Carbon dioxide sensors
are made as single-use sensors, measure contact-free and belong to the optical sensors 20. The sensors have a gas-permeable membrane and are based on a pH-sensitive dye in a HCO3--buffer solution. If CO2 is present in the culture broth, it diffuses through the gas-permeable membrane into the HCO3--buffer solution and changes its pH value. This is detected with the sensor and allows the pCO2 concentration to be determined afterwards using the Henderson-Hasselbach equation 20.