Microcavity Based Solid‐Contact Ion‐Selective Microelectrodes

A novel design and fabrication procedure is proposed for the preparation of robust ionophore based ion‐selective microelectrodes. The essential component of the new design is a microcavity that is formed after recessing a voltammetric inlaid disk type gold microelectrode by chemical etching of the gold microwire. The microcavity of ca. 50 pL volume and 25 μm diameter accommodates the inherently conducting polymeric inner contact and the ion‐selective liquid membrane, which are thereby mechanically protected from the sample environment. As inner contacts poly(3,4‐ethylenedioxythiophene) (PEDOT) films doped with poly(4‐styrenesulfonate) (PSS) and tetrakis[3,5‐bis‐(trifluoromethyl)phenyl]borate (TFPB) electropolymerized from aqueous and organic solvents, respectively, were used. Potassium‐ and calcium‐selective microelectrodes fabricated according to the new procedure exhibited potentiometric characteristics similar to the conventional electrodes. The formation of an aqueous layer below the ion‐selective membrane could be avoided by using the proposed electrode construction.