A Miniaturized Carbon Dioxide Gas Sensor Based on Sensing of pH-Sensitive Hydrogel Swelling with a Pressure Sensor

A measurement concept has been realized for the detection of carbon dioxide, where the CO₂ induced pressure generation by an enclosed pH-sensitive hydrogel is measured with a micro pressure sensor. The application of the sensor is the quantification of the partial pressure of CO₂ (Pco₂) in the stomach as diagnosis for gastrointestinal ischemia. The principle is put to the proof by examining the sensor response to changes in Pco₂. Furthermore, the response time, temperature-sensitivity and resolution are determined. The sensor responds well to changes in Pco₂ with a maximum pressure generation of 0.29× 10⁵ Pa at 20 kPa CO₂. The 90% response time varies between 1.5 and 4.5 minutes at 37^∘C. The sensor shows a linear temperature-sensitivity which can easily be compensated for, and enables detection of Pco₂ changes as small as 0.5 kPa CO₂.