Electronic nose
Encyclopedia
An electronic nose is a device intended to detect odor
s or flavor
s.
Over the last decade, “electronic sensing” or “e-sensing” technologies have undergone important developments from a technical and commercial point of view. The expression “electronic sensing” refers to the capability of reproducing human senses using sensor arrays and pattern recognition
systems.
Since 1982, research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction
and are performed for identification, comparison, quantification
and other applications, including data storage
and retrieval.. However, hedonic evaluation is a specificity
of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.
s, or by gas chromatography. The latter technique gives information about volatile organic compound
s but the correlation between analytical results and actual odor perception is not direct due to potential interactions between several odorous components.
In the Wasp Hound odor detector, the mechanical element is a video camera and the biological element is five parasitic wasps who have been conditioned to swarm in response to the presence of a specific chemical.
popularised the notion that it was difficult to
measure a smell, and in 1914 said the following:
In the decades since Bell made this observation, no such science of odor materialised, and it was not until the 1950s and beyond that any real progress was made.
Essentially the instrument consists of head space sampling, sensor array, and pattern recognition modules, to generate signal pattern that are used for characterizing odors.
Electronic noses include three major parts: a sample delivery system, a detection system, a computing system.
The sample delivery system enables the generation of the headspace (volatile compounds) of a sample, which is the fraction analyzed. The system then injects this headspace into the detection system of the electronic nose. The sample delivery system is essential to guarantee constant operating conditions.
The detection system, which consists of a sensor set, is the “reactive” part of the instrument. When in contact with volatile compounds, the sensors react, which means they experience a change of electrical properties. Each sensor is sensitive to all volatile molecules but each in their specific way.
Most electronic noses use sensor arrays that react to volatile compounds on contact: the adsorption
of volatile compounds on the sensor surface causes a physical change of the sensor. A specific response is recorded by the electronic interface transforming the signal into a digital value. Recorded data are then computed based on statistical models.
The more commonly used sensors include
In recent years, other types of electronic noses have been developed that utilize mass spectrometry or ultra-fast gas chromatography as a detection system.
The computing system works to combine the responses of all of the sensors, which represents the input for the data treatment. This part of the instrument performs global fingerprint analysis and provides results and representations that can be easily interpreted. Moreover, the electronic nose results can be correlated to those obtained from other techniques (sensory panel, GC
, GC/MS). Many of the data interpretation systems are used for the analysis of results. These systems include artificial neural network
(ANN), fuzzy logic
, pattern recognition modules, etc.
Various application notes describe analysis in areas such as flavor and fragrance, food and beverage, packaging, pharmaceutical, cosmetic and perfumes, and chemical companies. More recently they can also address public concerns in terms of olfactive nuisance monitoring with networks of on-field devices. Since emission rates on a site can be extremely variable for some sources, the electronic nose can provide a tool to track fluctuations and trends and assess the situation in real time. It improves understanding of critical sources, leading to pro-active odor management. Real time modeling will present the current situation, allowing the operator to understand which periods and conditions are putting the facility at risk. Also, existing commercial systems can be programmed to have active alerts based on set points (odor concentration modeled at receptors/alert points or odor concentration at a nose/source) to initiate appropriate actions.
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...
s or flavor
Flavor
Flavor or flavour is the sensory impression of a food or other substance, and is determined mainly by the chemical senses of taste and smell. The "trigeminal senses", which detect chemical irritants in the mouth and throat as well as temperature and texture, are also very important to the overall...
s.
Over the last decade, “electronic sensing” or “e-sensing” technologies have undergone important developments from a technical and commercial point of view. The expression “electronic sensing” refers to the capability of reproducing human senses using sensor arrays and pattern recognition
Pattern recognition
In machine learning, pattern recognition is the assignment of some sort of output value to a given input value , according to some specific algorithm. An example of pattern recognition is classification, which attempts to assign each input value to one of a given set of classes...
systems.
Since 1982, research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
and are performed for identification, comparison, quantification
Quantification
Quantification has several distinct senses. In mathematics and empirical science, it is the act of counting and measuring that maps human sense observations and experiences into members of some set of numbers. Quantification in this sense is fundamental to the scientific method.In logic,...
and other applications, including data storage
Data storage
Data storage can refer to:* Computer data storage; memory, components, devices and media that retain digital computer data used for computing for some interval of time....
and retrieval.. However, hedonic evaluation is a specificity
Specificity
Specificity may refer to:* Being specific * Specificity , the proportion of negatives in a binary classification test which are correctly identified...
of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.
