A yolk-double-shelled heterostructure-based sensor for acetone detecting application

Advancements in Improving Selectivity of Metal Oxide Semiconductor Gas Sensors Opening New Perspectives for Their Application in Food Industry

Volatile compounds not only contribute to the distinct flavors and aromas found in foods and beverages, but can also serve as indicators for spoilage, contamination, or the presence of potentially harmful substances. As the odor of food raw materials and products carries valuable information about their state, gas sensors play a pivotal role in ensuring food safety and quality at various stages of its production and distribution. Among gas detection devices that are widely used in the food industry, metal oxide semiconductor (MOS) gas sensors are of the greatest importance. Ongoing research and development efforts have led to significant improvements in their performance, rendering them immensely useful tools for monitoring and ensuring food product quality; however, aspects related to their limited selectivity still remain a challenge. This review explores various strategies and technologies that have been employed to enhance the selectivity of MOS gas sensors, encompassing the innovative sensor designs, integration of advanced materials, and improvement of measurement methodology and pattern recognize algorithms. The discussed advances in MOS gas sensors, such as reducing cross-sensitivity to interfering gases, improving detection limits, and providing more accurate assessment of volatile organic compounds (VOCs) could lead to further expansion of their applications in a variety of areas, including food processing and storage, ultimately benefiting both industry and consumers.

A room-temperature formaldehyde sensor based on hematite for breast cancer diagnosis

Formaldehyde (HCHO) is regarded as one kind of indoor pollutant. Additionally, HCHO serves as a biomarker in the exhaled breath of breast cancer patients. Early warning and management are crucial for the environment and human health. Thus, we have elaborately synthesized hematite (α-Fe₂O₃) employing a facet-engineering hydrothermal strategy using the fine-tuned solvent composition, with special attention to the effect of different exposed surfaces on HCHO detection. The spindle-like α-Fe₂O₃ nanocrystals with the (012) facet exposed exhibited impressively higher response towards HCHO at room temperature than that of the disk-like α-Fe₂O₃ with mainly the (001) facet exposed, partly due to the abundant vacancy oxygen and adsorbed oxygen of high-index facets of α-Fe₂O₃. More importantly, our experimental results coincide with theoretical calculations. Overall, the surface engineering strategy could be extended to a versatile approach for HCHO detection.

Zinc Oxide-Based Acetone Gas Sensors for Breath Analysis: A Review

Acetone is one of the toxic, explosive, and harmful gases. It may cause several health hazard issues such as narcosis and headache. Acetone is also regarded as a key biomarker to diagnose several diseases as well as monitor the disorders in human health. Based on clinical findings, acetone concentration in human breath is correlated with many diseases such as asthma, halitosis, lung cancer, and diabetes. Thus, its investigation can become a new approach for health monitoring. Better management at the early stages of such diseases has the potential not only to reduce deaths associated with the disease but also to reduce medical costs. ZnO-based sensors show great potential for acetone gas due to their high chemical stability, simple synthesis process, and low cost. The findings suggested that the acetone sensing performance of such sensors can be significantly improved by manipulating the microstructure (surface area, porosity, etc.), composition, and morphology of ZnO nanomaterials. This article provides a comprehensive review of the state-of-the-art research activities, published during the last five years (2016 to 2020), related to acetone gas sensing using nanostructured ZnO (nanowires, nanoparticles, nanorods, thin films, etc). It focuses on different types of nanostructured ZnO-based acetone gas sensors. Furthermore, several factors such as relative humidity, acetone concentrations, and operating temperature that affects the acetone gas sensing properties- sensitivity, long-term stability, selectivity as well as response and recovery time are discussed in this review. We hope that this work will inspire the development of high-performance acetone gas sensors using nanostructured materials.

High acetone sensing properties of In2O3-NiO one-dimensional heterogeneous nanofibers based on electrospinning

Pure NiO nanofibers and the In2O3-NiO one-dimensional heterogeneous nanofibers were prepared by electrospinning, and the gas sensing properties to acetone were also investigated. Material characterization proved that the heterogeneous nanofibers were composed of In2O3 and NiO, and the nanofibers exhibited an enhanced sensitivity to acetone. At the optimal working temperature, the response of In2O3-NiO nanofibers to 50 ppm acetone was more than 10 times higher than that of pure NiO nanofibers. The minimum detection limit of the heterogeneous nanofibers reached 10 ppb, while the pure NiO nanofibers only reached 100 ppb. Among acetone and the comparison gases (methanol, ethanol, triethylamine, ethyl acetate, and benzene), the heterogeneous nanofibers achieved the highest response to acetone. In addition, the heterogeneous nanofibers exhibited an improved response-recovery rate and good long-term stability. These results indicated that the In2O3-NiO one-dimensional heterogeneous nanofibers have great potential in low-concentration acetone detection. Combined with the material properties, the mechanism of the enhanced sensing properties was discussed in detail for the In2O3-NiO heterogeneous nanofibers.

Synthesis and acetone sensing properties of ZnFe2O4/rGO gas sensors

Hollow spheres of pure ZnFe₂O₄ and of composites of ZnFe₂O₄ and reduced graphene oxide (rGO) with different rGO content were prepared via a simple solvothermal method followed by a high-temperature annealing process in an inert atmosphere. The X-ray diffraction analysis confirmed that the introduction of rGO had no effect on the spinel structure of ZnFe₂O₄. In addition, the results of field-emission scanning electron microscopy and (high-resolution) transmission electron microscopy indicated that the synthesized samples had the structure of hollow spheres distributed uniformly onto rGO nanosheets. The diameters of the spheres were determined as about 600-1000 nm. The gas sensing test revealed that the introduction of rGO improved the performance of the sensing of acetone to low concentration, and the ZnFe₂O₄/rGO composite gas sensor containing 0.5 wt % of rGO exhibited a high sensitivity in sensing test using 0.8-100 ppm acetone at 200 °C. The response of the 0.5 wt % ZnFe₂O₄/rGO sensor to 0.8 ppm acetone was 1.50, and its response to 10 ppm acetone was 8.18, which is around 2.6 times more pronounced than the response of pure ZnFe₂O₄ (10 ppm, 3.20). Moreover, the sensor showed a wide linear range and good selectivity.

Enhanced acetone sensor based on Au functionalized In-doped ZnSnO3 nanofibers synthesized by electrospinning method

Nobel metal modification could be a valuable method for the fabrication of advanced chemiresistive gas sensor. Herein, a series of Au loaded In-doped ZnSnO₃ nanofibers were prepared via electrospinning technique. The crystal structure, morphology and chemical composition of the synthesized materials were characterized by field-emission X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental mapping, X-ray photoelectron spectroscopy (XPS) and Brunauere-Emmette-Teller (BET) analyses. The optimal sensor, which was based on 0.25 mol% Au loaded In-doped ZnSnO₃ nanofibers, could detect 50 ppm acetone effectively, it possessed a high response (19.3) and fast response/recovery time (10/13 s) at low operating temperature (200 °C). The enhanced gas sensing performance was mainly derived from proper introduction of Au. Since the electronic catalysis of Au nanoparticles created Schottky barrier-type junctions at Au and ZnSnO₃ interfaces which could cause tremendous change of resistance and induce to high sensitivity, meanwhile the chemical catalysis of Au nanoparticles promoted the chemisorption and dissociation of gas molecules which could accelerate the reaction with gas sensing material. Moreover, the Au loaded In-doped ZnSnO₃ sensors displayed certain stability under different humidity condition, it meant that the negative influence of water vapor on gas sensing performance could be inhibited by loading Au nanoparticles.