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

Biomedical Microdevices 7:3, 197204, 2005C 2005 Springer Science + Business Media, Inc. Manufactured in The Netherlands.A Miniaturized Carbon Dioxide Gas Sensor Based on Sensing

of pH-Sensitive Hydrogel Swelling with a Pressure SensorS. Herber, J. Bomer, W. Olthuis, P. Bergveld, andA. van den BergUniversity of Twente, Faculty of Electrical Engineering, Mathematics

& Computer Science, Laboratory of Biosensors, P.O. Box 217,7500 AE Enschede, The NetherlandsE-mail: [email protected]. 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 37C. 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.KeyWords. CO2, Pco2, carbon dioxide, hydrogel, pH-sensitive, pressure, sensorIntroductionThe detection and continuous monitoring of carbon dioxide is becoming increasingly important in various application areas such as global environmental monitoring (Baird,

1995), horticulture (Adams et al., 1984), indoor climate

controle (Erdmann, et al., 2002) and the medical field

(Davenport, 1974). One particularly interesting medical

application is the quantification of partial pressure of carbon dioxide (Pco2) in the stomach to diagnose gastrointestinal ischemia (Groeneveld and Kolkman, 1994; Otte

et al., 2001; Kolkman et al., 2000, 1997). This type of ischemia occurs when blood flow is insufficient to deliver

oxygen and nutrients to the stomach and intestines. The

insufficient blood flow may be caused by occlusion of

arteries or veins, or by general circulatory failure. A consequence of gastrointestinal ischemia is an unusually high

partial pressure of carbon dioxide (Pco2) in the intestines

and stomach. This Pco2 can be measured and used for diagnosis. In case of ischemia, gastric carbon dioxide levels

can range from 3 to 20 kPa CO2.At present, air tonometry is used to measure the

partial pressure...