOs nanomaterials for chemiresistive NOx (NO, NO2) gas sensors, including the morphology modulation of SMOs, compositing SMOs, loading noble metals, doping metal ions, compositing with carbon nanomaterials, compositing with biomass template, and compositing with MXene, MOFs, conducting polymers. The mechanism of each strategy to enhance the NOx sensing performance of SMOs-based nanomaterials is also discussed and summarized. In addition, the limitations of some of the modification strategies and ways to address them are discussed. Finally, future perspectives for SMOs-based NOx gas sensors are also discussed.

Mechanism of Interfacial Molecular Interactions Reveals the Intrinsic Factors for the Highly Enhanced Sensing Performance of Ag-Loaded Co3O4

The noble metal-loaded strategy can effectively improve the gas-sensing performances of metal oxide sensors. However, the gas-solid interfacial interactions between noble metal-loaded sensing materials and gaseous species remain unclear, posing a significant challenge in correlating the physical and chemical processes during gas sensing. In this study, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ Raman spectroscopy were conducted to collaboratively investigate the interfacial interactions involved in the ethanol gas-sensing processes over Co3O4 and Ag-loaded Co3O4 sensors. In situ DRIFTS revealed differences in the compositions and quantities of sensing reaction products, as well as in the adsorption-desorption interactions of surface species, among Co3O4 and Ag-loaded Co3O4 materials. In parallel, in situ Raman spectroscopy demonstrated that the ethanol atmosphere can modulate the electron scattering of Ag-loaded Co3O4 materials but not of raw Co3O4. In situ experimental results revealed the intrinsic reason for the highly enhanced sensing performances of the Ag-loaded Co3O4 sensors toward ethanol gas, including a decreased optimal working temperature (from 250 to 150 °C), an improved gas response level (from 24 to 257), and accelerated gas recovery dynamics. This work provides an effective platform to investigate the interfacial interactions of sensing processes at the molecular level and further advances the development of high-performance gas sensors.

Sub-50 nm patterning of alloy thin films via nanophase separation for hydrogen gas sensing

A novel patterning method achieves two-dimensional nano-patterning of metal nanofibers by depositing a platinum-cerium alloy film on a silicon wafer and inducing phase separation in an oxygen-carbon monoxide atmosphere. The resulting nano-patterned thin film, Pt#CeO2/Si, consists of platinum and cerium oxide with an average pattern width of 50 nm and exhibits potential as a hydrogen sensor with sensitive electrical responses to hydrogen ad/desorption. The patterning method introduced herein addresses the challenge of wavelength limitations in traditional optical lithography, offering a scalable approach for sub-50 nm patterns, which are crucial for advanced sensor and electronic applications.

Preparation and NH3 gas-sensing properties of Ag/β-AgVO3 nanorods

NH3 gas sensors operating at room temperature, consisting of Ag nanoparticles decorated β-AgVO3 nanorods (Ag/β-AgVO3 NRs), were fabricated via a facile hydrothermal method without the need for a template. The surface characteristics and compositions of Ag/β-AgVO3 NRs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Ag nanoparticles, ranging in diameter from approximately 20 to 40 nm, were dispersed on the surface of monoclinic β-AgVO3 NRs with diameters ranging from 50 to 105 nm and lengths from 0.3 to 1.3 μm. The NH3 gas sensing properties of Ag/β-AgVO3 NRs were studied under both dry air and humid conditions at room temperature. Comparative analysis demonstrated that the Ag/β-AgVO3 NRs exhibited a strong response to NH3 gas under 70% relative humidity (RH) at room temperature compared to α-AgVO3 NRs. Specifically, the response of the Ag/β-AgVO3 NRs to 5 ppm NH3 increased by 2.25 times as the RH varied from 20% to 80% at room temperature. This enhanced response was attributed to the effects of formation of nanoheterojunctions, nano-metallic Ag activity and the conductivity of NH4+ and OH- ions induced by the presence of humidity. The room temperature NH3 gas sensors based on Ag/β-AgVO3 NRs demonstrated strong responses to low NH3 concentrations, high selectivity, good reproducibility, and long-term stability, and show promise for the development of low-power and cost-effective NH3 gas sensors for practical applications even under high humidity.

