Robust Dual Optical Sensor for pH and Dissolved Oxygen

As part of moving our optical pH and dissolvedoxygen (DO) optical chemosensors toward industrial applications,we decided to explore a many-sensors-in-one principle. It wastested if physical segregation of the optical sensor components in asingle sensor polymer could remove cross-talk and quenching. Itwas found that a design concept with an oxygen-responsive dye inpolymer nanoparticles and a pH-responsive dye in an organicallymodified siloxane polymer resulted in a robust pH/O2dual opticalsensor. Individually, the O2-sensitive nanoparticles, a knowncomponent for optical DO sensing, and the pH sensor areoperational. Thus, it was decided to test if nanoparticles enclosedwithin the pH-sensitive responsive sol-gel (i) could work togetherif segregated and (ii) could operate with a single intensity signalthat is without a reference signal; developments within industrial optical sensor technology indicate that this should be feasible. Theprototype optode produced in this work was shown to have a negligible drift over 60 h, bulk diffusion-limited DO response, andindependent response to pH and O2. On the individual optode, pH calibration was found to show the expected sigmoidal shape andpKa, while the complexity of the calibration function for the DO signal was significant. While the engineering of the sensor device,optics, and hardware are not robust enough to attempt generic sensor calibration, it was decided to demonstrate the design conceptin simple fermentation experiments. We conclude that the dual sensor design with the physical segregation of components is viable.