Other techniques to analyze odors
In all industries, odor assessment is usually performed by human sensory analysis, by chemosensorChemosensor
A chemoreceptor, also known as chemosensor, is a sensory receptor that transduces a chemical signal into an action potential. In more general terms, a chemosensor detects certain chemical stimuli in the environment.- Classes :...
s, or by gas chromatography. The latter technique gives information about volatile organic compound
Volatile organic compound
Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and...
s but the correlation between analytical results and actual odor perception is not direct due to potential interactions between several odorous components.
In the Wasp Hound odor detector, the mechanical element is a video camera and the biological element is five parasitic wasps who have been conditioned to swarm in response to the presence of a specific chemical.
History
Scientist Alexander Graham BellAlexander Graham Bell
Alexander Graham Bell was an eminent scientist, inventor, engineer and innovator who is credited with inventing the first practical telephone....
popularised the notion that it was difficult to
measure a smell, and in 1914 said the following:
In the decades since Bell made this observation, no such science of odor materialised, and it was not until the 1950s and beyond that any real progress was made.
Working principle
The electronic nose was developed in order to mimic human olfaction that functions as a non-separative mechanism: i.e. an odor / flavor is perceived as a global fingerprint.Essentially the instrument consists of head space sampling, sensor array, and pattern recognition modules, to generate signal pattern that are used for characterizing odors.
Electronic noses include three major parts: a sample delivery system, a detection system, a computing system.
The sample delivery system enables the generation of the headspace (volatile compounds) of a sample, which is the fraction analyzed. The system then injects this headspace into the detection system of the electronic nose. The sample delivery system is essential to guarantee constant operating conditions.
The detection system, which consists of a sensor set, is the “reactive” part of the instrument. When in contact with volatile compounds, the sensors react, which means they experience a change of electrical properties. Each sensor is sensitive to all volatile molecules but each in their specific way.
Most electronic noses use sensor arrays that react to volatile compounds on contact: the adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
of volatile compounds on the sensor surface causes a physical change of the sensor. A specific response is recorded by the electronic interface transforming the signal into a digital value. Recorded data are then computed based on statistical models.
The more commonly used sensors include
- metal–oxide–semiconductor (MOSFET) devices - a transistor used for amplifying or switching electronic signals. This works on the principle that molecules entering the sensor area will be charged either positively or negatively, which should have a direct effect on the electric field inside the MOSFET. Thus, introducing each additional charged particle will directly affect the transistor in a unique way, producing a change in the MOSFET signal that can then be interpreted by pattern recognition computer systems. So essentially each detectable molecule will have its own unique signal for a computer system to interpret.
- conducting polymers - organic polymers that conduct electricity.
- quartz crystal microbalanceQuartz crystal microbalanceA quartz crystal microbalance measures a mass per unit area by measuring the change in frequency of a quartz crystal resonator. The resonance is disturbed by the addition or removal of a small mass due to oxide growth/decay or film deposition at the surface of the acoustic resonator...
- a way of measuring mass per unit area by measuring the change in frequency of a quartz crystal resonator. This can be stored in a database and used for future reference. - surface acoustic waveSurface acoustic wave]A surface acoustic wave is an acoustic wave traveling along the surface of a material exhibiting elasticity, with an amplitude that typically decays exponentially with depth into the substrate.-Discovery:...
(SAW) - a class of microelectromechanical systems (MEMS) which rely on the modulation of surface acoustic waves to sense a physical phenomenon.
In recent years, other types of electronic noses have been developed that utilize mass spectrometry or ultra-fast gas chromatography as a detection system.
The computing system works to combine the responses of all of the sensors, which represents the input for the data treatment. This part of the instrument performs global fingerprint analysis and provides results and representations that can be easily interpreted. Moreover, the electronic nose results can be correlated to those obtained from other techniques (sensory panel, GC
GC
- Education organizations :* Gordon College , an institution of higher education in Pakistan* Gordon College , an institution of higher education in Wenham, Massachusetts* Government College...
, GC/MS). Many of the data interpretation systems are used for the analysis of results. These systems include artificial neural network
Artificial neural network
An artificial neural network , usually called neural network , is a mathematical model or computational model that is inspired by the structure and/or functional aspects of biological neural networks. A neural network consists of an interconnected group of artificial neurons, and it processes...