Advances in flame synthesis of nano-scale architectures for chemical, biomolecular, plasmonic, and light sensing

Flame spray pyrolysis (FSP), a key technique under the broader category of flame aerosol synthesis, is being increasingly explored for the design of advanced miniaturized sensor architectures with applications including chemical, biomolecular, plasmonic, and light sensing. This review provides an overview of the advantages of FSP for the fabrication of nanostructured materials for sensing, delving into synthesis strategies and material structures that meet the increasing demands for miniaturized sensor devices. We focus on the fundamentals of FSP, discussing reactor configurations and how process parameters such as precursor compositions, flow rates, and temperature influence nanoparticle characteristics and their sensing performance. A detailed analysis of nanostructures, compositions, and morphologies made by FSP and their applications in chemical, chemiresistive, plasmonic, biosensing, and light sensing is presented. This review identifies the challenges and opportunities of FSP, exploring current limitations and potential improvements for industrial translation. We conclude by highlighting future research directions aiming to establish guidelines for the flame-based design of nano-scale sensing architectures.

Nanostructure-based orbital angular momentum encryption and multiplexing

The orthogonality among the OAM modes provides a new degree of freedom for optical multiplexing communications. So far, traditional Dammann gratings and spatial light modulators (SLMs) have been widely used to generate OAM beams by modulating electromagnetic waves at each pixel. However, such architectures suffer from limitations in terms of having a resolution of only a few microns and the bulkiness of the entire optical system. With the rapid development of the electromagnetic theory and advanced nanofabrication methods, artificial nanostructures, especially optical metasurfaces, have been introduced which greatly shrink the size of OAM multiplexing devices while increasing the level of integration. This review focuses on the study of encryption, multiplexing and demultiplexing of OAM beams based on nanostructure platforms. After introducing the focusing characteristics of OAM beams, the interaction mechanism between OAM beams and nanostructures is discussed. The physical phenomena of helical dichroism response and spatial separation of OAM beams achieved through nanostructures, setting the stage for OAM encryption and multiplexing, are reviewed. Afterward, the further advancements and potential applications of nanophotonics-based OAM multiplexing are deliberated. Finally, the challenges of conventional design methods and dynamic tunable techniques for nanostructure-based OAM multiplexing technology are addressed.

Programmable and Modularized Gas Sensor Integrated by 3D Printing

The rapid advancement of intelligent manufacturing technology has enabled electronic equipment to achieve synergistic design and programmable optimization through computer-aided engineering. Three-dimensional (3D) printing, with the unique characteristics of near-net-shape forming and mold-free fabrication, serves as an effective medium for the materialization of digital designs into usable devices. This methodology is particularly applicable to gas sensors, where performance can be collaboratively optimized by the tailored design of each internal module including composition, microstructure, and architecture. Meanwhile, diverse 3D printing technologies can realize modularized fabrication according to the application requirements. The integration of artificial intelligence software systems further facilitates the output of precise and dependable signals. Simultaneously, the self-learning capabilities of the system also promote programmable optimization for the hardware, fostering continuous improvement of gas sensors for dynamic environments. This review investigates the latest studies on 3D-printed gas sensor devices and relevant components, elucidating the technical features and advantages of different 3D printing processes. A general testing framework for the performance evaluation of customized gas sensors is proposed. Additionally, it highlights the superiority and challenges of programmable and modularized gas sensors, providing a comprehensive reference for material adjustments, structure design, and process modifications for advanced gas sensor devices.

Effect of heterogenous dopant and high temperature pulse excitation on ozone sensing behavior of In2O3 nanostructures and an image recognition method coupled to ozone sensing array

Ground-level ozone (O3) is a primary air pollutant with potential adverse impacts on human health and ecosystems. Aiming to detect O3 concentration and develop efficient O3 sensing materials, sensing behavior of heterogenous cation (Fe3+, Sn4+ and Sb5+) doped In2O3 nanostructures was investigated. The incorporation of these cations modulated the electronic structure of semiconductor oxides, affecting the density of chemisorbed oxygen species and reactive sites. From O3 sensing results, Fe3+ doped In2O3 based sensors featuring saturated resistance curves in O3 gas, demonstrated fast sensing speed and qualified detection threshold (20 ppb). In contrast, Sn4+ and Sb5+ doped counterparts exhibited non-saturated sensing curves, resulting in slower response/recovery speed. As a proof-of-concept, these optimized sensors were integrated as the sensor array. Coupled to the image recognition technique, this sensor array could successfully discriminate O3 and NOx. That is, through the tailored combination of material modulation and sensor array, this study paves a novel approach for highly sensitive and selective O3 detection.

