Electronic Nose

Principle Of E-Nose

Mimicking the nose is a challenging task. The human nose can smell 10,000 different odour molecules mixed in air. Odour in a substance is due to certain volatile organic compounds (VOCs), which easily evaporate and get carried by an air stream. An e-nose can smell and estimate odours quickly though it has little or no resemblance to the human nose. A human nose has receptors, which serve as binding sites for VOCs. A receptor is just a molecular structure on the surface of the nerve cell to which an odorous molecule with the right shape binds. The receptor and the binding molecule fit exactly as in a key and lock arrangement. These odour-sensing nerve cells line the upper part of the cavity in the human nose. Once an odour molecule binds to a receptor, a chain reaction follows which ultimately transmits an electrical signal to the brain. A specific odour of coffee or wine is usually caused not by one, but a mixture of hundreds of organic compounds. So, the brain has a mammoth task of processing signals received from the nerve cells originating from the nose, to identify the nature of smell. The exact working of the brain in processing these signals is yet to be fully understood.

 Abstract

        In an ever-developing world, where electronic devices are duplicating every other sense of perception, the sense of smell is lagging behind. Yet, recently, there has been an urgent increase in the need for detecting odours, to replace the human job of sensing and quantification.

Nose on a Chip

When he arrives home from vacation, Clarence’s smart alarm system deluges him with messages. Natural gas is leaking from the furnace. Smoke is present in a guest bedroom. Food is spoiling in the refrigerator. In the garage, a paint can lid apparently has come loose, and a container of insecticide is leaking. Such a warning capability may be possible someday, thanks to ORNL’s invention of a “nose on a chip.” This wireless electronic nose can simultaneously detect and measure a variety of vapors in the air and signal a receiver to sound an alarm or display a message. Already tests of this first battery-operated cantilever array sensor chip set have shown it can simultaneously sense various combinations of hydrogen, nitric oxide, mercury vapor, and alkane thiols in the air. Because the device is inexpensive and can provide instant results, it could soon be incorporated into household gas appliances to warn of hazardous leaks.

Introduction

 In the past decade, electronic nose instrumentation has generated much interest internationally for its potential to solve a wide variety of problems in fragrance and cosmetics production, food and beverages manufacturing, chemical engineering, environmental monitoring, and more recently, medical diagnostics and bioprocesses. Several dozen companies are now designing and selling electronic nose units globally for a wide variety of expanding markets. An electronic nose is a machine that is designed to detect and discriminate among complex odours using a sensor array. The sensor array of consists of broadly tuned (non-specific) sensors that are treated with a variety of odour-sensitive biological or chemical materials. An odour stimulus generates a characteristic fingerprint (or smell-print) from the sensor array. Patterns or fingerprints from known odours are used to construct a database and train a pattern recognition system so that unknown odours can subsequently be classified and identified. Thus,electronic nose instruments are comprised of hardware components to collect and transport odours to the sensor array – as well as electronic circuitry to digitise and stored the sensor responses for signal processing.