Real-time dissolved carbon dioxide monitoring I: Application of a novel in situ sensor for CO 2 monitoring and control

Dissolved carbon dioxide (dCO ) is a well-known critical parameter in bioprocesses due to its significant impact on cell metabolism and on product quality attributes. Processes run at small-scale faces many challenges due to limited options for modular sensors for online monitoring and control. Traditional sensors are bulky, costly, and invasive in nature and do not fit in small-scale systems. In this study, we present the implementation of a novel, rate-based technique for real-time monitoring of dCO in bioprocesses. A silicone sampling probe that allows the diffusion of CO through its wall was inserted inside a shake flask/bioreactor and then flushed with air to remove the CO that had diffused into the probe from the culture broth (sensor was calibrated using air as zero-point calibration). The gas inside the probe was then allowed to recirculate through gas-impermeable tubing to a CO monitor. We have shown that by measuring the initial diffusion rate of CO into the sampling probe we were able to determine the partial pressure of the dCO in the culture. This technique can be readily automated, and measurements can be made in minutes. Demonstration experiments conducted with baker's yeast and Yarrowia lipolytica yeast cells in both shake flasks and mini bioreactors showed that it can monitor dCO in real-time. Using the proposed sensor, we successfully implemented a dCO -based control scheme, which resulted in significant improvement in process performance.