Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas. However, it can have dangerous effects on human life and health. Thus, the ...realization of sensitive and selective sensors for recognition of acetone is highly important. Among different gas sensors, resistive gas sensors based on nanostructured metal oxide with high surface area, have been widely reported for successful detection of acetone gas, owing to their high sensitivity, fast dynamics, high stability, and low price. Herein, we discuss different aspects of metal oxide-based acetone gas sensors in pristine, composite, doped, and noble metal functionalized forms. Gas sensing mechanisms are also discussed. This review is an informative document for those who are working in the field of gas sensors.
Display omitted
•Creation of a novel self-heated CO gas sensor based on Au-functionalized networked SnO2-ZnO core-shell nanowires.•Increasing the applied voltage particularly enhanced the ...self-heating effect.•Power consumption at 3 and 20 V was estimated to be 11.3 nW and 8.3 μW.
We report a novel self-heated CO gas sensor based on Au-functionalized networked SnO2-ZnO core-shell nanowires. Increasing the applied voltage particularly enhanced the sensing response due to the self-heating effect within the sensor, and the sensors exhibited good performance without the need for an external heater. The power consumption at 3 and 20 V was estimated to be 11.3 nW and 8.3 μW, respectively. In a sensor with the optimal ZnO shell thickness of 80 nm, the responses for 50 ppm CO were 1.17 and 1.62 at 3 and 20 V, respectively. Also, the important role of ZnO-ZnO homojunctions in the self-heating of the sensor was demonstrated by increasing the ZnO shell thickness, which led to an increase in the sensor response. Furthermore, the optimized sensor exhibited outstanding selectivity toward CO gas. The optimized ZnO shell, the catalytic effect of Au, and the Joule effect contributed to the good, selective response toward CO gas with low power consumption. Since low power consumption is a fundamental requirement for wireless sensors and sensor arrays, this sensor with very low power consumption is a promising choice for such applications.
•Preparation of superhydrophobic austenitic stainless steel surfaces using an etching method.•Study of effects of HF etchant and NaCl solution on the final surface properties.•The highest water ...contact angle was 168° with a sliding angle of 2°.•Excellent durability after 30 days was demonstrated.•The fabricated surfaces showed self-cleaning properties.
Stainless steels are among the most common engineering materials and are used extensively in humid areas. Therefore, it is important that these materials must be robust to humidity and corrosion. This paper reports the fabrication of superhydrophobic surfaces from austenitic stainless steel (type AISI 304) using a facile two-step chemical etching method. In the first step, the stainless steel plates were etched in a HF solution, followed by a fluorination process, where they showed a water contact angle (WCA) of 166° and a sliding angle of 5° under the optimal conditions. To further enhance the superhydrophobicity, in the second step, they were dipped in a 0.1 wt.% NaCl solution at 100 °C, where the WCA was increased to 168° and the sliding angle was decreased to ∼2°. The long-term durability of the fabricated superhydrophobic samples for 1 month storage in air and water was investigated. The potential applicability of the fabricated samples was demonstrated by the excellent superhydrophobicity after 1 month. In addition, the self-cleaning properties of the fabricated superhydrophobic surface were also demonstrated. This paper outlines a facile, low-cost and scalable chemical etching method that can be adopted easily for large-scale purposes.
•Applications of core-shell nanostructures in gas sensors are discussed.•Mechanisms of gas sensing in core-shell nanostructures are discussed.•Effect of shell thickness is comprehensively discussed.
...High-performance gas sensors are needed to improve safety in daily life. Even though the gas sensing performance of new nanostructured metal oxides has improved significantly, some aspects of these novel nanomaterials have not been fully explored. Core-shell (C-S) and hollow shell nanostructures are two types of advanced materials for gas sensing applications. Their popularity is mainly due to the synergetic effects of the core and shell in C-S nanostructures, the high surface areas of both C-S and hollow nanostructures, and the possibility of tuning the shell thickness within the range of the Debye length for such nanostructures. In addition to the type of sensing material, morphology, sensing temperature, and porosity, shell thickness is one of the most important design parameters. Unfortunately, less attention has been paid to the effect of shell thickness on the gas sensing properties. Herein, we demonstrate that the thickness has an undeniable role in the gas sensing response of the resulting material. In this review, we present the first overview of this aspect of sensing materials. By referring to related works, we show how shell thickness can affect the sensing properties of both C-S and hollow nanostructures. Researchers in this field will be able to fabricate more sensitive gas sensors for real applications by better understanding the effect of shell thickness on the gas sensing properties of C-S and hollow nanostructured materials.
