A personal device for analyzing carbon dioxide in real time and real breath: Experimental investigation and computational simulation

A novel real-time carbon dioxide analyzer for health and environmental applications

“…Note that several differences are stayed in the present work with respect to previous work [24]. Regarding the sensor: a - The sensor substrate uses a fluorinated hydrophobic membrane instead of transparent polyethylene-based plastic; b- The hydrophobic membrane has microstructures and surface properties that provide faster water desorption and significantly improved sensor time response; c- The new indicator, m-cresol purple, provides a wider dynamic range of CO 2 % concentration due to its lower pka.…”

“…The colorimetric CO 2 sensor presented in this paper was prepared by coating a sensor chip with a solution containing HCO 3 − /CO 3 2− buffer and m- cresol purple as the sensing element [19, 24]. All the reagents used in this work were analytical grade and purchased from Sigma-Aldrich (St. Louis, MO, USA).…”

“…All the reagents used in this work were analytical grade and purchased from Sigma-Aldrich (St. Louis, MO, USA). As described in our previous work, when an ambient air sample or warm breath sample was brought into contact with the sensor chip, the pH of the sensing material decreased, which led to a color change [24]. This color change was detected with an optoelectronic detection system (see details below).…”

“…Regarding the sensor: a - The sensor substrate uses a fluorinated hydrophobic membrane instead of transparent polyethylene-based plastic; b- The hydrophobic membrane has microstructures and surface properties that provide faster water desorption and significantly improved sensor time response; c- The new indicator, m-cresol purple, provides a wider dynamic range of CO 2 % concentration due to its lower pka. Compared with thymol blue [24], m- cresol purple changes color more sensitively under weakly alkaline to neutral conditions (pH value: 9.0 – 6.0), which typically corresponds to the range of normal breath CO 2 levels (1.0% – 11.5%) [25 – 27] (Fig. 1).…”

“…The device features a colorimetric sensor that could analyze breath CO 2 concentration accurately, and a fluidic system for efficient delivery of breath sample to the sensing element. A 3D model was created to simulate the sample flow and reaction of CO 2 with the sensing materials and color changes associated with the chemical reactions [24]. Despite the success, the sensor response was slow and semi-reversible, which is not suitable for breath-by-breath CO 2 analysis as needed for capnography, and moreover, which is insensitive to real-time monitoring of CO 2 in air.…”