Surface area independent response of closed bipolar electrodes

Here, we demonstrated the application of a closed bipolar electrode to measure the change in open circuit potential (OCP) of Prussian blue/white as a function of [Cl⁻] concentration independently of electrode surface area. In this bipolar scheme, a potentiostat holds a constant voltage across two separate cells linked by a shared electrode that is sensitive to [Cl⁻] on one end and electrodeposited by Prussian blue on the other. As [Cl⁻] is added to the sample compartment, the ion associates with Ag⁺ to produce Ag/AgCl, altering the junction potential. This change is balanced electrochemically by a shift in the ratio of Prussian blue/Prussian white. A second potentiostat is used to monitor these changes over the Prussian blue electrode, yielding a for the quantification of chloride. We measured a range of 1.0 mM – 55 mM [Cl⁻] over various electrode surface areas, demonstrating that the signal response is independent of electrode area. Additionally, the system had the capability to translate signal across a single bipolar electrode while using differently sized electrodes in each compartment, a property that could be beneficial for microarrays or signal amplification.