(ANN), fuzzy logic
Fuzzy logic
Fuzzy logic is a form of many-valued logic; it deals with reasoning that is approximate rather than fixed and exact. In contrast with traditional logic theory, where binary sets have two-valued logic: true or false, fuzzy logic variables may have a truth value that ranges in degree between 0 and 1...
, pattern recognition modules, etc.
How to perform an analysis
As a first step, an electronic nose needs to be trained with qualified samples so as to build a database of reference. Then the instrument can recognize new samples by comparing volatile compounds fingerprint to those contained in its database. Thus they can perform qualitative or quantitative analysis. This however may also provide a problem as many odours are made up off multiple different molecules, this may be possibly wrongly interpreted by the device as it will register them as different compounds, resulting in incorrect or inaccurate results depending on the primary function of a nose.Applications
Electronic nose instruments are used by research and development laboratories, quality control laboratories and process & production departments for various purposes:In quality control laboratories for at line quality control such as
- Conformity of raw materials, intermediate and final products
- Batch to batch consistency
- Detection of contamination, spoilage, adulteration
- Origin or vendor selection
- Monitoring of storage conditions.
In process and production departments
- Managing raw material variability
- Comparison with a reference product
- Measurement and comparison of the effects of manufacturing process on products
- Following-up cleaning in place process efficiency
- Scale-up monitoring
- Cleaning in place monitoring.
Possible and future applications in the fields of health and security
- The detection of dangerous and harmful bacteria, such as software that has been specifically developed to recognise the smell of the MRSA (Methicillin-resistant Staphylococcus Aureus). It is also able to recognise methicillinsusceptible S. aureus (MSSA) among many other substances. It has been theorised that if carefully placed in hospital ventilation systems, it could detect and therefore prevent contamination of other patients or equipment by many highly contagious pathogens.
- The detection of lung cancer by detecting the VOC's (volatile organic compoundVolatile organic compoundVolatile organic compounds are organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and...
s) that indicate lung cancer. - The quality control of food products as it could be conveniently placed in food packaging to clearly indicate when food has started to rot.
- Nasal implants could warn of the presence of natural gas, for those who had anosmiaAnosmiaAnosmia is a lack of functioning olfaction, or in other words, an inability to perceive odors. Anosmia may be either temporary or permanent. A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one...
or a weak sense of smell.
Possible and future applications in the field of crime prevention and security
- The ability of the electronic nose to detect odourless chemicals makes it ideal for use in the police force, such as the ability to detect drug odours despite other airborne odours capable of confusing police dogs. However this is unlikely in the mean time as the cost of the electronic nose is too great and until its price drops significantly it is unlikely to happen.
- It may also be used as a bomb detection method in airports. Through careful placement of several or more electronic noses and effective computer systems you could triangulate the location of bombs to within a few metres of their location in less than a few seconds.
In environmental monitoring
- For identification of volatile organic compounds in air, water and soil samples.
- For environmental protection.
Various application notes describe analysis in areas such as flavor and fragrance, food and beverage, packaging, pharmaceutical, cosmetic and perfumes, and chemical companies. More recently they can also address public concerns in terms of olfactive nuisance monitoring with networks of on-field devices. Since emission rates on a site can be extremely variable for some sources, the electronic nose can provide a tool to track fluctuations and trends and assess the situation in real time. It improves understanding of critical sources, leading to pro-active odor management. Real time modeling will present the current situation, allowing the operator to understand which periods and conditions are putting the facility at risk. Also, existing commercial systems can be programmed to have active alerts based on set points (odor concentration modeled at receptors/alert points or odor concentration at a nose/source) to initiate appropriate actions.
See also
- Machine olfactionMachine olfactionMachine olfaction is the automated simulation of the sense of smell. It is an emerging requirement of modern robotics where robots or other automated systems are needed to measure the existence of a particular chemical concentration in air...
- Chemical field-effect transistor
- OlfactometerOlfactometerAn olfactometer is an instrument typically used to detect and measure ambient odor dilution. Olfactometers are used in conjunction with human subjects in laboratory settings, most often in market research, to quantify and qualify human olfaction. Olfactometers are used to gauge the odor detection...
- Electronic tongueElectronic tongueThe electronic tongue is an instrument that measures and compares tastes.Chemical compounds responsible for taste are perceived by human taste receptors, and the seven sensors of electronic instruments detect the same dissolved organic and inorganic compounds. Like human receptors, each sensor has...
- Fluctuation-enhanced sensingFluctuation-Enhanced SensingFluctuation-enhanced sensing is a specific type of chemical or biological sensing where the stochastic component, noise, of the sensor signal is analyzed...