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Inspired by the powerful biological olfaction, scientists extracted numerous materials such as olfactory sensory neuron, olfactory receptor (OR) protein, and odorant binding protein from animal olfactory systems, then combined them with transducers to form multiple odor biosensors. These biosensors, despite well inheriting the sensing ability of creatures, have several drawbacks, such as complex preparation process, unstable sensing material characteristics, and high cost. Unlike the biological materials listed above, cell expressing heterologous OR maintains a stable sensing performance after passaging for multiple generations, also its experimental operation is simple, and cost is low. Therefore, odor biosensors based on cell expressing OR have been well developed in recent years. In this review, we first listed several odor biosensors based on cell expressing OR, mainly focusing on fluorescent and electrophysiological measurement methods. Furthermore, we illustrated the techniques to improve the biosensor performance, e. g., wider detection range, longer lifetime, more OR types, and higher quantification efficiency. In addition, we explained the possible prospects such as big sensor array and predicting odor response. [ABSTRACT FROM AUTHOR]

The Amperometric Gas Sensor (AGS) uses an electrode as the transducer element which converts its signal into a current from the electrochemical reaction of analytes taking place at the electrode surface. Many attempts to improve AGS performance, such as modifying the working electrode, applying a particular gas-permeable membrane, and selecting the proper electrolyte, etc., have been reported in the scientific literature. On the other hand, in the materials community, atomic gold has gained much attention because its physicochemical properties dramatically differ from those of gold nanoparticles. This paper provides an overview of the use of atomic gold in AGSs, both in a bulky AGS and a miniaturized AGS. In the miniaturized AGS, the system must be redesigned; for example, the aqueous electrolyte commonly used in a bulky AGS cannot be used due to volatility and fluidity issues. A Room Temperature Ionic Liquid (RTIL) can be used to replace the aqueous electrolyte since it has negligible vapor pressure; thus, a thin film of RTIL can be realized in a miniaturized AGS. In this paper, we also explain the possibility of using RTIL for a miniaturized AGS by incorporating a quartz crystal microbalance sensor. Several RTILs coated onto modified electrodes used for isomeric gas measurement are presented. Based on the results, the bulky and miniaturized AGS with atomic gold exhibited a higher sensor response than the AGS without atomic gold. [ABSTRACT FROM AUTHOR]

Replicating specific scents by mixing 'base odors' is the main idea behind the concept of odor reproduction. Just as primary colors can be combined to generate a wide range of colors in visual perception, the hope is to find a similar principle in olfaction. However, defining such 'primary odors' is difficult due to the complexity of our sense of smell, which is much different from vision. In spite of these challenges, numerous scientists have endeavored to identify a combination of basic smell components that can mimic various scents. Currently, the suggested combinations of smell components are typically only successful at recreating specific, intended scents. The range of reproducible scents differs based on the selection of base odors, yet these studies have provided valuable knowledge about the nature of these primary odors. This review paper will focus on the latest studies related to odor reproduction. Understanding odor space, odor reproduction, and the challenges encountered when expanding the range of odors will be explained. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]