From Gas Sensors to Biomimetic Artificial Noses

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.

The Emergence of Insect Odorant Receptor-Based Biosensors

“…In different studies, microelectrodes were used to record signals from olfactory receptor neurons of blowfly in a setup similar to patch clamp electrophysiological measurements [39]. Vertebrates and insect OBPs consist of two distinct families of structurally compact proteins that carry hydrophobic odorant molecules from the gas phase to the respective membrane-bound receptor across an aqueous environment [40]. The use of OBPs as soluble tethered biorecognition elements has also been demonstrated.…”

A Perspective on Recent Advances in Piezoelectric Chemical Sensors for Environmental Monitoring and Foodstuffs Analysis

“…An analysis of publication activity over the past 20 years in international peer-reviewed journals, in this and previous reviews [1,7,[9][10][11][12][13][14]108], the number of abstracts at major conferences dedicated not only to sensorics, but also in the area technology and information, all this allows objectively assess the relevance and interest of the scientific community public consumers to development, production and implementation for wide range of applications the analyzers based on chemical sensors of various principles, including piezo quartz microbalances.…”

“…In particular, special attention is given to sensors' mechanical robustness, chemical inertness, parameter independence on external conditions (positioning in space, temperature, and pressure), selectivity, sensitivity, possibility of automation, size, and cost. Previously, several comprehensive books and reviews on chemical sensors and sensor array principles and applications were published [3][4][5][6][7][8][9][10][11][12][13]. Nowadays, oscillatory-based sensory systems cover a significant part of the total number of sensors employed [1,[14][15][16][17].…”

Odorant-Binding Proteins as Sensing Elements for Odour Monitoring

“…The need for information about the biological system is essential when designing an electronic nose, defined as an analytical instrument capable of discriminating odours using an approach similar to the one realized in our olfactory system. Aspects related to the olfactory code and strategies currently adopted to decipher the language of smell have been already discussed in a recent review [ 11 ]. Therefore, here we focus on the choice of sensing elements and suggest, on the basis of several experimental aspects, that proteins, in particular soluble binding proteins of olfactory systems, could qualify as suitable detecting elements for artificial gas and smell sensing.…”

“…It is worth emphasizing at this point that, although binding proteins appear as the most promising biosensing elements, sensitivity remains probably the main issue in artificial olfaction. Taking as a reference the human nose (which is a poorly performing system when compared to olfaction in insects [ 3 ] and also in other mammals), the most sophisticated devices are still orders of magnitudes far from the desired goal [ 11 ]. To fill such a gap we need new approaches, rather than more sophisticated amplifiers.…”