Abstract

Since the first attempts to mimic the human nose with artificial devices, a variety of sensors have been developed, ranging from simple inorganic and organic gas detectors to biosensing elements incorporating proteins of the biological olfactory system. In order to design a device able to mimic the human nose, two major issues still need to be addressed regarding the complexity of olfactory coding and the extreme sensitivity of the biological system. So far, only 50 of the approximately 300–400 functioning olfactory receptors have been de-orphanized, still a long way from breaking the human olfactory code. On the other hand, the exceptional sensitivity of the human nose is based on amplification mechanisms difficult to reproduce with electronic circuits, and perhaps novel approaches are required to address this issue. Here, we review the recent literature on chemical sensing both in biological systems and artificial devices, and try to establish the state-of-the-art towards the design of an electronic nose.

Highlights

  • Parallel to our progress in understanding olfaction at the physiological level, attempts have been proposed to model our olfactory system with artificial devices

  • At about the same time as biochemical research was applied to olfaction with the discovery of odorant-binding proteins [1,2,3], the first attempt to mimic the human nose with an array of metal oxide-gas sensors was proposed [4]

  • After reviewing the information available on the physiological olfactory systems and the state-of-the-art on gas sensor technologies, we can return to our first question and ask what we still need to design an instrument capable of discriminating odours with performance similar to that of the human nose

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Summary

Introduction

Parallel to our progress in understanding olfaction at the physiological level, attempts have been proposed to model our olfactory system with artificial devices. At about the same time as biochemical research was applied to olfaction with the discovery of odorant-binding proteins [1,2,3], the first attempt to mimic the human nose with an array of metal oxide-gas sensors was proposed [4]. The designed systems range from individual gas sensors to complex arrays, incorporating inorganic, organic and biological sensing elements into electronic, optical and other types of devices [5,6,7]. After nearly four decades, despite the large amount of information currently available on the biochemical mechanisms of odour perception, and the tremendous advances in electronics and computing, we are still very far from designing a general-purpose instrument able to analyse complex mixtures of gases in the way the human nose does. When we look at specific problems and focused approaches, a large variety of solutions are being proposed, tailored to selected applications in the fields of food quality, environmental monitoring and clinical diagnostics [8,9,10,11,12,13]

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