Ion-selective conductometric microsensors based on the phenomenon of specific salt extraction

Abstract

Ion activity measurements in aqueous media are fundamental to an extremely wide range of problems from cell membrane transport studies to environmental monitoring and chemical oceanography. The use of potentiometric ion-selective electrodes (ISE) in these areas is now practically indispensable. During the 1970s and 1980s a number of approaches (e.g. ion-selective field-effect transistors [1], coated-wire electrodes [2]) were proposed in order to miniaturise the ion-selective sensors, simplify their fabrication and extend the scope of their application. However, this drive for miniaturisation and integration was not fully accomplished, since the technical solution that would allow the fabrication of a solid-state, group-technology-compatible reference electrode is not yet available, so single probe all-solid-state potentiometric ion microsensors still cannot be produced [3]. In fact, the taste of design and fabrication of the miniaturised, integrated reference electrode is recognised as one of the central challenges in the field of integrated chemical sensors [3,4]. As alternatives to potentiometric measurements of the ion activities one may mention different optical ion sensors, in particular, ion-carrier-based optodes [5], measurements of the conductivity of pH-sensitive swelling gels [6], and monitoring of the resistance of the interface ion-sensitive membrane Isolution ([7,8] and references cited therein). We report here proof-of-concept results demonstrating a new approach to electrochemical ion sensors: ion-selective ~nductometric Q!icrosensors (ISCOM). Det~ctio~ is accomplished by measurement of the bulk conductance G B of a thin plasticised polymeric membrane containing an ionophore, where the magnitude of G B can be related to the contents of the primary ion in the analysed solution.