To enhance gas sensor performance, this study addresses the high power consumption and temperature field non-uniformity issues in MEMS microheaters. A cantilevered membrane structure was designed to improve thermal isolation, whilst COMSOL Multiphysics multi-physics simulation was employed to optimise the geometric parameters of the support beams and heating zone. The research aims to achieve low power consumption, rapid heating, and a uniform, stable temperature distribution, thereby providing an ideal operating platform for metal oxide gas-sensitive materials and advancing the development of high-performance gas sensor.

Room-temperature detection of hydrazine (N2H4) remains challenging due to the limited sensitivity of conventional sensing materials. Herein, a ternary PANI/Au-ZnO nanoflower (NF) composite was developed via a facile wet-chemical method for room-temperature N2H4 sensing. The optimized PANI/Au-to-ZnO sensor (2:1) exhibited a remarkable response of 125% toward 30 ppm N2H4, along with rapid response/recovery characteristics (172s/68s toward 6 ppm N2H4), excellent long-term stability over five weeks, a low detection limit of 287.4 ppb, and outstanding selectivity. The enhanced sensing performance is attributed to the synergistic effects of oxygen vacancy-mediated adsorption enhancement and heterointerfacial charge-transfer amplification, which promote oxygen adsorption and interfacial charge transfer during N2H4 sensing. This work provides an effective strategy for developing room-temperature N2H4 sensors through heterostructure engineering.

In current research, In2O3 is widely used as n-type semiconductor gas sensing materials for detecting toxic and hazardous gases. However, In2O3 sensors still have disadvantages such as high working temperature and low response value. To address these challenges, Pr-Ag co-doped porous nanonest like In2O3 was prepared by adjusting the doping molar ratio of Pr and Ag using a hydrothermal method. This sensor exhibits excellent methanol gas sensing properties, including a high gas response value of 21.6 (10 ppm), fast gas adsorption and desorption equilibrium (10 s/9 s), and a low operating temperature (175 degrees C). The enhanced sensing mechanism was clarified through a combination of experiments and first-principles calculations. The results showed that after the co-doping of Pr and Ag, there was a higher adsorption energy, a narrower band gap, and a larger specific surface area, which significantly improved the gas sensing performance. The present work work open up a path for more accurate and better detection of methanol concentrations in industrial environments.

Non-invasive breath acetone analysis offers a promising approach for continuous diabetes monitoring. However, poor long-term stability and material-electrode interfacial drift in p-type metal oxide sensors remain key bottlenecks for their clinical translation. To address these challenges, a Micro-Electro-Mechanical-System (MEMS) acetone sensor was developed via the in-situ growth of Pt-doped NiO nanowalls on a micro-heater chip. Unlike conventional surface modification and physical coating methods, the intrinsic doping of Pt within the NiO lattice and its integration with the substrate address signal drift through a synergistic dual mechanism. Specifically, the in-situ growth minimizes contact resistance drift at the material-electrode interface. Simultaneously, intrinsic Pt lattice doping anchors the active sites, suppressing catalyst thermal agglomeration and preserving structural stability at the gas-solid interface. The optimized sensor exhibits a response of 10.3 to 100 ppm acetone at 200 °C (a 5.7-fold enhancement over pure NiO) and a response time of 37 s. Furthermore, the device demonstrates continuous stability over 60 days and steady-state reliability at the 1.8 ppm clinical diagnostic threshold. It also shows stable moisture resistance (up to 98% relative humidity), maintaining typical p-type characteristics without response reversal phenomena. Supported by competitive co-adsorption density functional theory (DFT) calculations, this moisture tolerance is attributed to a favorable adsorption energy that prioritizes acetone chemisorption over water molecules. Comprehensive characterizations and DFT models indicate that Pt doping triggers localized lattice distortions and charge compensation, increasing the surface oxygen vacancy concentration (35.2%). This theoretically broadens the hole accumulation layer (HAL) and facilitates single-molecule acetone adsorption (−1.12 eV), stabilizing the p-type conduction mechanism. This work provides a stable, drift-resistant acetone sensor capable of sub-ppm trace detection for non-invasive diabetes screening.

