Search Results (140)

Underground coal mining operations remain significantly threatened by the accumulation of methane (CH₄) and carbon monoxide (CO): Methane poses an acute explosion risk, and carbon monoxide serves as a critical biomarker for spontaneous coal combustion. Consequently, rigorous real-time monitoring to ensure environmental safety is necessitated, which is based on superior gas sensor devices. Although various detection modalities exist, conventional methods are frequently constrained by environmental sensitivity and limitations regarding long-term sensor stability. This review provides a comprehensive analysis of recent advancements in chemiresistive gas sensors based on metal oxide (MO) semiconductor materials with low cost, high stability, high sensitivity, and easy preparation, which are engineered for the detection of methane and carbon monoxide in coal mining environments. This study examines the redox-sensing mechanisms of both n-type and p-type MO semiconductors, for which special attention is directed toward optimization strategies designed to overcome the high activation energy of methane and improve carbon monoxide response kinetics. Importantly, novel approaches to lower high operating temperatures and improve the selectivity of MO sensors under complex mine environments have been comprehensively discussed. Full article

Benzene, toluene, and xylene (BTX) gases pose severe threats to public health on account of their toxic, carcinogenic properties and environmental recalcitrance. In addition, their similar molecular structures and chemical inertness complicate the practical quantification of BTX, severely hindering their high-selectivity detection. In this work, a chemiresistive sensor based on F-doped In₂O₃ nanofibers was constructed. This strategy successfully enhanced the sensor response values toward benzene, toluene, and xylene by approximately 4.3, 4.5, and 4.2 times, respectively. Meanwhile, the limits of detection were reduced from 1, 0.5, and 0.25 ppm to 0.5, 0.25 and 0.05 ppm, respectively. The theoretical lower detection limits for benzene, toluene, and xylene are as low as 9.9 ppb, 5.7 ppb, and 2.5 ppb, respectively. Machine learning methods were further employed for the identification of BTX gases and their binary mixtures. By capturing the distinctive and reproducible patterns of feature vectors from various analytes, the optimal algorithm established decision boundaries and achieved a classification accuracy of 92.1%. Meanwhile, the reasons for the improved gas sensing performance are discussed. Furthermore, a portable wireless gas sensing module based on F-doped In₂O₃ nanofibers was developed, which can be applied for detecting BTX. Full article

Triethylamine (TEA) is a common industrial contaminant and an important indicator of seafood spoilage. Therefore, determination of rapid and selective TEA is of great significance. This review article critically compares tungsten oxide (WO₃)- and molybdenum oxide (MoO₃)-based chemiresistive sensors by relating their crystal structure, surface chemistry, defect states, morphology, and interfacial electronic properties to TEA-sensing performance. Pristine WO₃- and MoO₃-based sensors generally operate at approximately 133–325 °C and provide sub-ppm detection, whereas doping, noble-metal sensitization, heterojunction formation, and light activation can reduce the operating temperature to 100–180 °C and extend detection into the low-ppb range. WO₃-based sensors have exhibited a response of 1100 to 20 ppm TEA at 160 °C, with an estimated detection limit of 5 ppb, whereas modified MoO₃-based sensors have also achieved decent detection limit of 1.7 ppb. WO₃ is particularly responsive to phase, facet, work-function, and catalytic-interface engineering, whereas α-MoO₃ benefits from its anisotropic structure, variable Mo valence, and favorable Lewis acid–base interactions with amines. Noble metals enhance gas sensing through catalytic and electronic sensitization, dopants regulate adsorption and defect chemistry, and n-n or p-n heterojunctions amplify resistance changes through depletion-layer modulation. Despite considerable advances in sensitivity, humidity interference, high power consumption, slow recovery, baseline drift, and limited long term stability remain unresolved. Future advances may require standardized performance assessment, operando mechanistic studies, humidity-resistant low-power devices, and validation under realistic seafood-storage and industrial conditions. Full article

