Considering that the volatile content of isoamyl alcohol will increase sharply on the seventh day during wheat mildew, isoamyl alcohol can be determined as an early biomarker of wheat mildew. Currently, there are only few sensors reported for isoamyl alcohol detection, which still suffer from low sensitivity and poor moisture resistance. Herein, the sensitivity of 5 at% Er@LaFeO₃ (ELFO) for isoamyl alcohol was enhanced by loading Ag nanoparticles on the surface of the ELFO microspheres while the optimal operating temperature was reduced. The moisture resistance of Ag/ELFO was improved by the incorporation of g-C₃N₄ nanosheets (NSs) on the surface of Ag/ELFO through electrostatic self-assembly. Given the requirement of practical application in grain granaries, the sensing behavior of g-C₃N₄ NSs incorporated Ag/ELFO-based sensor at 20% RH was systematically studied, which demonstrated excellent repeatability, long-term stability, and superior selectivity (791 at 50 ppm) for isoamyl alcohol with a low limit of detection (LOD = 75 ppb). Furthermore, the practical results of wheat at different mildew stages further confirmed the application potential of the g-C₃N₄/Ag/ELFO-based sensor in monitoring the early mildew stage of wheat. This work may offer guidance for enhancing the moisture resistance of gas-sensitive materials through the strategy of employing composite nanomaterials.

In the early-stage diagnosis of lung cancer, the low-concentration (< 5 ppm) volatile organic compounds (VOCs) are extensively identified to be the biomarkers for breath analysis. Herein, the urchin-like sodium (Na)-doped ZnO nanoneedles were synthesized through a hydrothermal strategy with the addition of different contents of citric acid. The Na-doped ZnO gas sensor with a 3:1 molar ratio of Na⁺ and citric acid showed outstanding sensing properties with an optimal selectivity to various VOCs (formaldehyde, isopropanol, acetone and ammonia) based on working temperature regulation. Specifically, significantly enhanced sensitivity (21.3 @ 5 ppm) compared with pristine ZnO (~ seven-fold), low detection of limit (LOD) (298 ppb), robust humidity resistance and long-term stability of formaldehyde sensing performances were obtained, which can be attributed to the formation of a higher concentration of oxygen vacancies (20.98%) and the active electron transitions. Furthermore, the improved sensing mechanism was demonstrated by the exquisite band structure and introduction of the additional acceptor level which resulted in the narrowed bandgap of ZnO.

In the assessment of food quality, geranyl acetone plays a crucial role as a volatile organic compound (VOC) biomarker for diverse agricultural products, while the ultralow concentration detection meeting application requirements has been barely studied. Herein, an iron (Fe)-doped WO_3−x gas sensor was employed for greatly sensitive, selective, and scalable geranyl acetone detection. The results proved that precisely-regulated oxygen vacancy (O_V) and sophisticatedly-active electron transition of Fe-doped WO_3−x nanoparticles were fulfilled by modifying the doping amount of Fe³⁺, leading to the prominently enhanced sensitivity (23.47 at 6 ppm), low limit of detection (LOD) (237 ppb), optimal selectivity, and outstanding long-term stability. Furthermore, the enhancing mechanism of gas sensing performance was substantiated through density functional theory (DFT) calculation, while the practical application for the evaluation of spoiled cooked rice was conducted as well. This study demonstrates a reliable method for detecting a VOC biomarker in cooked rice, which can ensure food security and improve palatability of cooked rice.

2D MXenes are highly attractive for fabricating high-precision gas sensors operated at room temperature (RT) due to their high surface-to-volume ratio. However, the limited selectivity and low sensitivity are still long-standing challenges for their further applications. Herein, the self-assembly of 0D–2D heterostructure for highly sensitive NO₂ detection was achieved by integrating ZnO nanoparticles on Ti₃C₂T_x MXene-derived TiO₂ nanosheets (designated as ZnO@M−TiO₂). ZnO nanoparticles can not only act as spacers to prevent the restacking of M−TiO₂ nanosheets and ensure effective transfer for gas molecules, but also enhance the sensitivity of the sensor the through trapping effect on electrons. Meanwhile, M−TiO₂ nanosheets facilitate gas diffusion for rapid sensor response. Benefiting from the synergistic effect of individual components, the ZnO@M−TiO₂ 0D–2D heterostructure-based sensors revealed remarkable sensitivity and excellent selectivity to low concentration NO₂ at RT. This work may facilitate the sensing application of MXene derivative and provide a new avenue for the development of high-performance gas sensors in safety assurance and environmental monitoring.

