PHASE FLUOROMETRIC OPTICAL CARBON-DIOXIDE GAS SENSOR FOR FERMENTATIONOFF-GAS MONITORING

We demonstrated an optical carbon dioxide gas sensor suitable for repl acement of gas chromatographs and mass spectrometers for the measureme nt of carbon dioxide in the off-gas of a bioreactor for fermentation a nd cell culture applications. The sensor is based upon the change in l ifetime of a donor fluorophore, sulforhodamine 101 (SR101), induced by fluorescence resonance energy transfer to a pH-sensitive, nonfluoresc ent acceptor, m-cresol purple (MCP). Carbon dioxide diffusing into the sensor produces carbonic acid, changing the absorbance spectrum of th e MCP, and thus its spectral overlap with the SR101, changing its life time. This lifetime change was measured in the frequency, rather than the time domain, as a change in the phase angle of the fluorescence re lative to the modulated excitation light. The sensor was calibrated by correlating the phase response to carbon dioxide concentrations. The calibration remained valid over the life of the sensor, which has been shown to be greater than 2 weeks. The sensor was most sensitive at lo w CO2 concentrations and responded to concentration changes in seconds . The sensor film is very inexpensive to produce and the light source is an inexpensive light-emitting diode. Furthermore, lower cost detect ion electronics can be developed since only one modulation frequency i s required. In addition, this sensor can potentially be used in vivo, with a fiber optic both delivering the excitation light and collecting the emission.