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The development of one-step deposition technology for metal oxide-based coatings is significant for the rapid fabrication of gas sensors. Gas sensors based on LaFeO3 were fabricated by solution precursor plasma spraying (SPPS) strategy. Through a comparative analysis of material composition and cross-sectional morphology, we have determined the optimal spray distance (8 cm), ensuring the highest level of thickness uniformity in the coating (17.13 ± 0.34 μm). Furthermore, the influence of the number of passes on coating morphology and gas sensing performance was investigated. The optimal gas sensor possessed a higher response to isoamyl alcohol (236 at 25 ppm) at 250 °C. Meanwhile, excellent selectivity, repeatability, long-term stability (431.6 ± 9.2 at 60 ppm for 20 days), and a low limit of detection (144 ppb) were obtained. The superior low-concentration (< 25 ppm) gas-sensing performance should be ascribed to the loose porous morphology with uniform thickness and the higher surface activity of the optimal coating. Moreover, the practical experiment demonstrated the application potential of the sensors for monitoring wheat mildew. This work may provide a direction for the characteristic gas detection of wheat mildew and a successful case for the deposition of LaFeO3 coating by SPPS. [ABSTRACT FROM AUTHOR]

It is essential for food safety to recognize isoamyl alcohol, one of the biomarkers of wheat mildew. However, there has been limited research on isoamyl alcohol gas sensors with superior sensing performance. Herein, highly sensitive Er-doped LaFeO3-based sensors were fabricated using simple hydrothermal combined with dip-coating, and 5 at% Er@LaFeO3 exhibited extraordinary response (219.1 @ 25 ppm), outstanding selectivity, repeatability (435.7 ± 5.0 @ 50 ppm), and long-term stability (432.0 ± 8.2 @ 15 days). The superior isoamyl alcohol sensing performance could be ascribed to several factors, including the smaller particle size (3.02 μm), higher concentration of oxygen vacancies (21.3%) and chemisorbed oxygen (36.2%), larger specific surface area (54.102 m2 g−1), and narrower band gap (1.86 eV). DFT calculations elucidated the sensitization mechanism of Er doped LaFeO3: the reduction in adsorption energy and the enhancement of interaction forces between gas molecules and the sensing coating. Furthermore, the practical application of 5 at% Er@LaFeO3 to volatile gases generated from stored wheat confirmed the potential of fabricated Er-doped LaFeO3 microsphere-based sensors in the analysis of wheat mildew. This work may serve as a guide for the selection of sensing materials to detect biomarkers emitted throughout the wheat mildew process, which may contribute to developing non-destructive and rapid detection technology to minimize losses during wheat storage. [ABSTRACT FROM AUTHOR]

Owing to the advantages of the high specific surface area, excellent electronic conduction behavior, and special diffusion pathways originating from nanoscale heterojunctions, there is a need to analyze the representative gaseous biomarkers that contribute to the wide application of nanostructured metal oxide heterojunction-based gas sensors. Herein, we describe different available routes, including electrospinning, chemical/physical vapor deposition, atomic layer deposition, and hydrothermal routes, for optimizing the crystallinity and morphology of heterojunctions, and the effects of the major parameters of these methods on the gas-sensing performance are deeply explored. On the basis of analyzing the correlations among the process–structure properties, the effects of heterojunctions on the elevated gas-sensing properties are mainly manifested in reducing the operating temperature and improving the sensitivity, selectivity, and humidity resistance. The limitations that exist inside the heterojunctions are also highlighted. This review also proposes insights into the limitations and future topics on the utilization of nanostructured metal oxide heterojunctions. Ultimately, it is expected that this study will provide a fundamental theory for breaking through the limitations of the heterojunctions and further promote their application in environmental monitoring, disease diagnosis, and food quality assessment. [ABSTRACT FROM AUTHOR]