A high performance, long-term, stable glucose sensor was developed and evaluated for continuous measurement of glucose for use in National Aeronautics and Space Administration space bioreactors while using a rotating wall perfused vessel system to support a baby hamster kidney (BHK-21) cell culture. The sensor employs a glucose oxidase multilayered membrane with a hydrogen peroxide electrode system. The output of the sensor was converted to glucose concentration utilizing the two-point calibration method. The sensor, tested over four 30 day bioreactor cell runs, showed a steady-state response time of less than 15 min. The sensor was able to measure glucose continuously and accurately for 16 days while using a single calibration and 30 days using two sets of calibrations, resulting in a standard error of prediction of ±0.5 normalmM as against a benchtop Beckman glucose analyzer. Evaluation conditions like cell culture pH, incubator temperature conditions, and operational flow rate, were found to have a very little effect on the sensor performance. © 2002 The Electrochemical Society. All rights reserved.

There is a need to monitor the concentration of dissolved oxygen (DO) present in the culture medium for NASA's space cell biology experiments, as well as in earth-based cell cultures. Continuous measurement of DO concentration in the cell culture medium in perfused bioreactors requires that the oxygen sensor provide adequate sensitivity and low toxicity to the cells, as well as maintain calibration over several weeks. Although there are a number of sensors for dissolved oxygen on the market and under development elsewhere, very few meet these stringent conditions. An in-house optical oxygen sensor (HOXY) based on dynamic fluorescent quenching of Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) chloride and a pulsed blue LED light source was developed in our laboratory to address these requirements. The sensing element consisted of the fluorescent dye embedded in a silicone matrix and coated onto a glass capillary. Photobleaching was minimized by a pulsed LED light source. The total noise in the sensor output is 2% and the sensor dynamic range is 0 to 200 mm Hg. The resolution of the sensor is 0.1 mm Hg at 50 mm Hg, and 0.25 mm Hg at 130 mm Hg, while the accuracy is 5%. The LED-based oxygen sensor exhibited stable performance and low drift, making it compatible for space-flight bioreactor systems.

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