Detection of volatile organic compounds by an interferometric sensor

In the present work the development of an interferometric gas sensor to detect volatile organic compounds (VOCs) is presented. A polydimethylsiloxane (PDMS) sensing film was deposited on a glass substrate. PDMS has the property of swelling and/or change its refractive index when it interacts with VOCs. This causes a fringe shift in a Pohl interferometric arrangement. Such fringe shift was measured by a conventional photodetector. The results showed that the sensor response was almost linear in the concentration range of 0–24,000 ppm for ethanol. The sensor responses for other VOCs were also measured. From measurements and calculations it was found that the sensor response characteristics are determined essentially by the swelling effect more than the refractive index change. Therefore it could be said that the sensor response is related to the volume of the VOC molecule.