Food spoilage along the supply chain represents a major global challenge, contributing to economic losses, environmental impacts, and food safety concerns. Graphene-based materials have emerged as promising platforms for real-time food freshness monitoring owing to their high surface area, electrical conductivity, chemical sensitivity, and compatibility with flexible sensing architectures. This review critically examines graphene-based sensing strategies for food freshness and spoilage monitoring, including chemiresistive, dielectric, field-effect, optical/fluorescence, photoelectrochemical, mass-sensitive, and colorimetric approaches. Representative sensing platforms are compared in terms of analytical performance, including detection range, limit of detection, selectivity, response and recovery times, calibration, reproducibility, and stability. Particular attention is given to machine-learning-assisted sensing, multifunctional platforms for temperature, humidity, and gas monitoring, and the challenges associated with real-world implementation, including environmental interference, sensor fouling, signal drift, long-term stability, and cross-matrix validation. Finally, commercialization readiness, integration into intelligent packaging, and safety and regulatory considerations related to graphene-based food-contact applications are discussed. Overall, the review identifies the main technological gaps and future research priorities toward robust, scalable, and practical graphene-based systems for real-time food freshness monitoring. Full article

Hydrogen (H₂) detection under practical operating conditions requires sensing materials that simultaneously provide accessible reaction sites, efficient gas diffusion pathways, and fast interfacial charge transfer. Here, a hierarchical star-sphere ZnCo₂O₄ (ZC) architecture was integrated with graphene oxide (GO) and Pt supported on graphitized carbon (Pt/C) to develop hybrid chemiresistive sensing layers for low-temperature hydrogen detection. The synthesized ZC-based material exhibited a hierarchical morphology consisting of porous microspheres and star-shaped assemblies, providing a multiscale framework for gas access and surface reactions. By varying the GO content from 0.1 to 1 wt% at a fixed Pt/C loading, the ZC-0.5G composite achieved the most balanced structure, with well-distributed GO sheets, preserved star–sphere morphology, the highest specific surface area (53.6 m²/g), and the largest pore volume (0.09 cm³/g). The optimized sensor gave responses of 12.96%, 19.20%, 22.87%, and 26.43% for 500, 4000, 8000 and 10,000 ppm H₂ concentrations, respectively, with measurable response down to 50 ppm. The highest sensing performance was achieved at 50 °C and 60% relative humidity (RH), where the hierarchical oxide framework, GO-assisted interfacial pathways, and Pt catalytic sites acted in concert. The sensor also showed repeatable cyclic behavior and preferential response to H₂ compared to methanol, isopropanol, ethanol, acetone, and dimethylformamide. The improved sensing performance is attributed to the synergistic combination of the hierarchical ZC framework, GO-assisted interfacial pathways, and Pt-assisted catalytic activation, which together facilitate gas diffusion, surface reactions, and resistance modulation. Full article

Strict monitoring of methane (CH₄) during underground coal mining is necessary, as the lower explosive limit (LEL) is 5 vol% in air. A conventional tin oxide (SnO₂)-based metal–oxide semiconductor (MOS) sensor has an operating temperature of 200–400 °C, which requires a prohibitive power demand and entails the risk of ignition within an intrinsically safe environment. The decoration of SnO₂ nanoarchitectures with palladium has been demonstrated to achieve room temperature (RT) detection of CH₄ due to the chemical sensitisation spillover mechanism and electronic sensitisation by Schottky barrier modulation. Moreover, palladisation of SnO₂ nanowires (NWs) is likely to be an effective route for achieving a more efficient detection of CH₄ aerosol at RT or near RT. The purpose of this mini-review is to provide a critical synthesis of advances that have been reported between 2020 and 2026. Because no published study to date has directly demonstrated room-temperature CH₄ detection using pure Pd-decorated SnO₂ nanowires, performance data from mechanistically analogous systems—namely H₂-sensing Pd–SnO₂ nanowires and CH₄-sensing non-nanowire Pd–SnO₂ nanostructures—are included in this review and are explicitly labelled as such throughout. This absence of direct RT CH₄ NW data constitutes the primary research gap motivating this review. The performance of Pd-containing SnO₂ nanostructures reported in the literature spans response values of 17.6 (300 ppm CH₄, 2.5 mol% Pd–SnO₂ nanoporous, 340 °C) to 21.3 (3000 ppm CH₄, bimetallic Pt–Pd–SnO₂ mesoporous, 400 °C), representing a 3–10× improvement over bare SnO₂ (response: 2–10 in the same concentration range). These benchmarks were obtained at elevated temperatures (340–400 °C); no equivalent room-temperature CH₄ detection data for Pd–SnO₂ nanowires currently exists in the published literature. Reported response times range from 3 to 9 s at elevated temperature (340–400 °C) to 74–78 s for room-temperature visible-light-activated systems, where photocatalytic oxygen activation is the rate-limiting step. The 30 s MSHA alarm threshold is met by elevated-temperature systems but remains a challenge for RT configurations. The LODs were 175.9 ppb (bimetallic PdxPt/SnO₂ mesoporous system). Two hybrid composites containing rGO exhibited an extended capability for RT operation. Bimetallic PdPt decoration and ML-augmented sensor arrays are identified as the most promising near-term pathways to bridge the selectivity and stability gaps for certified mining deployment. Full article

