Fiber-optic microsensors with a tip diameter of approximately 140 microm have been developed that enable simultaneous measurement of dissolved oxygen (DO) and pH, and of DO and temperature (T), respectively. The tip of the optical fiber was covered with sensor compositions based on luminescent microbeads that respond to the respective parameters by a change in the decay time, intensity of their luminescence, or both. The use of microbeads enables the ratio of the signals to be easily varied, reduces the risk of fluorescence energy transfer between indicator dyes, and reduces the adverse effect of singlet oxygen that is produced in the oxygen-sensitive beads. The sensor chemistry for DO/pH was modified.

Non-invasive, simultaneous optical monitoring of oxygen and pH during bacterial cultivation in 24-well microplates is presented using an integrated dual sensor for dissolved oxygen and pH values. The dual sensor is based on oxygen-sensitive organosilica microparticles and pH-sensitive microbeads from a polymethacrylate derivative embedded into a polyurethane hydrogel. The readout is based on a phase-domain fluorescence lifetime-based method referred to as modified frequency domain dual lifetime referencing using a commercially available detector system for 24-well microplates. The sensor was used for monitoring the growth of Pseudomonas putida bacterial cultures. The method is suitable for parallelized, miniaturized bioprocessing, and cell-based high-throughput screening applications.

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