Local detection of gaseous carbon dioxide using optical fibers and fiber tapers of single-cell dimensions

Abstract

The CO2 amount in the air and its monitoring is widely recognized as an important issue at this time. We are facing excessive CO2 production and global warming affecting not only the environment but also life at the lowest level. A variety of strategies have been designed to reduce atmospheric CO2, but one promising method is based on the application of biologically engineered microorganisms to actively consume a high volume of CO2. The paper presents the design, development, and characterization of two types of sensors for the local detection of gaseous carbon dioxide on microscopic scale. The first one was designed as a fiber optic CO2 measuring cell and the second was based on a CO2 sensitive fiber taper tip. The sensors were based on the absorption of guided visible light in a sensitive polymer layer. The sensors were characterized in the range of 0%-10.6% of carbon dioxide concentration with full linearity. A sensitivity of 0.25 +/- 0.05 dB/% and a limit of detection of 7.1.10(-3)% have been determined for the sensing element. We have experimentally verified the operational reversibility of the CO2 sensing element over time. The time response of the sensor with the finally used sensitive layer of thickness of 600 nm was one second. Both sensors were designed for future application in biological research. Especially the second type of the sensor based on 3 mu m silica glass taper tip (diameter corresponding to single-cell proportions) is suitable for laboratory testing of microorganisms and cells that actively consume gaseous carbon dioxide.