A generic design of a flow-through potentiometric sensor array

In this paper, a flow-through potentiometric microsensor is described which is based on semipermeable tubing. The ion selective electrodes proposed ar e of the liquid membrane type in which a dialysis tube captures the ion sel ective cocktail. Ion selective sensors and a reference electrode based on t he same design were constructed by guiding a 0.3 mm diameter dialysis tube through a cavity precision machined in Perspex(R). Commercially available i onophore or ion-exchanger cocktails were applied to provide ion selectivity whilst a saturated KCl solution was used in the reference electrode. A num ber of flow-through microsensors selective to different ions (Na, K, Li, pH ) were constructed and tested. Each showed good performance in a broad rang e of concentrations. Advantages of the proposed approach are the generic te chnology to make sensors with incorporated reference electrodes, capable of measuring a wide variety of analytes for which cocktails are readily avail able and the fact that sub-microliter amounts of sample can be measured. Se condly, in comparison to other sensors applied in microchannels, the impeda nce of the flow-through sensor is much smaller because of the relatively la rge sensing surface formed by the tube wall. Moreover, the use of dialysis tubing enables easy integration with a so-called microdialysis probe for in -vivo sampling of the blood stream or subcutaneous tissue.