MINIATURIZED THIN-FILM CONDUCTOMETRIC BIOSENSORS WITH HIGH DYNAMIC-RANGE AND HIGH-SENSITIVITY

Conductometric measurements are of interest in analytical chemistry. T hey provide an overall-sight of the ionic strength in electrolytes and can be used for analytical purposes if they are provided with a selec tivity factor, e.g. enzyme membranes. Miniaturised transducers were fo rmed by means of photolithography, thin film, and plasma technologies. Two-and 4-electrode measurements were taken to characterise sensitivi ty and dynamic range. However, using 4-electrode measurements expands the dynamic range from deionised water up to 1 mol KCl-solution and in creases the sensitivity at high background conductivity. Such measurem ents were taken out with electrodes which had an interdigital distance of 50 mu m and an area of 0.04 mm(2). Additionally, interdigital stru ctures with interdigital distances of 5 mu m were investigated. Coated with a poly-HEMA membrane wherein urease was immobilised, a urea sens or was constructed. The concentration-range of urea was 1-30 mmol urea in 20 mmol HEPES-buffer. (C) 1997 Elsevier Science S.A.