Electronic noses based on metal oxide nanowires: A review

Abstract

Metal oxides are ideal for the fabrication of gas sensors: they are sensitive to many gases while allowing the device to be simple, tiny, and inexpensive. Nonetheless, their lack of selectivity remains a limitation. In order to achieve good selectivity in applications with many possible interfering gases, the sensors are inserted into an electronic nose that combines the signals from nonselective sensors and analyzes them with multivariate statistical algorithms in order to obtain selectivity. This review analyzes the scientific articles published in the last decade regarding electronic noses based on metal oxide nanowires. After a general introduction, Section 2 discusses the issues related to poor intrinsic selectivity. Section 3 briefly reviews the main algorithms that have hitherto been used and the results they can provide. Section 4 classifies the recent literature into fundamental research, agrifood, health, security. In Section 5, the literature is analyzed regarding the metal oxides, the surface decoration nanoparticles, the features that differentiate the sensors in a given array, the application for which the device was developed, the algorithm used, and the type of information obtained. Section 6 concludes by discussing the present state and points out the requirements for their use in real-world applications.

Enhancing peel strength between liquid crystal polymer and copper with plasma treatment, surface oxidation, and silane coating

“…The chemical species of the copper surface after oxidation were studied using the XPS observation (Figure 4f). The intensities of cuprous oxide (Cu 2 O) peaks at 932.2 eV are much higher than copper oxide (CuO) peaks at 934.3 eV as seen from Cu 2p3/2 spectra 33 . Based on XPS results, it is implied that cuprous oxide (Cu 2 O) mainly appears on the surface of copper in the oxidation process, 34 which is consistent with the XRD patterns above.…”

“…The intensities of cuprous oxide (Cu 2 O) peaks at 932.2 eV are much higher than copper oxide (CuO) peaks at 934.3 eV as seen from Cu 2p3/2 spectra. 33 Based on XPS results, it is implied that cuprous oxide (Cu 2 O) mainly appears on the surface of copper in the oxidation process, 34 which is consistent with the XRD patterns above. As a result of the oxidation process, cuprous oxide became the available sites for silane coupling agent to graft functional groups on the oxidized copper surface.…”

Review on Porosity Control in Nanostructured Semiconducting Metal Oxides and Its Influence on Chemiresistive Gas Sensing

“…Among them, SMOs have been widely used as gas-sensing layers due to their superior gas sensitivity at elevated temperatures. − In particular, nanostructured materials have been actively investigated in the gas sensor . Thus far, different synthetic methods for porous nanostructured SMOs have been reported including electrospinning, ,− spray pyrolysis, hydrothermal, solvothermal, , and direct precipitation. , On the other hand, various techniques to overcome their poor intrinsic gas selectivity have been suggested including functionalization with catalysts, − defect creation, phase control, and coating with selectivity overlayer. ,, Many publications ,− summarizing the performance of state-of-the-art SMOs concerning sensitivity, selectivity, sensing mechanisms, and morphology engineering have been widely reported.…”

Nanosensor Based on Thermal Gradient and Machine Learning for the Detection of Methanol Adulteration in Alcoholic Beverages and Methanol Poisoning

“…Although SnO 2 is one of the metal oxides with the best properties and therefore most used for gas sensors, even the finest nanostructures such as cross-linked porous nanosheets [ 20 ] and hollow nanoparticles [ 21 ] exhibit very similar responses to these two gases, making them difficult to distinguish. Therefore, chemoresistors are usually joined in arrays called electronic noses, which exploit different materials to obtain good selectivity [ 22 , 23 ]. The interest in electronic noses leads to the study of the most innovative materials, such as graphene and graphene oxide, and the use of algorithms such as the support vector machine (SVM) allows one to obtain good quantitative results [ 24 ].…”