TiO2 nanomaterials are widely applied for the detection of harmful H2S gas due to their good electron mobility, relatively wide band gap (3–3.35 eV) and excellent thermal stability. However, H2S gas sensors still face challenges such as inferior response values and slow response dynamics. Herein, vertical aligned porous corn like TiO2 nanorod arrays are prepared in situ on the fluorine doped tin dioxide (FTO) using hydrothermal method. The gas sensing performance shows that the vertical aligned corn like TiO2 nanorod arrays exhibit outstanding gas sensing performance to 5 ppm H2S gas with UV illumination at 200℃, including excellent gas response (Ra/Rg =3.6), fast response/recovery time (12 s/33 s). This work provides novel gas sensing materials for the development of high performance H2S gas sensors.

Vertical oriented graphdiyne (GDY) nanowalls with unique hierarchical porous structure hold great promise in room-temperature gas sensors owing to their naturally adjustable bandgap and excellent conductivity. However, large response time and low response value remain a great challenge in view of the chemical inertness of carbon skeleton. Herein, uniform Pt nanoparticles anchored on GDY nanowalls are developed. The Pt/GDY sensor has an enhanced sensing performance compared to the GDY sensor, with a sensing response value of up to 52% and a response time of down to 24 s for 100 ppm NO2 at room temperature. The sensing mechanism is attributed to the bonding of sp-hybridized carbon in GDY with Pt, which significantly facilitates the charge transfer and activation adsorption of NO2 molecules. This is further elucidated by in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations. This study opens up a new surface engineering approach for confined gas sensors.

Accurate detection of carbon monoxide (CO) concentrations in the exhaled breath of newborns with jaundice is crucial for early diagnosis of the condition. However, the consistency and integration of existing sensors are often constrained by inherent limitations in their manufacturing processes and material systems. Herein, the MEMS micro-hotplate gas sensor based on in-situ grown CuO-In2O3 heterojunction nanocubes. This sensor enables precise, low-power temperature control through a MEMS micro-hotplate. Meanwhile, the in-situ growth technology facilitates a stable interfacial connection between the sensing material and the chip, which contributes to the exceptional consistency in device performance. Concurrently, the in-situ grown 10% CuO-In2O3 heterojunction exhibits a uniform cubic structure, high specific surface area (81.2 m2/g), and large pore size (9.8 nm). This gas sensor exhibits high response toward CO (12.5 at 50 ppm), short response/recovery times (9/48 s), and excellent moisture resistance. More importantly, in batch-produced devices, the consistency error in sensor response is 2.02%, significantly enhancing the reliability and repeatability of device arrays. Density functional theory calculations revealed, at the atomic level, the selective adsorption and charge transfer mechanism of CO molecules at the CuO-In2O3 p-n heterojunction interface, elucidating the intrinsic cause of its enhanced sensitivity. Furthermore, we integrated this sensor with a Bluetooth module, successfully assembling a miniaturised wireless real-time monitoring device. This research establishes the material foundation for developing a new generation of non-invasive, portable bedside monitoring devices for neonatal jaundice.

Fast response and recovery performance is highly significant for real-time monitoring of NH3 gas due to the toxic and harmful feature. However, the commercialization of NH3 gas sensors is still hindered by the limited gas transport channels and sluggish gas-solid kinetics. Herein, a series of highly permeable CeO2 porous hollow microspheres with multilevel gas channels and tunable pore size is developed by modulating the anhydrous citric acid and hydrothermal times of the hydrothermal reaction. The sensor based on CeO2-2 hollow microsphere exhibits fast response speed (15 s) and recovery speed (20 s), high response value (16) to 100 ppm NH3 at 200 degrees C. The unique permeable porous hollow structures as gas transport channels and vast active sites promote the gas-solid kinetics. In addition, a new NH3 reaction process is revealed via in situ diffuse reflectance infrared transform spectroscopy. The gas sensing mechanism is uncovered by density functional theory calculations.