Listeria monocytogenes (LM), one of the most virulent foodborne pathogens, poses a serious threat to public health due to its strong environmental adaptability and high pathogenicity. Rapid, sensitive, and real-time detection of LM is of great importance. Chemiresistive gas sensors have attracted enormous attention in LM detection owing to their advantages of low cost, simple structure, fast response, and easy miniaturization, which can achieve indirect detection of LM by recognizing its specific metabolic volatile organic compounds. This review summarizes the recent progress in chemiresistive gas sensors for the detection of LM metabolites. First, the metabolic characteristics of LM and the typical volatile organic compound (3-hydroxy-2-butanone) as its characteristic biomarker are introduced. Then, the performance and sensing mechanisms of different types of chemiresistive gas sensors for LM metabolite detection are summarized and elaborated systematically. The application of chemiresistive gas sensors for the detection of actual samples and the progress in the design of related detection devices are introduced. Finally, the current challenges faced by chemiresistive gas sensors in LM metabolite detection and their future development prospects are discussed. This review provides a comprehensive reference for the research and practical application of chemiresistive gas sensors in Listeria monocytogenes detection. Full article

Recent demand for reliable, low-power, and cost-effective gas sensors has spurred research into chemiresistive materials that operate under ambient conditions. PEDOT and PEDOT:PSS combined with semiconductor metal oxides (SMOs) have attracted attention due to their complementary properties: polymer flexibility and stability, alongside oxide reactivity and robustness. This review highlights the integration of PEDOT and PEDOT:PSS with n- and p-type SMOs, concentrating on fabrication techniques, sensing mechanisms, and performance indicators, such as sensitivity, selectivity, and response time. Emphasis is placed on heterojunction engineering, morphology control, and the influence of particle size and environmental factors. Despite notable progress, challenges persist in long-term stability, selectivity in mixed gases, and performance under varying conditions. Interface engineering and composite optimisation show promise, with potential applications in environmental monitoring, industrial safety, and wearable diagnostics. Full article

Al-doped zinc oxide (AZO) thin films were deposited by RF magnetron sputtering using a simple doping approach: aluminum tape was placed directly on the ZnO target. The work focused on understanding how Al incorporation, annealing temperature, and annealing atmosphere affect the structural and electrical behavior of the films, particularly their baseline resistance for gas sensing applications. EDX measurements confirmed that increasing the Al-covered area on the target progressively increased the Al concentration in the deposited layers. XRD analysis showed that higher Al contents and stronger thermal treatments reduced crystallinity and promoted the formation of smaller crystallites. The electrical response changed markedly with both Al incorporation and thermal treatment. Pure ZnO films initially exhibited very high resistance, while annealing reduced it by several orders of magnitude. Further increasing the Al concentration improved conductivity due to the donor effect of Al in the ZnO lattice. Overall, the results show that RF sputtering and post-treatment strategies can provide broad control over the electrical resistance of ZnO-based thin films. This tunability makes AZO coatings attractive for adapting chemoresistive gas sensors to different sensing environments and operating regimes, and deposition and thermal treatment parameters determine the resistance range. Full article

