ARCHIVED - E-nose smells new applications

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September 01, 2011— Ottawa, Ontario

An NRC-designed “e-nose” sensor, intended to wirelessly detect formaldehyde off-gassing levels in airtight energy efficient “smart buildings,” is sniffing for further uses even before it goes to market.

The sensor, patented in early 2011, is based on a class of electricity conducting plastics called “conjugated polymers.” It was conceived after Health Canada issued new guidelines for formaldehyde exposure in indoor environments, such as tightly sealed buildings.

The monitor can detect carcinogenic formaldehyde gas at parts-per-billion levels. It’s quicker and more reliable than current commercial equipment, and can likely be improved to sense formaldehyde and other chemicals at even lower levels.

“The concept is based on very basic undergraduate chemistry — based on the reaction of aniline with formaldehyde. But it’s highly selective and sensitive,” says Dr. Gerardo Diaz-Quijada of the NRC Steacie Institute for Molecular Sciences in Ottawa. “The key advantages of this polymer is that the concept is very simple, and it’s very inexpensive to make. You don’t require fancy equipment and it has very fast response times — less than a fraction of a second. The most important advantage is that you can tailor the chemical structure of the polymer to sense other molecules of interest.”

Dr. Gerardo Diaz-Quijada (left) and Dr. Bhavana Deore examine a polymeric sensing element.

Dr. Gerardo Diaz-Quijada (left) and Dr. Bhavana Deore examine a polymeric sensing element.

This means that simply repainting different kinds of reactive coatings onto the same type of fingernail-sized electronic-backing hardware can alter the detector to monitor a whole range of molecules other than formaldehyde. A reactive coating responds to the presence of a specific molecule, and the backing layer electronically reads the change. 

The coatings can continuously monitor the levels of molecules for some time, because they react only briefly. And, several different sensors can be grouped together in one device to detect many molecules at once — a fact that led designers to take the concept further and build a more complex style of sniffer. 

How we smell chemicals

Most animals have hundreds of specific types of olfactory receptors, numbering in the millions, with each type having an affinity to a different class of chemical compound. Human brains recognize the patterns that these produce as different smells.  

“We figured we could make an artificial nose by mimicking these receptors using conjugated polymers with different affinities, then look at the patterns to identify compounds, in much the same way as we sense smell,” says Dr. Diaz-Quijada. 

The current e-nose is less sophisticated — and bigger — than most animals’ noses. But it proves the concept works, and can differentiate chemicals that have very similar molecular structures. The current lab prototype has just five sensors in a box the size of a computer tower, but Dr. Diaz-Quijada’s team is confident it can pack many more elements into a smaller package in the foreseeable future.

Early prototype for a five sensing-element e-nose

Early prototype for a five sensing-element e-nose

On-the-spot detectors

Dr. Diaz-Quijada says different forms of the e-nose platform can be adapted to printable electronics, like a form of molecular litmus paper, for quick use by emergency first responders and forensics investigators. Such devices could be used as on-the-spot detectors, or as dosimeter-type badges that can be checked later for accumulated exposure to a particular chemical or to nuclear radiation. This would enable a form of the detector that could be printed on a letter or parcel like an address label.  

“You could scan a package and tell if it has been exposed to a certain type of radiation during its journey,” he says. “Such technology for worldwide surveillance does not exist yet, but that would be the long-term goal.” 

At the moment, says Dr. Diaz-Quijada, licences for industry partners are being evaluated — a decision that will involve deciding which arrangements will best benefit long-term Canadian economic and development interests. An aircraft maker is interested in using this technology to monitor cabin air quality for various molecules of interest. And, in a post-9/11 world, the e-nose platform has also attracted regulatory, defence and security agencies, and related industries.

This diagram illustrates the e-nose concept. An air pump on the far left draws air and delivers it to the sensor array (four elements). The right side of the diagram depicts the pattern of responses obtained from all the sensing elements (each bar in the bar graphs represents the response of a single sensing element). The computer interprets the pattern (similar to a fingerprint) to identify the chemicals, in much the same manner that our brain processes olfactory information and identifies smells.

This diagram illustrates the e-nose concept. An air pump on the far left draws air and delivers it to the sensor array (four elements). The right side of the diagram depicts the pattern of responses obtained from all the sensing elements (each bar in the bar graphs represents the response of a single sensing element). The computer interprets the pattern (similar to a fingerprint) to identify the chemicals, in much the same manner that our brain processes olfactory information and identifies smells.

Related information

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National Research Council of Canada
613-991-1431
media@nrc-cnrc.gc.ca

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