In situ grown 3D CuO nanoarray structures with an ordered architecture have emerged as promising materials for advanced CO gas sensing platforms owing to their intimate anchoring on a substrate, large surface area, and abundant exposed active sites. However, 3D CuO nanoarrays encounter high working temperature, slow response time, and inferior response value, impeding their practical use for CO gas detection. Herein, an Ag electronic sensitization strategy is proposed by a facile in situ deposition method. By innovatively constructing Ag nanoparticle coatings on the surface of CuO nanocone arrays, a high response (R g/R a) of 4.95 to 100 ppm of CO was achieved at a lower temperature of 180 degrees C, which is more than three times higher than that of pure CuO (240 degrees C, R g/R a = 1.53). At the same time, Ag/CuO has a fast response time (t res) of 49 s and a recovery time (t rec) of 56 s, which is at least 19 s shorter than pure CuO. In addition, the sensor has good CO selectivity for other gases such as CO, NH3, C3H6O, and CH4O, as well as long-term stability for 8 weeks (relative error 4.03%), which is better than pure CuO (relative error 6.45%). This excellent performance is mainly attributed to the synergistic effect of the unique nanoarray structure of Ag/CuO and the strong sensitization effect of Ag. Therefore, this study provides a novel and promising strategy for developing high-performance chemical sensors using interfacial engineering.

Noninvasive, precise breath analysis holds significant importance for the screening and monitoring of neonatal jaundice, with its core challenge lying in the specific detection of the key biomarker carbon monoxide (CO) within complex breath matrices. This research employed a controlled process to fabricate five sets of In2O3-CuO sensors derived from bimetallic metal-organic frameworks (Bi MOFs). These were assembled into a microsensor array, and by incorporating a linear discriminant analysis algorithm, an electronic nose system was constructed. This approach utilizes thermodynamic feature engineering to enhance data validity and optimize algorithm selection, thereby reducing reliance on large-scale data and computational resources. By integrating thermodynamically feature-driven machine learning, the electronic nose system-comprising merely five In2O3-CuO sensors-ultimately achieved accurate discrimination between CO and acetone. Concurrently, the single 3In2O3-CuO sensor exhibits excellent reproducibility, moisture resistance, and stability, with a low detection limit of 1 ppm and relatively rapid response/recovery times (5/21 s). By introducing machine learning algorithms to analyze the multidimensional response signals from the sensor array, the study successfully addressed the cross-sensitivity issue between CO and coexisting interfering gas C3H6O in clinical environments, achieving qualitative identification of CO ranging from 1 to 50 ppm (cross-validation accuracy reached 82%), providing a highly reliable technical platform for noninvasive screening of neonatal bilirubin metabolic abnormalities.

Developing a strategy to tailor the morphology and sensing properties of CuO nanosheet arrays for low-temperature, ppb-level selective nitrogen dioxide (NO2) detection is of great significance as it represents a key step toward addressing challenges related to air quality improvement, human health protection, and environmental sustainability. In this work, CuO nanosheets were synthesized via a seed-induced hydrothermal in situ method, which led to a small thickness of 16.72 nm and a high concentration of oxygen vacancies. The as-prepared CuO nanosheets exhibited a high response of 4.65 with short response and recovery times of 59 s and 72 s, respectively, toward 100 ppb NO2 at 75 degrees C. The sensing mechanism was investigated using electron paramagnetic resonance (EPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Density functional theory (DFT) calculations were employed to elucidate the selectivity of NO2 over interfering gases. The in situ grown CuO nanosheets (with thickness comparable to the Debye length) provided expanded reaction interfaces and efficient electron transport channels upon exposure to NO2, which facilitated enhanced interactions between the gas molecules and active sites, improving the sensing response. Moreover, the high concentration oxygen vacancies acted as reactive centers that effectively reduced the reaction energy barrier, enabling ppb-level, highly sensitive, and selective NO2 detection at low operating temperatures. Overall, this work provides a new material for gas sensing, which promises advancements in high-performance, low-temperature NO2 sensors.

