Evaluation and Adaptation of an Ion Sensitive Field Effect Transistor for Seawater pH Applications

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pH is of fundamental importance to contemporary issues in chemical oceanography such as ocean acidification and biogeochemical cycling, yet continues to be chronically undersampled in both space and time. This problem can only be overcome through the development of sensors capable of stable, long-term autonomous operation in situ. The approaching age of ocean observatories desperately needs such sensors for the various types of proposed platforms (e.g. moorings, profiling floats, gliders). The PI?s propose to evaluate the performance of the ion sensitive field effect transistor (ISFET) for measuring seawater pH. Initial tests at MBARI indicate that commercial ISFETs may now be capable of long-term operation in the surface ocean with minimal sensor drift. A side-by-side assessment of commercially available ISFETs will be carried out at MBARI. Off-the-shelf ISFETs will also be deployed on ocean moorings to test the effects of biofouling and to determine the necessary anti-biofouling measures. Concurrent to this, MBARI will work with existing chip technologies to build an ISFET sensor specifically intended for seawater pH measurements. In designing the customized ISFET, special attention will be given to pressure tolerance and type of reference electrode. Broader Impacts: pH value is among the most critical chemical parameters to our study in oceanography. At present time, there is no any other progress as successful as PI's work in obtaining long term pH measurement in seawater. Benefit of this development is almost no limitation to entire ocean science community. The improved ISFET pH sensor technology from this effort will certainly be valuable to our development towards other chemical sensors for gaining long term monitoring ability. In addition, the experience and knowledge gained through this sensor related development will also benefit wide ranges of the engineering community in dealing with long term monitoring of chemistry in aqueous system. Its hard to name anything more important than the carbon cycle in the ocean right now, and this sensor would be a great help in understanding its spatial and temporal variability. A successful sensor would have wide application in ocean observing system and in all sorts of autonomous vehicles as well as ship-based field programs. Their WATCH program will involve under-represented groups in the data analysis.