Process analytical technologies that can operate in sterile environments are needed for in-line monitoring of biopharmaceutical manufacturing processes.  Sensors that can be sterilized with disposable bioreactors and other single-use systems are of particular interest but must perform reliably over several weeks while remaining cost-effective.  We find that solid-state (thin-film) potentiometric electrodes printed on thermoplastic substrates can be subjected to sterilizing γ-radiation without loss of stability or performance over many weeks, using pH as the benchmark analysis. Working electrodes that are exposed to γ-radiation and stored in phosphate buffer can maintain Nernstian sensitivity over 100 days, and exhibit a voltage decay that is stable but of opposite sign to untreated controls. The long-term potential drift of γ-irradiated pH electrodes is less than +0.3 mV (0.005 pH) per day; γ-irradiated reference electrodes are also stable over time and inert to changes in pH and ionic strength.  The γ-irradiated electrodes can monitor pH changes in cell culture media within 0.1 units relative to a commercial meter after a single-point calibration. The thin-film electrode designs can be reproduced using semi-automated manufacturing methods, which is essential for device reproducibility.

Radiation-tolerant solid-state potentiometric electrodes: Design, performance, and manufacturing

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