The urgency of early lung cancer (LC) diagnosis and treatment has been more and more significant. Exhaled breath analysis using gas sensors is a promising way to find out if someone has LC due to its low-cost, non-invasive, and real-time monitoring compared with traditional invasive diagnostic techniques. Among sensor-based gas detection techniques, metal oxide semiconductor’s gas sensors are one of the most important types. This review presents the-state-of-art in metal oxide gas sensors for the diagnosis of early LC. First, the exhaled breath biomarkers are described with emphasis on the concentration of abnormal volatile organic compounds (VOCs) caused by the metabolic process of LC cells. Then, the research status of metal oxide gas sensors in LC diagnosis is summarized. The sensing performance and enhancement strategy of biomarkers provided by metal oxide semiconductor materials are reviewed. Another effective way to improve VOC detection performance is to build a gas sensor array. At the same time, various gas sensors combined with self-powered techniques are mentioned to display a broad development prospect in breath diagnosis. Finally, metal oxide gas sensor-based LC diagnosis is prospected.

It is a huge challenge for metal oxide semiconductor gas sensors to inspect volatile organic compounds (VOCs) at room temperature (RT). Herein, the effective utilization of cerium oxide (CeO₂) nanowires for RT detection of VOCs was realized via regulating its surface chemical state. Oxygen vacancy engineering on CeO₂ nanowires, synthesized via hydrothermal method, can be manipulated by annealing under various controlled atmospheres. The sample annealed under 5%H₂+95%Ar condition exhibited outstanding RT sensing properties, displaying a high response of 16.7 towards 20 ppm linalool, a fast response and recovery time (16 and 121 s, respectively), and a low detection of limit of 0.54 ppm. The enhanced sensing performance could be ascribed for the synergistic effects of its nanowire morphology, the large specific surface area (83.95 m²/g), and the formation of extensive oxygen vacancy accompanied by an increase in Ce³⁺. Additionally, the practicability of the sensor was verified via two varieties of rice (Indica and Japonica rice) stored in various periods (1, 3, 5, 7, 15, and 30 d). The experimental results revealed that the sensor was able to distinguish Indica rice from Japonica rice. Accordingly, the as-developed sensor delivers a strategic material to develop high-performance RT electronic nose equipment for monitoring rice quality.

In order to detect low concentrations of volatile organic compounds (VOCs) for the early diagnosis of lung cancer, sensors based on hollow spheres of In₂O₃ were prepared through the soft template method. Ag nanoparticle decorated In₂O₃ composites were synthesized via dipping and annealing. The microstructure, phase composition, element distribution, and state of Ag were analyzed by the scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The gas sensing tests showed that Ag-In₂O₃ sensors had the highest response to isopropanol at 300 ℃. The best response of Ag-In₂O₃ composite sensor was 5.2, which had a significant improvement compared with only In₂O₃. Moreover, the response and recovery time of Ag-In₂O₃ composite sensor was significantly shortened. The improved sensing properties of Ag-In₂O₃ composite sensor could be attributed to the Schottky barrier created at Ag-In₂O₃ interface and catalytical effect of Ag.

Inspired by the micro-nano structure on the surface of biological materials or living organisms, micro-nano structure has been widely investigated in the field of functional coatings. Due to its large specific surface area, porosity, and dual-scale structure, it has recently attracted special attention. The typical fabrication processes of micro-nano structured coatings include sol-gel, hydrothermal synthesis, chemical vapor deposition, etc. This paper presents the main features of a recent deposition and synthesis technique, liquid plasma spraying (LPS). LPS is an important technical improvement of atmospheric plasma spraying. Compared with atmospheric plasma spraying, LPS is more suitable for preparing functional coatings with micro-nano structure. Micro-nano structured coatings are mainly classified into hierarchical-structure and binary-structure. The present study reviews the preparation technology, structural characteristics, functional properties, and potential applications of LPS coatings with a micro-nano structure. The micro-nano structured coatings obtained through tailoring the structure will present excellent performances.