Applying Odor Preconcentrator for Enhancing Human Olfaction: Feasibility Study
Authors: Tsukada Yosuke , Kawai Takumi , Matsukura Haruka , Ishida Hiroshi 
Published: July 2021

Introduction

The human sense of smell plays important roles in various scenes in everyday life although we are unconscious of its importance in most cases. For example, olfaction provides alerts that lets us notice dangers or risks such as a fire and rotten food. Savory food smells and comfort flower fragrances make our lives richer. However, it is known that the human olfaction deteriorates with our age [1]. There is no device that can improve the deteriorated olfaction whereas impaired vision can be improved using eyeglasses and a hearing aids can improve our audition. The aim of this research project is to develop an olfactory amplifier for humans [2,3]. In chemical analysis, preconcentrators are frequently used to analyze faint chemical substances [4]. We propose to apply this technique to enhance the sensitivity of human olfaction. In the proposed olfactory amplifier system, airborne odor molecules are collected into adsorbent, as in the preconcentrator. When a sufficient amount of odor molecules are collected, the adsorbent is heated to a high temperature to thermally desorb the collected molecules in a short time. The concentrated odors are thus generated. Here we report our new device made with a monolithic silica adsorbent. Results of an odor concentration experiment and a sensory test are presented to show that the device can generate a clearly perceivable smell from a faint smell sample.

Method

The schematic diagram of our new device that uses a disc-shaped monolithic silica (MonoTrap DSC18, GL Science) as an adsorbent is shown in Figure 1. The cross section of the device is shown in Figure 2. The diameter and thickness of the monolithic silica disk are 10 mm and 1 mm, respectively. This adsorbent is housed in a flow cell which was made by putting a rubber sheet with a hole in the middle between an acrylic plate and a printed circuit board. A meander heater made on the printed circuit board is used for thermally desorbing the collected odor molecules from the monolithic silica disk. Five stainless-steel tubes are attached to the flow cell. Air is sent into the flow cell through the center tube, and is exhausted from the four outer tubes.
In the odor concentration experiment, 1.2 ppm 1-butanol vapor packed in a sampling bag was sent into the flow cell at a flow rate of 0.8 L/min for 10 min. The collected butanol molecules were desorbed by heating up the monolithic silica to 200 degrees centigrade. Clean air was sent to the flow cell at a flow rate of 20 mL/min to take the concentrated odor vapor out from the flow cell. The concentration of the butanol vapor presented from the device was measured using a semiconductor gas sensor (TGS2620, Figaro Engineering). In the sensory test, we prepared liquid apple flavor consisting of nine components. The flavor was diluted by 100 times using liquid paraffin. Eight subjects participated in the sensory test. Each subject was asked to sniff the diluted apple flavor and compare its smell with the smell of the concentrated vapor presented from the odor amplifier device.

Results and Discussions

Figure 3 shows the response curves of the gas sensor which was exposed to the vapor coming out from the odor amplifier device. The sensor response is defined as the ratio of the sensor resistance in gas to that in air. Its value decreases with the gas concentration. At 20 s from the start of recording the sensor response, the heater was turned on. The pump was activated after 4 s delay from the activation of the heater. The concentration factor calculated from the maximum butanol concentration detected by the gas sensor was 13.1. When the delay was reduced to 0 s, the concentration factor was slightly decreased. Table 1 shows the result of the sensory test. All subjects answered that the vapor presented from the amplifier device had a stronger smell and that the difference in the smell intensity was significant. Seven out of eight subjects even told us that they perceived no smell from the diluted liquid apple flavor. Most subjects told us that the original and concentrated smells were different because they were unable to perceive the original smell. These results show that a sufficient odor amplification effect can be obtained by a concentration factor of approximately 10. Future work will be addressed to enable quicker presentation of concentrated odors. This work was supported in part by JSPS KAKENHI Grant Numbers 19K14947 and 19H02103, and Research Grant from the Okawa Foundation for Information and Telecommunications.

References

[1] A.S.Mobley, D.J.Rodriguez-Gil, F.Imamura, C.A.Greer, Agin in the olfactory system, Trends in Neurosciences. 37 (2014) 77–84. doi:10.1016/j.tins.2013.11.004.
[2] H.Masukura, H.Ishida, Review on development of devices for amplifying human olfaction: Approaches using real and virtual concentration method, Electronic and Communication in Japan. 102 (2019) 55–60. doi:10.1541/ieejsmas.138.337.
[3] H.Matsukura, K.Takayasu, H.Ishida, Devices for assisting human olfaction: Some fundamental experiments, Procedia Chemistry. 20 (2016) 60–62. doi:10.1016/j.proche.2016.07.010.
[4] J.Lee, S.-H.Lim, CNT foam-embedded micro gas preconcentrator for low-concentration ethane measurements, Sensosrs. 18 (2018) 1547. doi:10.3390/s18051547.

Figure 1