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Measuring Indoor Air Quality

Isabelle Dufour, researcher at IXL(1) in Talence has developed an air analysis system that works in real time. In 2005, Ademe(2) awarded her the Innovative Environmental Techniques Prize for this work. She explains why this concept is important, how it works, and how it may develop in the future.



© Illustration : S. Kiehl

What public health problem are you trying to find a solution to?

Isabelle Dufour: Air quality has become a major concern for society. We now know that air inside apartments and buildings is often polluted, especially by volatile organic compounds (VOCs). These compounds cause numerous health problems such as cancers, asthma, or neurological damage. About fifty of these molecules can frequently be found in common places. Take carpets, or doors and furniture made of chipboard, for example; they are produced using solvents that then make their way into the air we breathe. Today, if you want to detect VOCs and measure their concentration, you have to take air samples and analyze them in a lab, a process that can take several days. Our aim is to produce a generic detector that works  non-stop and  gives accurate readings in real time.


What principle is this detector based on?

ID: It relies on the use of silicon microbeams that are about one millimeter long and a few micrometers thick. Each one is covered with a different sensitive coating which selectively captures the target molecules. When these target molecules are captured by the microbeams, the mass of the microbeams is altered, which results in a change in their resonance frequency. It's this frequency, measured in real time by an electronic device, that can give us information about the presence and concentration of the target molecules. The advantage is that it's a compact, self-contained system that puts out a signal that can easily be interpreted.


What are these sensitive coatings made of?

ID: They're made of polymers. One of the requirements is that the bonding with the VOC should be reversible. There's a thermodynamic equilibrium: If you renew the air and the molecule is no longer present, the system knows it. In order to design the sensitive coatings, we worked with chemists, in particular at the European Membrane Institute in Montpellier,3 and we asked them to develop new, more selective materials which target new species.


Are you thinking of setting up a company to market this system?

ID: To be honest, research is still at too early a stage for us to be thinking about marketing this product. For the moment, we are attempting to optimize our results and lower the detection limits as much as possible. I believe that in a few years' time, the process will be operational. Maybe at that time, one of our PhD students will be interested. The system would let us monitor air quality in key locations such as factories or public places. In the subway, this process could be part of a security system against chemical attacks. However, my real dream is that a device like this becomes as common as a thermometer, barometer, or mini weather station.


Sebastián Escalón

Notes :

1. Laboratoire d'études de l'intégration des composants et systèmes électroniques (Laboratory for the Study of Integration of Electronic Components and Systems. CNRS / Enseirb / Université Bordeaux-I joint lab).
2. Agence de l'Environnement et de la Maîtrise de l'Energie (French Agency for Environment and Energy Management).
3. Institut Européen des membranes (IEM) (CNRS / Université Montpellier-II / Ecole nationale supérieure de chimie de Montpellier joint lab).

Contacts :

Isabelle Dufour
Laboratoire IXL, Talence.


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