Fast response and recovery performance is highly significant for real‐time monitoring of NH 3 gas due to the toxic and harmful feature. However, the commercialization of NH 3 gas sensors is still hindered by the limited gas transport channels and sluggish gas–solid kinetics. Herein, a series of highly permeable CeO 2 porous hollow microspheres with multilevel gas channels and tunable pore size is developed by modulating the anhydrous citric acid and hydrothermal times of the hydrothermal reaction. The sensor based on CeO 2 ‐2 hollow microsphere exhibits fast response speed (15 s) and recovery speed (20 s), high response value (16) to 100 ppm NH 3 at 200 °C. The unique permeable porous hollow structures as gas transport channels and vast active sites promote the gas–solid kinetics. In addition, a new NH 3 reaction process is revealed via in situ diffuse reflectance infrared transform spectroscopy. The gas sensing mechanism is uncovered by density functional theory calculations.

NO is a major factor in blood pressure regulation, but it is also one of the major sources of air pollution. Currently, WO3 is becoming a promising material for developing low temperature gas sensors. However, due to its relatively low sensitivity and high operating temperature, its performance is not satisfactory, which limits its application. Hydrogen substituted graphyne (HsGY), as a new type of two-dimensional material, has excellent conductivity and thermal conductivity, which can effectively dissipate the heat generated by the sensor during operation, thereby reducing the working temperature. Therefore, highly dispersed WO3 nanoparticles anchored on HsGY sheets are synthesized by hydrothermal method. The gas-sensing results show that compared to pure WO3, HsGY@WO3 nanocomposites have a response value of 4.3-20 ppm NO at 150 degrees C. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used to reveal the gas-sensing mechanism. Ultraviolet photoelectron spectroscopy (UPS) is employed to analyze the energy bands, revealing the mechanism behind the improved NO sensitivity. Density functional theory (DFT) calculations are used to explain the selectivity mechanism of NO against other interfering gases. Our research provides novel gas-sensing materials for the development of high performance, low temperature NO gas sensors.

The rational design of gas-sensitive nanomaterials with tailored nanostructures is crucial for the development of next-generation chemosensors. Here, we pyrolyzed Ni/Ce-MOF based on 3,5-pyridinedicarboxylic acid to obtain Ce-NiO with vertically aligned nanowalls while retaining the high specific surface area and pore size distribution of MOF. On the one hand, the layered structure of the nanowalls can greatly shorten the transmission path of the gas-sensitive reaction so that the acetone gas molecules can rapidly contact the active sites on the surface of the material, thus realizing a rapid reaction (8 s/10 s); on the other hand, the rich nanoscale pore structure inside the material provides sufficient space for gas adsorption and diffusion and maintains a highly efficient mass transfer process even in the acetone concentration of up to 175 degrees C environment. During the process, the concentration of 10 ppm acetone shows the maximum response value of 4.2. This study presents an efficient real-time monitoring solution for precise acetone detection, with its technological advancements demonstrating strong potential to facilitate practical applications of portable gas sensing devices in environmental monitoring and industrial safety.

