Fluorescence plastic thin-film sensor for carbon dioxide

Abstract

The method of preparation of a novel plastic thin-film sensor that incorporates the fluorescent dye 8-hydroxypyrene-1,3,6-trisulfonic acid is described; the shelf-life of the film is over 6 months. The results of a study on the equilibrium response of the sensor towards different levels of gaseous CO₂ fit a model in which there is a 1 + 1 equilibrium reaction between the deprotonated form of the dye (present in the film as an ion pair) and the concentration of gaseous CO₂ present. In contrast to the situation in aqueous solution, in the plastic film the pK_a of the excited form of the dye appears close to that of the ground-state form, although this does not interfere with its use as a CO₂ sensor. The 0 to 90% response and recovery times of the film when exposed to an alternating atmosphere of air and 5% CO₂ are typically 4.3 and 7.1 s, respectively.