Janus HfSSe monolayer: a promising candidate for SO2and COCl2gas sensing

Janus monolayers based on transition metal dichalcogenides have garnered significant interest as potential materials for nano electronic device applications due to their exceptional physical and electronic properties. In this study, we investigate the stability of the Janus HfSSe monolayer usingab initiomolecular dynamics simulations and analyze the electronic properties in its pristine state. We then examine the impact of adsorbing toxic gas molecules (AsH3, COCl2, NH3, NO2, and SO2) on the monolayer's structure and electronic properties, testing their adsorption on different active sites on top of hafnium, selenium, and sulfur. The sensitivity of the gas molecules is quantified in terms of their adsorption energy, with the highest and lowest energies being observed for SO2(-0.278 eV) and NO2(-0.095 eV), respectively. Additionally, we calculate other properties such as recovery time, adsorption height, Bader charge, and charge difference density to determine the sensitivity and selectivity of the toxic gas molecules. Our findings suggest that the Janus HfSSe monolayer has the potential to function as SO2and COCl2gas sensor due to its high sensitivity for these two gases.

Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge-to-Edge Packing and Disrupts Cofacial Stacking

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge-to-edge tiling and face-to-face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge-to-edge contacts to reorder the stability of two surface-bound 2D polymorphs. The impact on dipole-enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short-range (3.4 Å) anti-parallel dipole contacts. Despite this situation, the reduction in self-association was attributed to long-range (~6.4 Å) dipolar repulsions between π-stacked macrocycles. This work highlights our ability to control the build-up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self-assembly.

Ce-Ag Active Bimetallic Pairs in Two-Dimensional SnS2 for Enhancing NO2 Sensing

Developing gas sensors capable of efficiently detecting harmful gases is urgent to protect the human environment. Here, an active Ce-Ag bimetallic pair was innovatively introduced into SnS2, which successfully exhibited excellent NO2 gas sensing performance. 0.8% Ce-SnS2-Ag showed a gas sensing response of 5.18 to 1 ppm of NO2 at a low temperature of 80 °C, with a lower limit of detection as low as 100 ppb. DFT calculations revealed that Ce atoms are substituted into the main lattice of SnS2, which opens up the interlayer spacing and serves as an anchor point to fix the Ag atoms in the interlayer. The Ce-Ag bimetallic pairs successfully modulate the electronic structure of SnS2, which promotes the adsorption and charge transfer between NO2 and Ce-SnS2-Ag and thus achieves such an outstanding gas sensing performance. This work opens an avenue for the rational functional modification of SnS2 with an optimized electronic structure and enhanced gas sensing.

New Advances in Antenna Design toward Wearable Devices Based on Nanomaterials

Wearable antennas have recently garnered significant attention due to their attractive properties and potential for creating lightweight, compact, low-cost, and multifunctional wireless communication systems. With the breakthrough progress in nanomaterial research, the use of lightweight materials has paved the way for the widespread application of wearable antennas. Compared with traditional metallic materials like copper, aluminum, and nickel, nanoscale entities including zero-dimensional (0-D) nanoparticles, one-dimensional (1-D) nanofibers or nanotubes, and two-dimensional (2-D) nanosheets exhibit superior physical, electrochemical, and performance characteristics. These properties significantly enhance the potential for constructing durable electronic composites. Furthermore, the antenna exhibits compact size and high deformation stability, accompanied by greater portability and wear resistance, owing to the high surface-to-volume ratio and flexibility of nanomaterials. This paper systematically discusses the latest advancements in wearable antennas based on 0-D, 1-D, and 2-D nanomaterials, providing a comprehensive overview of their development and future prospects in the field.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Gas nanosensors for health and safety applications in mining

The ever-increasing demand for accurate, miniaturized, and cost-effective gas sensing systems has eclipsed basic research across many disciplines. Along with the rapid progress in nanotechnology, the latest development in gas sensing technology is dominated by the incorporation of nanomaterials with different properties and structures. Such nanomaterials provide a variety of sensing interfaces operating on different principles ranging from chemiresistive and electrochemical to optical modules. Compared to thick film and bulk structures currently used for gas sensing, nanomaterials are advantageous in terms of surface-to-volume ratio, response time, and power consumption. However, designing nanostructured gas sensors for the marketplace requires understanding of key mechanisms in detecting certain gaseous analytes. Herein, we provide an overview of different sensing modules and nanomaterials under development for sensing critical gases in the mining industry, specifically for health and safety monitoring of mining workers. The interactions between target gas molecules and the sensing interface and strategies to tailor the gas sensing interfacial properties are highlighted throughout the review. Finally, challenges of existing nanomaterial-based sensing systems, directions for future studies, and conclusions are discussed.

