Electronic Noses

An electronic nose (e-nose) is an intelligent sensing device that identifies and classifies the odor profile of vapors. Consisting of a sample-delivery unit, an array of gas sensors and a pattern recognition system, the instrument is designed to not only mimic but also improve upon the human olfactory sense, with its increased sensitivity and lack of subjectivity.

A typical e-nose will first transfer a sample into a sensor chamber to be conditioned under specified parameters, such as temperature and humidity. Inside the chamber, the sample is exposed to multiple gas sensors, which detect properties of the sample, such as mass, conductivity and capacitance. The sensors transmit these properties to a software program. Data analysis often relies on comparison to a software library of aroma signature patterns to determine the identity of the sample’s components.

The most common sensor types are metal oxide sensors, which use adsorption of gas molecules to measure conductivity. Other popular types include catalytic field effect sensors, which use an electronic field to determine molecular charge; quartz crystal microbalances and surface acoustic wave sensors, which measure mass change; conducting polymers, which measure change in electrical resistance; and optical sensors, which measure the modulation of light properties. Many e-noses work in tandem with analytical systems such as GC, MS and IR spectrometers.

Applications of e-noses usually involve product development, process monitoring and QC. In the food, fragrance and cosmetic industries, they are used to sense odors associated with product quality. E-noses are commonly used in the health care industry to detect molecules and microorganisms indicative of illness. For environmental purposes, they can monitor odors in wastewater treatment facilities and landfills. They can also be used in security applications to detect hazardous or explosive materials.

The leading supplier of e-noses is Alpha MOS, whose offerings include the GC-based HERACLES and ULYS models, and the GEMINI and FOX series of analyzers, which feature 6–18 different sensors. The company also distributes V&F’s AIRSENSE Analyzer, which employs soft-ionized MS. California-based Sensigent offers the Cyranose 320, a popular handheld e-nose, with software that can “learn” the chemical profile of vapors, allowing users to develop their own libraries. Another popular brand is Z-Nose, a series of GC-based benchtop and portable odor analyzers offered by Electronic Sensor Technology.

With annual sales of just over $25 million, the market for e-noses is projected to experience strong growth, particularly in the health care industry. As new applications are discovered, manufacturers are expected to develop models that are more compact, specialized, easier to use and less expensive.

Electronic Noses at a Glance:

Leading Suppliers

• Alpha MOS

• Electronic Sensor Technology

• Sensigent

Largest Markets

• Food and Beverage

• Environmental

• Research and Diagnostics

Instrument Cost

• $1,000–$100,000

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