There is no consensus regarding the clinical significance of CD44 and CD24 as cancer stem cell (CSC) marker in colorectal cancer (CRC).
A total of 494 CRC samples (2008-2017) were assessed for CD44 ...(epithelial isoform) and CD24 expression using tissue microarray.
CD24 individually or in combination with CD44 was not associated with any of the clinicopathologic characteristics of the tumor. CD44 expression was inversely associated with pathological Tumor, Node, Metastasis (pTNM) lower stages (p = 0.038) and lymphatic invasion (p = 0.05).
In summary, the epithelial isoform of CD44 is inversely associated with invasive characteristics of CRC.
Display omitted
•Bare, Au-, SnO2-, and Au-SnO2-decorated WS2 nanosheets were prepared for CO sensing.•Gas sensing studies were performed under self-heating mode with a low power ...consumption.•Au-SnO2-co-decorated WS2 nanosheet showed the highest response of 3.687 to 50 ppm CO gas at 4.7 V.•Optimized gas sensor revealed high flexibility under tilting, bending, and stretching conditions.•Underlying sensing mechanism is explained in detail.
In this study, WS2 nanosheets that are bare or decorated with Au, SnO2, or a combination of Au and SnO2 were realized on flexible polyamide substrates. The fabricated sensors were operated for CO gas sensing in applied-voltage-induced self-heating mode. Not only optimal applied voltage was varied for the sensing of different gases, but also that the sensors behaved uniquely in response to CO gas. In particular, the Au-SnO2-co-decorated WS2 nanosheet gas sensor under an optimized applied voltage of 4.7, displayed the highest response (Ra/Rg = 3.687–50 ppm CO gas) and the highest selectivity to CO gas among the different gas sensors investigated. Furthermore, the optimized gas sensor indicated good gas response under tilting, bending and stretching conditions. The formation of Au-WS2 Schottky junctions, SnO2-WS2 heterojunctions and the role played by Au NPs in the catalysis CO gas were the most contributed effects to the sensing. The results obtained in this study provide new avenues towards fabrication of flexible, low power gas sensors using metal chalcogenides.
Reduced graphene oxide (rGO) is a reduced form of graphene oxide used extensively in gas sensing applications. On the other hand, in its pristine form, graphene has shortages and is generally ...utilized in combination with other metal oxides to improve gas sensing capabilities. There are different ways of adding rGO to different metal oxides with various morphologies. This study focuses on rGO-loaded metal oxide nanofiber (NF) synthesized using an electrospinning method. Different amounts of rGO were added to the metal oxide precursors, and after electrospinning, the gas response is enhanced through different sensing mechanisms. This review paper discusses rGO-loaded metal oxide NFs gas sensors.
In this study, sputtered-assisted CuO-decorated ZnO nanorod (NR) gas sensors were fabricated for ethanol gas sensing studies. CuO nanoparticles have been successfully formed on ZnO nanorods by means ...of a physical process as the decorative metallic element. The amount of decoration affecting the sensor's performance has been optimized. Cu layers with different thicknesses of 5, 10, and 20 nm were deposited on hydrothermally grown ZnO NRs using the sputtering technique. Upon subsequent annealing, Cu was oxidized to CuO. The gas sensing studies revealed that the sensor with an initial Cu layer of 5 nm had the highest response to ethanol at 350 °C. The sensor also showed good selectivity, repeatability, and long-term stability. The enhanced ethanol sensing response of the optimized gas sensor is related to the formation of p-n heterojunction between p-type CuO and n-type ZnO and the presence of the optimal amount of CuO on the surface of ZnO NRs. The results presented in this study highlight the need for optimizing the amount of Cu deposition on the surface of ZnO NRs in order to achieve the highest response to ethanol gas.
In this paper, we have developed an in-vehicle wireless driver breath alcohol detection (IDBAD) system based on Sn-doped CuO nanostructures. When the proposed system detects the ethanol trace in the ...driver`s exhaled breath, it can alarm and then prevents the car to be started and also sends the location of the car to the mobile phone. The sensor used in this system is a two-sided micro-heater integrated resistive ethanol gas sensor fabricated based on Sn-doped CuO nanostructures. Pristine and Sn-doped CuO nanostructures were synthesized as the sensing materials. The micro-heater is calibrated to provide the desired temperature by applying voltage. The results showed that by Sn-doping in CuO nanostructures, the sensor performance can be significantly improved. The proposed gas sensor has a fast response, good repeatability along with good selectivity that makes it suitable for being used in practical applications such as the proposed system.
PDF
