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 voltarnmetric inlaid disk type gold microelectrode by chemical etching of the gold microwire. The microcavity of ca. 50 pL volume and 25 mu m diameter accommodates the inherently conducting polymeric inner contact and the ionselective 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.