Modification of a piezo-optical gas dosimeter system towards continuous gas sensing: a feasibility study with carbon dioxide

We report a feasibility study of monitoring gases continuously by means of an adapted piezo-optical dosimeter system. The test gas is carbon dioxide whose presence is detected via a pH indicator colour change. Sensing spots consist of m-Cresol Purple supported in a buffered ethyl cellulose matrix and deposited on an indium-tin oxide coated piezoelectric film. The change in absorbance is measured via illumination with an amber LED whose peak emission at 592 nm corresponds to the basic form of the reagent. A sensor was developed and calibrated over the range 0–2.5% CO₂ of interest for personal monitoring. The 90% response times are 3–4 min but the response rates could be used to trigger an alarm in the first few seconds of CO₂ increase.