In situ assembly of one-dimensional Pt@ZnO nanofibers driven by a ZIF-8 framework for achieving a high-performance acetone sensor

To obtain a high-performance gas sensor, it is essential to ingeniously design sensing materials containing the features of high catalytic performance, abundant oxygen vacancies, and splendid grain dispersibility through a simple method. Inspired by the fact that ZIF-8 contains semiconductor metal atoms, well-arranged ZnO nanoparticle (NP)-in situ assembled one-dimensional nanofibers (NFs) are obtained by one-step electrospinning. By incorporating Pt NPs into the cavity of ZIF-8 NPs, well-dispersed Pt@ZnO NPs driven by Pt@ZIF-8 composites are obtained after annealing. The well-arranged Pt@ZnO NP-assembled NFs not only exhibit abundant oxygen vacancies but also avoid the self-aggregation of ZnO and Pt NPs. Meanwhile, the small Pt NPs could improve the catalytic effect in return. Therefore, the gas sensor fabricated based on the above materials exhibits an acetone sensitivity of 6.1 at 370 °C, compared with pristine ZnO NFs (1.6, 5 ppm). Moreover, the well-arranged Pt@ZnO NP-assembled NFs show exceptional sensitivity to acetone with a 70.2 ppb-level detection limit in theory. The synergistic advantages of the designed sensing material open up new possibilities for non-invasive disease diagnosis.

Synthesis of Mesoporous Lanthanum-Doped SnO2 Spheres for Sensitive and Selective Detection of the Glutaraldehyde Disinfectant

Glutaraldehyde disinfectant has been widely applied in aquaculture, farming, and medical treatment. Excessive concentrations of glutaraldehyde in the environment can lead to serious health hazards. Therefore, it is extremely important to develop high-performance glutaraldehyde sensors with low cost, high sensitivity, rapid response, fabulous selectivity, and low limit of detection. Herein, mesoporous lanthanum (La) doped SnO2 spheres with high specific surface area (52-59 m2 g-1), uniform mesopores (with a pore size concentrated at 5.7 nm), and highly crystalline frameworks are designed to fabricate highly sensitive gas sensors toward gaseous glutaraldehyde. The mesoporous lanthanum-doped SnO2 spheres exhibit excellent glutaraldehyde-sensing performance, including high response (13.5@10 ppm), rapid response time (28 s), and extremely low detection limit of 0.16 ppm. The excellent sensing performance is ascribed to the high specific surface area, high contents of chemisorbed oxygen species, and lanthanum doping. DFT calculations suggest that lanthanum doping in the SnO2 lattice can effectively improve the adsorption energy toward glutaraldehyde compared to pure SnO2 materials. Moreover, the fabricated gas sensors can effectively detect commercial glutaraldehyde disinfectants, indicating a potential application in aquaculture, farming, and medical treatment.

Two-Dimensional Electrically Conductive Metal-Organic Frameworks as Chemiresistive Sensors

Metal-organic frameworks (MOFs) have emerged as attractive chemical sensing materials due to their exceptionally high porosity and chemical diversity. Nevertheless, the utilization of MOFs in chemiresistive type sensors has been hindered by their inherent limitation in electrical conductivity. The recent emergence of two-dimensional conductive MOFs (2D c-MOFs) has addressed this limitation by offering enhanced electrical conductivity, while still retaining the advantageous properties of MOFs. In particular, c-MOFs have shown promising advantages for the fabrication of sensors capable of operating at room temperature. Thus, active research on gas sensors utilizing c-MOFs is currently underway, focusing on enhancing sensitivity and selectivity. To comprehend the potential of MOFs as chemiresistive sensors for future applications, it is crucial to understand not only the fundamental properties of conductive MOFs but also the state-of-the-art works that contribute to improving their performance. This comprehensive review delves into the distinctive characteristics of 2D c-MOFs as a new class of chemiresistors, providing in-depth insights into their unique sensing properties. Furthermore, we discuss the proposed sensing mechanisms associated with 2D c-MOFs and provide a concise summary of the strategies employed to enhance the sensing performance of 2D c-MOFs. These strategies encompass a range of approaches, including the design of metal nodes and linkers, morphology control, and the synergistic use of composite materials. In addition, the review thoroughly explores the prospects of 2D c-MOFs as chemiresistors and elucidates their remarkable potential for further advancements. The insights presented in this review shed light on future directions and offer valuable opportunities in the chemical sensing research field.

