Paper-Based All-Solid-State Ion-Sensing Platform with a Solid Contact Comprising Colloid-Imprinted Mesoporous Carbon and a Redox Buffer

We report the design, structure, and performance of a planar paper-based ion-sensing platform that utilizes colloid-imprinted mesoporous (CIM) carbon as a solid contact, with a redox buffer as the internal reference. This device contains an all-solid-state ion-selective electrode and an all-solid-state reference electrode that are integrated into the paper substrate with a symmetrical cell design. To ensure calibration-free sensor operation, each interfacial potential within the device is well-defined by the use of a redox buffer added to the sensing and reference membranes that controls the interfacial potentials at the CIM carbon/sensing membrane and CIM carbon/reference membrane interfaces. Two types of redox buffers were evaluated for this purpose, i.e., one based on the tetrakis(pentafluorophenyl)borate salts of cobalt(II/III) tris(4,4′-dinonyl-2,2′-bipyridyl) and one consisting of 7,7,8,8-tetracyanoquinodimethane and its corresponding anion radical. The feasibility of the design was demonstrated with aqueous KCl solutions. By design, the device only needs one droplet of sample, and it does not need any supply reagents or sensor pretreatment (i.e., conditioning and calibration) to function.