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Background: Compact and automated sensors are desired for assessing the health of cell cultures in biotechnology experiments. While several single-analyte sensors exist to measure culture health, a multi-analyte sensor would simplify the cell culture system. One such multi-analyte sensor, the Paratrend 7 manufactured by Diametrics Medical, consists of three optical fibers for measuring pH, dissolved carbon dioxide (pCO2), dissolved oxygen (pO2), and a thermocouple to measure temperature. The sensor bundle was designed for intra-vascular measurements in clinical settings, and can be used in bioreactors operated both on the ground and in NASA’s Space Shuttle and International Space Station (ISS) experiments. Methods: A Paratrend 7 sensor was placed at the outlet of a bioreactor inoculated with BHK-21 (baby hamster kidney) cells. The pH, pCO2, pO2, and temperature data were transferred continuously to an external computer. Cell culture medium, manually extracted from the bioreactor through a sampling port, was also assayed using a bench top blood gas analyzer (BGA). Results: Two Paratrend 7 sensors were used over a single cell culture experiment (64 days). When compared to the manually obtained BGA samples, the sensor had good agreement for pH, pCO2, and pO2 with bias (and precision) 0.005(0.024), 8.0 mmHg (4.4 mmHg), and 11 mmHg (17 mmHg), respectively for the first two sensors. A third Paratrend sensor (operated for 141 days) had similar agreement (0.02±0.15 for pH, −4±8 mm Hg for pCO2, and 24±18 mm Hg for pO2). Conclusion: The resulting biases and precisions are com- parable to Paratrend sensor clinical results. Although the pO2 differences may be acceptable for clinically relevant measurement ranges, the O2 sensor in this bundle may not be reliable enough for the ranges of pO2 in these cell culture studies without periodic calibration. [ABSTRACT FROM AUTHOR]