Controlling the Morphology of Tellurene for a High-Performance H2S Chemiresistive Room-Temperature Gas Sensor

A two-dimensional (2D) van der Waals material composed only of tellurium (Te) atoms-tellurene-is drawing attention because of its high intrinsic electrical conductivity and strong interaction with gas molecules, which could allow the development of high-performance chemiresistive sensors. However, the correlation between the morphologies and gas detection properties of tellurene has not yet been studied in depth, and few reports exist on tellurene-based hydrogen sulfide (H2S) chemiresistive sensors in spite of their strong interaction with H2S molecules. Here, we investigate the morphology-dependent H2S gas detection properties of tellurene synthesized using a hydrothermal method. To tailor the morphologies of tellurene, the molecular weight of the surfactant was controlled, revealing that a 1D or 2D form was synthesized and also accompanied with the high crystallinity. The 1D tellurene-based chemiresistive sensor presented superior H2S detection properties compared to the 2D form, achieving a gas response (Rg/Ra) of ~38, even at room temperature. This outstanding performance was attributed to the high intrinsic electrical conductivity and high specific surface area of the resultant 1D tellurene.

Fabrication of conifer-like TiSnO2 nanorods for sensing H2S gas at room temperature

Conifer-like TiSnO2 nanorods mixed metal oxide was synthesized via the one-pot polyol method utilizing ethylene glycol (EG), poly(diallyldimethylammonium chloride) (PDDA), tin(II) chloride dihydrate (SnCl2·2H2O), and titanium(IV)-ethylhexanoate (TE) as precursor materials, aimed at room temperature H2S gas sensing. The effects of polyol duration time and capping agent concentration (PDDA) were examined to explore the morphological, structural, and gas-sensing characteristics, as well as to propose potential growth mechanisms of conifer-like TiSnO2 nanorods mixed metal oxide. The morphology and composition of the synthesized TiSnO2 mixed metal oxide were carried out employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffractometry (XRD). The experimental findings demonstrated a significant influence of polyol duration time and PDDA concentration on the morphological evolution of the synthesized TiSnO2 mixed metal oxide structures. Comparative gas-sensing analysis indicated that the conifer-like TiSnO2 nanorods mixed metal oxide exhibited the highest response (2.45%) towards H2S gas at a concentration of 1 ppm, along with a low detection limit (0.20 ppm) and good linearity (R2 = 0.9865) within the range of 1-15 ppm of H2S gas at room temperature.

Magnetic ε-Phosphorene for Sensing Greenhouse Gas Molecules

It is critical for gas sensors that sense greenhouse gas molecules to have both good sensitivity and selectivity for water molecules in the ambient environment. Here, we study the charge transfer, IV curves, and electric field tuning of vanadium-doped monolayer ϵ-phosphorene as a sensor for NO, NO₂, and H₂O gas molecules via first-principle and transport calculations. We find that the paramagnetic toxic molecules of NO and NO₂ have a high adsorption energy on V-ϵ-phosphorene, which originates from a large amount of charge transfer driven by the hybridisation of the localised spin states of the host with the molecular frontier orbital. Using the non-equilibrium Green's function, we investigate the IV responses with respect to the adsorption of different molecules to study the performance of gas molecule sensors. Our IV curves show a larger amount of changes in resistance of the paramagnetic NO and NO₂ than nonmagnetic H₂O gas molecules, suggesting both sensitivity and selectivity. Moreover, our calculations show that an applied external electric field (gate voltage) can effectively tune the amount of charge transfer. More charge transfer makes the sensor more sensitive to the molecule, while less charge transfer can reduce the adsorption energy and remove the adsorbed molecules, allowing for the repeated use of the sensor.

