Abstract
An electronic nose (Enose) relies on the use of an array of partially selective chemical gas sensors for identification of various chemical compounds, including volatile organic compounds in gas mixtures. They have been proposed as a portable low-cost technology to analyse complex odours in the food industry and for environmental monitoring. Recent advances in nanofabrication, sensor and microcircuitry design, neural networks, and system integration have considerably improved the efficacy of Enose devices. Here, we highlight different types of semiconducting metal oxides as well as their sensing mechanism and integration into Enose systems, including different pattern recognition techniques employed for data analysis. We offer a critical perspective of state-of-the-art commercial and custom-made Enoses, identifying current challenges for the broader uptake and use of Enose systems in a variety of applications.
Highlights
Irrespective of the type of Semiconducting metal oxides (SMO) used as the active layer, the gas sensing mechanisms in an SMO based chemiresistive gas sensor are primarily due to the catalytic interactions on the sensing layer as well as the diffusivity of target gas molecules into the system
In order to differentiate between commonly produced volatile organic compounds (VOCs) from food preservatives such as ethanol, acetone, nitrogen dioxide, and ozone, Zappa fabricated a custom-made electronic nose (Enose) consisting of three distinct metal oxide (WO3, SnO2, CuO) nanowires that were directly synthesised on micro-hotplates [84]
The combination of gas sensor arrays along with data acquisition systems provides Enoses with a potential for numerous applications in the food industry to differentiate between adulterants and establish quality
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. This idea was further developed 20 years later by Persaud and Dodd in 1982, who developed the first Enose system using semiconducting transducers that could discriminate various odours with high sensitivity and specificity [7] Their proposed Enose worked on a similar principle as the mammalian olfactory system. Gas mixtures have been analysed using techniques such as gas chromatography (GC) [13], ion mobility spectrometry (IMS) [14], and proton-transfer-reaction mass spectrometry (PTR-MS) [15] These approaches provide qualitative and quantitative analysis of vapours but require expert personnel and have high operational cost and time consuming sample preparation and analysis [16].
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