Metal–organic frameworks (MOFs) are newly developed materials for gas sensing applications currently. However, the prolonged response time limits their future applications because of their poor electrical conductivity. In this context, alternating stacked MXene@Cu‐HHTP heterostructures characterized by a sandwich‐type architecture comprised of Cu‐HHTP (copper‐catecholate frameworks), 2D conductive MOFs, and layered MXene achieve high‐performance triethylamine (TEA) sensing. The unique interlayer pore architecture within the MXene@Cu‐HHTP composites facilitates efficient mass transfer of gas molecules while retaining the large surface area and porosity characteristics of the MOFs, leading to rapid TEA response. MXene@Cu‐HHTP composites respond to 50 ppm TEA in only 4 s and low detection limit (1 ppm). Demonstrated higher sensitivity compared to the original Cu‐HHTP sensor (≈21 times at 200 ppm TEA). At room temperature and atmospheric conditions, the value of moisture resistance of MXene@Cu‐HHTP composites can reach 80% through continuous real‐time dynamic testing.

NH3 is a fairly important raw material in a number of fields but harmful to the human. Currently, hydrogen substituted graphyne (HsGY) shows fast response to NH3 gas based on our previous report. However, it still suffers from low response values and humidity interference. CeO2 has the advantage of moisture resistance as NH3 gas sensor but prone to agglomeration, whereas the alkyne bond of HsGY can anchor CeO2 to form a discretely distributed CeO2. Therefore, highly dispersed CeO2 nanocubics anchoring on HsGY sheets are synthesized through hydrothermal method. The gas sensing characteristics show that the gas sensing response value to 80 ppm NH3 is increased by 3 times compared to pure HsGY. Furthermore, they present relatively stable NH3 gas response under relative humidity variation (20-80 %). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used to reveal the gas sensing mechanism. Energy bands are analyzed using ultraviolet photoemission spectroscopy (UPS), revealing the improvement mechanism of NH3 gas-sensitive performance. Density functional theory (DFT) calculations are employed to explain selectivity mechanism to NH3 against other interference gases. Our research provides novel gas sensing materials for the development of high-performance, moisture-resistant room temperature NH3 sensors.

There are a variety of volatile organic compounds (VOCs) gases in human exhalation, and among them isoprene, ethanol, and formaldehyde can be used as biomarkers for liver metabolic diseases. In order to accurately detect these trace-concentration VOC gases, a sensor array was built with 4 MEMS gas sensors, and one of them was the self-developed sensor, which has a very high response to isoprene. To improve prediction accuracy of gas concentration, we investigated the convolutional neural network with a Multi-Expert Temporal Fusion Network (METF-Net) model based on multitask learning. Based on the MEMS sensor array, the isoprene, ethanol, and formaldehyde at sub ppm level can be correctly identified; their RMSEs of isoprene, ethanol, and formaldehyde are 33.48, 64.01, and 18.84 ppb, and the predicted concentrations with error rates of isoprene, ethanol, and formaldehyde are 6.70%, 6.40%, and 9.42%, respectively. This method has the potential of being applied in the screening of liver metabolic diseases at an early stage.

Abstract Large enhancement of nonlinear absorption and nonlinear refraction are achieved simultaneously in highly ordered two dimensional (2D) covalent organic framework (COF) films prepared by solidliquid interface one‐step method to overcome the weakness of COF powders in solubility. In the intrinsic nonlinear optical response obtained at 532 nm with 5 ns pulse, the nonlinear absorption coefficients (β) of two COF films are −4.87 × 10−5 and −1.29 × 10−5 m W−1, respectively. Simultaneously, the fitted closed‐aperture curves also show large nonlinear refractive indexes (n2), −5.62 × 10−12 m2 W−1 and −0.76 × 10−12 m2 W−1. The 4f coherent imaging performed at the same condition with a single‐shot pulse further verifies the outstanding nonlinear optical response without any damage probably experienced in the Z‐scan technique. Moreover, the differences in framework electronic structure and photoexcited states between two COF films are compared to explain the difference in nonlinear optical response. All the results indicate that two COF crystalline films with intrinsic giant nonlinear optical response can be capable of modulating both amplitude and phase of light, providing huge potential in all‐optical manipulating and switching at the nanoscale as outstanding nonlinear optical materials.