Metal-organic frameworks derived inverse/normal bimetallic spinel oxides toward the selective VOCs and H2S sensing

As the typical toxic and hazardous gases, volatile organic compounds (VOCs) and hydrogen sulfide (H₂S) pose a threat to the environment and human health. The demand for real-time detection of VOCs and H₂S gases is growing in many application to protect human health and air quality. Therefore, it is essential to develop advance sensing materials for the construction of effective and reliable gas sensors. Herein, bimetallic spinel ferrites with different metal ions (MFe₂O₄, M = Co, Ni, Cu and Zn) were designed by using metal-organic frameworks as templates. The evaluation of cation substitution on crystal structures (inverse/normal spinel structure) and electrical properties (n/p type and band gap) is systematically discussed. The results indicate that p-type NiFe₂O₄ and n-type CuFe₂O₄ nanocubes with inverse spinel structure exhibit high response and great selectivity towards acetone (C₃H₆O) and H₂S, respectively. Moreover, the two sensors also display the detection limits as low as 1 ppm (C₃H₆O) and 0.5 ppm (H₂S), which are far below the threshold values of 750 ppm to acetone and 10 ppm to H₂S for 8 h exposure set by American Conference of Governmental Industrial Hygienists (ACGIH). The finding provides new possibilities for the design of high-performance chemical sensors, which display tremendous potential for practical applications.

Flexible Room-Temperature Ammonia Gas Sensors Based on PANI-MWCNTs/PDMS Film for Breathing Analysis and Food Safety

Gas sensors have played a critical role in healthcare, atmospheric environmental monitoring, military applications and so on. In particular, flexible sensing devices are of great interest, benefitting from flexibility and wearability. However, developing flexible gas sensors with a high sensitivity, great stability and workability is still challenging. In this work, multi-walled carbon nanotubes (MWCNTs) were grown on polydimethylsiloxane (PDMS) films, which were further modified with polyaniline (PANI) using a simple chemical oxidation synthesis. The superior flexibility of the PANI-MWCNTs/PDMS film enabled a stable initial resistance value, even under bending conditions. The flexible sensor showed excellent NH₃ sensing performances, including a high response (11.8 ± 0.2 for 40 ppm of NH₃) and a low limit of detection (10 ppb) at room temperature. Moreover, the effect of a humid environment on the NH₃ sensing performances was investigated. The results show that the response of the sensor is enhanced under high humidity conditions because water molecules can promote the adsorption of NH₃ on the PANI-MWCNTs/PDMS films. In addition, the PANI-MWCNTs/PDMS film sensor had the abilities of detecting NH₃ in the simulated breath of patients with kidney disease and the freshness of shrimp. These above results reveal the potential application of the PANI-MWCNTs/PDMS sensor for monitoring NH₃ in human breath and food.

Candy-like heterojunction nanocomposite of WO3/Fe2O3-based semiconductor gas sensor for the detection of triethylamine

A highly efficient gas sensor for the detection of triethylamine based on candy-like WO₃/Fe₂O₃ nanocomposite was prepared. The control of morphology and sensing performance of n-n heterojunction WO₃/Fe₂O₃ nanocomposites were successfully achieved by the modulation of Fe element content. When the ratio of Fe to W is 0.4, the candy-like nanocomposite of WO₃/Fe₂O₃ with great performance is obtained. It is interesting that the candy-like nanocomposite of WO₃/Fe₂O₃ with a large specific surface area exhibits better selectivity and sensitivity for sensing TEA gases at a lower operating temperature (260 °C) compared with the gas sensor prepared by using WO₃ alone. To verify the feasibility, the sensing mechanism was investigated and real sample tests were conducted and discussed. Finally, a TEA gas sensor with low limit of detection, short response/recovery time (15/162 s), and high sensitivity was developed. In addition, the prepared gas sensor has satisfactory stability and selectivity and has practical application value.

Highly Sensitive Chemiresistive H2S Detection at Subzero Temperature over the Sb-Doped SnO2@g-C3N4 Heterojunctions under UV Illumination

NASA has detected H₂S in the persistently shadowed region of the lunar South Pole through NIR and UV/vis spectroscopy remotely, but in situ detection is generally considered to be more accurate and convincing. However, subzero temperatures in space drastically reduce chemisorbed oxygen ions for gas sensing reactions, making gas sensing at subzero temperature something that has rarely been attempted. Herein, we report an in situ semiconductor H₂S gas sensor assisted by UV illumination at subzero temperature. We constructed a g-C₃N₄ network to wrap the porous Sb doped SnO₂ microspheres to form type II heterojunctions, which facilitate the separation and transport of photoinduced charge carriers under UV irradiation. This UV-driven technique affords the gas sensor a fast response time of 14 s and a response value of 20.1 toward 2 ppm H₂S at -20 °C, realizing the sensitive response of the semiconductor gas sensor at subzero temperature for the first time. Both the experimental observations and theoretical calculation results provide evidence that UV irradiation and the formation of type II heterojunctions together promote the performance at subzero temperature. This work fills the gap of semiconductor gas sensors working at subzero temperature and suggests a feasible method for deep space gas detection.

