Prussian Blue Analogues: A Versatile Framework for Solid-Contact Ion-Selective Electrodes with Tunable Potentials

The development of solid-contact ion-selective electrodes (SC-ISEs) (e.g. for point-of-care sensors) requires simple inner reference electrodes (iREs) with predictable and reproducible potentials. Intercalation compounds fulfill these requirements, as they respond to target ions present in the ion-selective membrane. Their applicability, however, is limited by the availability of intercalation frameworks capable to intercalate the target ion of interest. We report that Prussian Blue analogues (PBAs) can serve as versatile iREs for a range of target ions of clinical interest, such as Na+, K+, or Ca2+. Combining target-ion intercalated PBAs with ion-selective membranes results in a family of all-solid SC-ISEs, which are capable as ISEs with an inner filling, yet cheap and suitable for mass-production. The SC-ISEs standard potential is predictable and can be tuned by altering the PBAs redox-active transition metal or by changing its state of charge.