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Approximately one in 10 people worldwide suffer from irritable bowel syndrome (IBS). Thus, early diagnosis and simple monitoring of chronic diseases will help to improve the patient's quality of life. Herein, we report a chemiresistive-type gas sensor for exhaled hydrogen detection that was fabricated by combining hierarchically porous SnO2 nano-architectures and PdO. The unique structured PdO-functionalized SnO2 hydrogen sensor exhibited excellent selectivity (response ratio > 5.2), high response (resistance ratio = 6.3), extremely fast sensing kinetics (response speed: 4.0 s and recovery period: 36.2 s), and low detection limit (0.096 ppm) under high humidity (relative humidity 80%). These exceptional sensing properties toward hydrogen were investigated from multiple perspectives, including effective gas diffusion through multimodal pores, changes in charge-carrier concentration in p–n heterojunctions, and the catalytic effect of PdO. The proposed sensor has a high potential for practical high-performance hydrogen sensor applications and will offer new possibilities for a simple disease diagnosis based on breath analysis. [ABSTRACT FROM AUTHOR]

The precise detection of trace concentrations of ethylene, a plant hormone gas, is essential for controlling plant health and status. However, owing to the simple chemical structure and low reactivity of ethylene, the highly sensitive and exclusive detection of ethylene has been a significant challenge, despite the strong demand from the agricultural industry. Herein, we report a novel bilayer ethylene gas sensor consisting of a Pd-doped V2O5–TiO2 yolk–shell catalytic overlayer and an In2O3 sensing layer. The coating of 2 wt% Pd-doped V2O5–TiO2 on the In2O3 sensing film remarkably enhances the ethylene response and selectivity over a wide range of operating temperatures (300–400 °C). This is attributed to the reforming of ethylene into more reactive acetaldehyde and the filtering of interference gas into non-reactive forms using the unique Pd–V2O5–TiO2 catalytic overlayer for heterogeneous Wacker oxidation promoted by the yolk–shell sphere structure. To the best of our knowledge, this paper presents the first report on the design of a catalytic overlayer that converts less-reactive ethylene into more-reactive species. The outstanding capability of the unique bilayer sensor proposed in this study enables the monitoring of the ripeness of fruits and correlates well with the results of proton transfer reaction-quadrupole mass spectrometry (PTR-QMS). [ABSTRACT FROM AUTHOR]

Bimetallic Fe/Ni-based metal-organic frameworks (MOFs) with different Fe/Ni ratios were coated on TiO2 nanorods (NRs), and the performances of the heterojunction photoanodes in photoelectrochemical water splitting were investigated. The bandgaps and band positions of the MOFs could be modulated by changing the ratio of the Fe and Ni components. An ideal band alignment was achieved between the TiO2 NRs and bimetallic MOFs with an optimum ratio of [Fe]/[Ni] = 0.25/0.75, which allowed efficient light absorption and charge separation. The coating of NH2−MIL(Fe)−88 layer on the TiO2 NRs decreased the photocurrent density by 33%. In comparison, TiO2/NH2−MIL(Ni)−88 showed a modest improvement in photocurrent density (0.85 mA·cm−2 at 1.23 V vs. a reversible hydrogen electrode (RHE)). When bimetallic NH2−MIL(Fe0.25Ni0.75)−88 was coated on the TiO2 NRs, the photocurrent density reached 1.56 mA·cm−2, which was an efficiency enhancement of 3.2 times. The mechanism underlying high photoelectrochemical performance was investigated. [ABSTRACT FROM AUTHOR]

Porous CuBr films are the most promising platform for the exclusive detection of NH3 but their simple and cost-effective fabrication without employing a high-temperature process remains elusive. Herein, we report the facile and low-temperature preparation of porous CuBr films by a solution oxidation method, and their unprecedentedly high NH3 sensing properties. The porous CuBr films are prepared by coating Cu thin films with different thicknesses (10–100 nm) on sensor substrates by direct current sputtering, immersion of Cu thin films in a CuBr2 solution (0.001–0.1 M) for a controlled time (10–300 s), and washing of the substrate with methanol. Among the CuBr film sensors, the sensor fabricated by immersing the 30 nm-thick Cu film in 0.01 M CuBr2 solution for 120 s (30n-120s sensor) exhibits the highest NH3 response (resistance ratio = 211), which is the highest level compared with those reported in the literature. Moreover, the 30n-120s sensor exhibits ultrahigh NH3 selectivity, extremely low detection limit (∼25 ppb), excellent reversibility, and long-term stability at room temperature. The sensing film of the 30n-120s sensor has a porous structure consisting of loosely percolated CuBr particles, whereas the other films have a dense structure with tightly percolated particles or, conversely, an island configuration composed of nearly discrete particles. The superior NH3 sensing properties of the sensor are discussed in terms of the porosity and particle connectivity of the film. The high performance NH3 sensor can be used to realize flexible and even wearable NH3 detectors for emerging applications such as environmental monitoring, food freshness assessment, and breath analysis for disease diagnosis. [ABSTRACT FROM AUTHOR]

Precise detection of breath isoprene can provide valuable information for monitoring the physical and physiological status of human beings or for the early diagnosis of cardiovascular diseases. However, the extremely low concentration and low chemical reactivity of breath isoprene hamper the selective and sensitive detection of isoprene using oxide semiconductor chemiresistors. Herein, we report that macroporous WO 3 microspheres whose inner macropores are surrounded by Au nanoparticles exhibit a high response (resistance ratio = 11.3) to 0.1 ppm isoprene under highly humid conditions at 275 °C and an extremely low detection limit (0.2 ppb). Furthermore, the sensor showed excellent selectivity to isoprene over five interferants that could be exhaled by humans. Notably, the selectivity to isoprene is critically dependent on the location of Au nanocatalysts and macroporosity. The mechanism underlying the selective isoprene detection is investigated in relation to the reforming of less reactive isoprene into more reactive intermediate species promoted by macroporous catalytic reactors, which is confirmed by the analysis using a proton transfer reaction quadrupole mass spectrometer. The sensor for breath analysis has high potential for simple physical and physiological monitoring as well as disease diagnosis.