Editorial Feature

Sensing the Human Body: Olfaction with an Electronic Nose

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The interaction between an olfactory epithelium and an odor stimulus determines olfaction. A mucous layer is found below an olfactory membrane, which is present in a nasal cavity. The membrane also consists of receptor cells for sensing odors. The impulses are transmitted to an olfactory bulb located at a lower part of the front brain through the receptor cells. It is estimated that humans contain nearly 100 million receptors cells.

The criteria for receptor cells to detect the odor of a substance are set out below:

  • Contact between at least a few odorous particles and receptors for a short interval.
  • As olfactory cilia are essentially lipid material, the substance must be soluble in lipid molecules.
  • The substance should be slightly soluble in water to pass to the olfactory cells via the mucous layer.
  • In order to penetrate the air in a sensory area, a volatile substance is required.
  • The odor mechanism can be described using two theories - physical theory and chemical theory. The physical theory states that odor perception can be facilitated based on the odorant molecule’s shape, which determines if the olfactory cells are to be activated. Conversely, the chemical theory suggests that chemical binding of the odorant molecules to the receptors produces a receptor potential that in turn creates impulses in the nerve fibers of olfactory cells. The physiological mechanisms to olfaction have helped inspire the development of an electronic nose for the detection of flavors and odors.  

Basic Principle

An electronic nose is a device designed for detecting flavors and odors by imitating human olfaction mechanism. It consists of three functional components: computing system, a detection system and a sample delivery system.

The sample delivery system creates a sample headspace which is later analyzed in fraction. The headspace is introduced into the detection system via the delivery system. A set of sensors considered as the instrument's "reactive" part is present inside the detection system. A change in the electrical properties of the sensors takes place when the sensor-arrays present in the sensors come in contact with the headspace. This change is due to the adsorption of the headspace by a sensor surface.

Meanwhile, an electronic interface records a specific response. The signals are digitalized, and the recorded information is computed with respect to the statistical models. The responses from all the sensors are combined by the computing system to provide inputs for the data treatment. In addition, a global fingerprint analysis is carried out by the computing system to yield results that can be interpreted easily.

Currently available electronic noses make use of techniques such as ultra-fast gas chromatography or mass spectrometry in detection systems.

Research

An electronic nose is a device designed for detecting flavors and odors by imitating the human olfaction mechanism. It consists of three functional components: a computing system, a detection system and a sample delivery system.

The sample delivery system creates a sample headspace which is later analyzed in fraction. The headspace is introduced into the detection system via the delivery system. A set of sensors considered as the instrument's "reactive" part is present inside the detection system. A change in the electrical properties of the sensors takes place when the sensor arrays come into contact with the headspace. This change is due to the absorption of the headspace by a sensor surface.

Meanwhile, an electronic interface records a specific response. The signals are digitalized, and the recorded information is computed with respect to the statistical models. The responses from all the sensors are combined by the computing system to provide inputs for the data treatment. In addition, a global fingerprint analysis is carried out by the computing system to yield results that can be interpreted easily.

Currently available electronic noses make use of techniques such as ultra-fast gas chromatography or mass spectrometry in detection systems.

Application of the Electronic Nose in the Detection of Changes in Airway for Asthma Sufferers

In 2010, Lazar Z carried out an experiment to emphasize that electronic nose breathprints obtained from asthmatic patients are free of acute changes occurring in the airway caliber. During the experiment, 10 asthmatic patients were made to undergo a methacholine provocation test (Visit 1) followed by a sham challenge test using isotonic saline (Visit 2). The results revealed a fall of 1 second in forced expiratory volume (FEV) by 30.8 ± 3.3% due to methacholine inhalation along with certain variations in breathprint. Although saline inhalation had varied breathprints, it did not alter FEV 1. Therefore, the experiment demonstrated that nebulized aerosols change the molecular profile of exhaled air in asthmatic patients without causing acute changes in airway caliber.

Future Direction for the Electronic Nose in Medical Application

The biomedical industry is developing rapidly with the use of advanced sensor systems by companies that develop diagnostic equipment. Researchers hope that epidemic diseases like autoimmune deficiency syndrome, tuberculosis and others can be efficiently managed by the combination of intelligent e-nose sensors, advanced satellite communication systems and information technology. As a result, new interfaced or tandem systems can evolve for diagnostic and biomedical applications.

Pattern recognition algorithms of e-nose technologies are already used for detecting the exposure to toxins in smoking and categorizing limb artery disease. In addition, e-nose technologies are currently being used with mechanical as well as chemical detection devices, for example, electronic tongues, neurochips and biosensors. Hence, future applications of e-noses and e-nose tandem devices in the healthcare industry are likely to increase.

However, one main drawback of using e-nose devices in medical applications is the inability to determine the performance, feasibility and capabilities of the devices within medical facilities. The lack of interest from medical services personnel to replace traditional methods with novel technologies has also hindered the use of e-nose technology in the medical field. Another difficulty is to find a specific, feasible biomedical application, which can be achieved only through regular inputs from the physicians. Once these issues are fixed, e-nose technology can offer much more effective solutions for the medical industry.

Sources and Further Reading

  • Wilson A.D, Baietto M. Advances in Electronic-Nose Technologies Developed for Biomedical Applications. Sensors. 2011; 11: 1105–1176.
  • Lazar Z, Fens N, Maten J, Schee M.P, Wagener A.H, Nijs S.B, Dijkers E, Sterk P.J. Electronic Nose Breathprints Are Independent of Acute Changes in Airway Caliber in Asthma. Sensors. 2010; 10: 9127–9138.
  • Machado R.F, Laskowski D, Deffenderfer O, Burch T, Zheng S, Mazzone P.J, Mekhail T,  Jennings C, Stoller J.K, Pyle J. Detection of Lung Cancer by Sensor Array Analyses of Exhaled Breath. Am J Respir Crit Care Med. 2005; 171:1286–1291.

This article was updated on 14th February, 2020.

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