High-sensitivity detection of formaldehyde is critically important for environmental protection and public health. Zinc oxide (ZnO) is a widely used core material for chemiresistive gas sensors; however, its conventional low-index facets suffer from a limited number of active sites, creating a bottleneck for further sensitivity enhancement. To overcome this limitation, this study pioneers the application of the highly reactive ZnO $\left[20\overline{2}1\right]$ high-index polar surface for formaldehyde detection. By leveraging its unique stepped atomic configuration and unprecedented density of coordination-unsaturated active sites, we systematically investigate the formaldehyde adsorption behavior and the underlying sensing mechanism using first-principles calculations based on density functional theory (DFT). The pristine ZnO $\left[20\overline{2}1\right]$ surface exhibits intrinsic metallic character. At a coverage of 1 monolayer (ML), the most stable G1 configuration achieves an adsorption energy of −1.54 eV per CH₂O molecule. Within a 2 × 1 supercell, formaldehyde adopts both associative and dissociative adsorption modes. At a lower coverage, formaldehyde forms a stable bidentate structure through dual C–O and Zn–O bonding interactions. Electronic structure analysis reveals significant orbital hybridization and interfacial charge redistribution upon adsorption. Notably, associative adsorption opens a bandgap of 0.04 eV at the Fermi level, inducing a metal-to-semiconductor transition. In contrast, dissociative adsorption results in pronounced n-type doping, thereby elucidating the microscopic origin of the resistivity decrease observed in ZnO-based sensors. Overall, this work highlights the structural advantages of high-index facets and demonstrates for the first time the superior formaldehyde adsorption capability of the ZnO $\left[20\overline{2}1\right]$ facet, providing robust theoretical guidance for the rational design of next-generation, high-performance gas-sensing materials. Full article

Transforming existing structural surfaces into sensing interfaces offers a promising route for scalable hydrogen monitoring in hydrogen-handling facilities, where leakage poses significant safety risks, addressing the limitations of conventional point-based sensors. In this study, a surface-integrated ZnFe₂O₄–CNT (ZFC) composite coating is developed as a potentially retrofit-compatible sensing solution to enable hydrogen sensing directly on cementitious materials, combining material-level functionality with data-driven concentration prediction. The ZFC composite was synthesized via a hydrothermal method followed by CNT functionalization and composite formation, and was then applied onto cement-based substrates using a thickness-controlled coating approach. Structural and morphological characterization (XRD, FESEM, TEM, BET) confirmed the formation of a hierarchical, porous architecture, while hydrogen sensing performance was evaluated under controlled thermo-hygrometric conditions (24–72 °C, 32–87% RH) at 10,000 ppm H₂. The sensor exhibited stable and reversible responses, with optimal performance at 39–52 °C and a minimum response time of 18 s. An XGBoost model enabled accurate prediction of hydrogen concentration, achieving R² ≈ 0.92 and RMSE ≈ 820 ppm under dynamic exposure. These results demonstrate that coupling redox-active oxide surfaces with conductive CNT networks enables effective surface-based chemiresistive sensing under realistic conditions. The proposed system transforms conventional cementitious materials into smart, surface-integrated hydrogen sensing systems, offering a scalable and retrofit-compatible approach for real-time monitoring in hydrogen-related infrastructure. Full article

The growing demand for reliable, real-time detection of ammonia (NH₃) has accelerated the development of chemiresistive gas sensors, while conventional semiconductors employed as sensing materials in chemiresistive sensors remain constrained by limited selectivity and high operating temperatures (typically 200–400 °C). Among the emerging porous materials, metal–organic frameworks (MOFs) have attracted significant attention as room-temperature NH₃ sensing materials owing to their structural tunability, enabling precise control over pore chemistry, functionality, and metal centers. However, a comprehensive study specifically focused on MOF-based chemiresistive NH₃ sensors operating at room temperature remains limited. This review critically targets the investigation of pristine MOFs, conductive MOFs, and MOF-based composites for NH₃ sensing, with an emphasis on sensing mechanisms, structure–property–performance relationships, stability, selectivity, and environmental effects. Furthermore, rational design strategies and prospects are discussed to provide guidelines for the development of next-generation high-performance room-temperature NH₃ chemiresistive sensors. Full article