Macroporous SnO2/MoS2 inverse opal hierarchitecture for highly efficient trace NO2 gas sensing

The innovation of NO₂ gas sensors is highly desirable in environmental monitoring and human safety. Herein, a macroporous SnO₂/MoS₂ inverse opal hierarchitecture has been constructed with substantial interface charge transfer, which realizes the efficient and stable detection of NO₂ with an enhanced response, fast kinetics, and high selectivity at low temperatures.

Recent Progress in Self-Powered Wireless Sensors and Systems Based on TENG

With the development of 5G, artificial intelligence, and the Internet of Things, diversified sensors (such as the signal acquisition module) have become more and more important in people's daily life. According to the extensive use of various distributed wireless sensors, powering them has become a big problem. Among all the powering methods, the self-powered sensor system based on triboelectric nanogenerators (TENGs) has shown its superiority. This review focuses on four major application areas of wireless sensors based on TENG, including environmental monitoring, human monitoring, industrial production, and daily life. The perspectives and outlook of the future development of self-powered wireless sensors are discussed.

Towards hospital-on-chip supported by 2D MXenes-based 5th generation intelligent biosensors

Existing public health emergencies due to fatal/infectious diseases such as coronavirus disease (COVID-19) and monkeypox have raised the paradigm of 5th generation portable intelligent and multifunctional biosensors embedded on a single chip. The state-of-the-art 5th generation biosensors are concerned with integrating advanced functional materials with controllable physicochemical attributes and optimal machine processability. In this direction, 2D metal carbides and nitrides (MXenes), owing to their enhanced effective surface area, tunable physicochemical properties, and rich surface functionalities, have shown promising performances in biosensing flatlands. Moreover, their hybridization with diversified nanomaterials caters to their associated challenges for the commercialization of stability due to restacking and oxidation. MXenes and its hybrid biosensors have demonstrated intelligent and lab-on-chip prospects for determining diverse biomarkers/pathogens related to fatal and infectious diseases. Recently, on-site detection has been clubbed with solution-on-chip MXenes by interfacing biosensors with modern-age technologies, including 5G communication, internet-of-medical-things (IoMT), artificial intelligence (AI), and data clouding to progress toward hospital-on-chip (HOC) modules. This review comprehensively summarizes the state-of-the-art MXene fabrication, advancements in physicochemical properties to architect biosensors, and the progress of MXene-based lab-on-chip biosensors toward HOC solutions. Besides, it discusses sustainable aspects, practical challenges and alternative solutions associated with these modules to develop personalized and remote healthcare solutions for every individual in the world.

Study on the Deterioration Mechanism of Pb on TiO2 Oxygen Sensor

Previous studies have shown that the pollutants in exhaust gas can cause performance deterioration in air-fuel oxygen sensors. Although the content of Pb in fuel oil is as low as 5 mg/L, the effect of long-term Pb accumulation on TiO2 oxygen sensors is still unclear. In this paper, the influence mechanism of Pb-containing additives in automobile exhaust gas on the response characteristics of TiO2 oxygen sensors was simulated and studied by depositing Pb-containing pollutants on the surface of a TiO2 sensitive film. It was found that the accumulation of Pb changed the surface gas adsorption state and reduced the activation energy of TiO2, thus affecting the steady-state response voltage and response speed of the TiO2-based oxygen sensor.

Current Trends in Nanomaterials for Metal Oxide-Based Conductometric Gas Sensors: Advantages and Limitations-Part 2: Porous 2D Nanomaterials

This article discusses the features of the synthesis and application of porous two-dimensional nanomaterials in developing conductometric gas sensors based on metal oxides. It is concluded that using porous 2D nanomaterials and 3D structures based on them is a promising approach to improving the parameters of gas sensors, such as sensitivity and the rate of response. The limitations that may arise when using 2D structures in gas sensors intended for the sensor market are considered.