August 21, 2017
A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity (AT) using ion sensitive field effect transistor (ISFET) technology to provide a simplified means of characterization of the aqueous carbon dioxide system through measurement of two “master variables”: pH and AT. ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanographic applications. A modified ISFET is demonstrated to perform a nL-scale acid-base titration of AT in under 40 s. This method of measuring AT, a Coulometric Diffusion Titration, involves electrolytic generation of titrant, H+, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e. OH–, HCO3–, CO32-, B(OH)4–, PO43-) of seawater AT. The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in AT over the range of seawater AT of ~2200-2500 μmol kg-1 which demonstrates great potential for autonomous sensing.
Link to article: http://pubs.acs.org/doi/abs/10.1021/acssensors.7b00305