Monitoring air quality is crucial for understanding and improving public health. There is interest in developing ultra-sensitive, low-power, cost-effective sensors. This work demonstrates that structural modulation of Sn nanoparticles through controlled deposition and oxidation enables a transition from metallic to semiconducting percolative networks, significantly enhancing NO₂ sensing performance at room temperature. The proposed percolation-driven sensing mechanism provides a new framework for understanding charge transport and gas interaction in nanostructured metal oxide systems. The nanoparticles are deposited near the percolation threshold for electrical conduction and, upon exposure to air, consist of a tin core and an amorphous Sn₃O₄ surface. Post-deposition heating in air at 320 °C for two hours forms SnO and Sn₃O₄ on top of the gold electrodes and polycrystalline SnO in the tetragonal litharge phase, known as Romarchite, on the glass between the electrodes. Both as-deposited and heat-treated sensors were capable of detecting NO₂ at room temperature, with a limit of detection in the parts-per-billion range. A percolation model is used to explain their operating currents, in which NO₂ reacts at nanoparticle gaps and intra-grain boundaries to form charge-depletion regions that primarily determine their resistance. Heat treatment has also been found to cause disproportionation of SnO, resulting in tin-rich precipitates and increasing the operating current to the milliampere range. These precipitates, although oxidized on their surfaces when exposed to air, may serve as bridges that reduce the total resistance of the percolating paths. Full article

A chemiresistive nitric oxide (NO) gas sensor based on Pt/WO₃ co-decorated carbon nanofibers (CNFs) was fabricated using a simple and scalable electrospinning process. This sensor demonstrates high-ppb-level NO detection at room temperature (25 °C), with an experimentally demonstrated detection limit of 100 ppb. It exhibits rapid response, good signal repeatability, excellent batch-to-batch reproducibility, and high selectivity toward NO. Compared with previously reported NO sensors, this work highlights the integration of Pt and WO₃ within a conductive CNF network, enabling room-temperature NO detection down to 100 ppb using a simple chemiresistive architecture. In addition, preliminary sensing tests were conducted using dried simulated breath samples prepared by introducing exogenous NO into exhaled breath from healthy volunteers, demonstrating the sensor’s capability to resolve different NO levels in a complex breath-related background. Owing to its reliable performance and cost-effective fabrication, the sensor holds potential as a NO sensing platform, providing a materials-level basis for future breath NO analysis and other related applications. Full article

The detection of trace nitrogen dioxide (NO₂) is critical for environmental monitoring and industrial safety. Among various sensing technologies, chemiresistive sensors based on semiconducting metal oxides are prominent due to their high sensitivity and fast response. However, their application is hindered by inherent limitations, including low selectivity and elevated operating temperatures, which increase power consumption. Two-dimensional metal oxysulfides have recently attracted attention as room-temperature sensing materials due to their unique electronic properties and fully reversible sensing performance. Meanwhile, their combination with optoelectronic gas sensing has emerged as a promising solution, combining higher efficiency with minimal energy requirements. In this work, we introduce non-layered 2D indium oxysulfide (In₂S_xO_3−x) synthesized via a two-step process: liquid metal printing of indium followed by thermal annealing of the resulting In₂O₃ in a H₂S atmosphere at 300 °C. The synthesized material is characterized by a micrometer-scale lateral dimension with 6.3 nm thickness and remaining n-type semiconducting behavior with a bandgap of 2.53 eV. It demonstrates a significant response factor of 1.2 toward 10 ppm NO₂ under blue light illumination at room temperature. The sensor exhibits a linear response across a low concentration range of 0.1 to 10 ppm, alongside greatly improved reversibility, selectivity, and sensitivity. This study successfully optimizes the application of 2D metal oxysulfide and presents its potential for the development of energy-efficient NO₂ sensing systems. Full article