A membrane-moderated, conductimetric sensor for the detection and measurement of specific organic solutes in aqueous solutions

A novel conductimetric sensor, capable of detecting and continuously monito ring the concentration of a specific nonionic microsolute (glucose) in a mu lticomponent aqueous solution (e.g., whole blood or plasma) is described, a nd preliminary experimental evidence supporting the validity of the sensor concept is presented. Detection is based upon the use of a glucose-selectiv e complexing agent (a boronic acid immobilized in a hydrogel) which liberat es a mobile microion (hydrogen ion) when it binds a glucose molecule. The c hange in ionic conductivity of the hydrogel resulting from the increase in ion concentration is thus directly related to the ambient glucose concentra tion. Confinement of the liberated ions within the hydrogel, and prevention of entry of extraneous electrolytes present in the test solution, is neces sary to make the conductimetric measurement meaningful. This is achieved by encapsulating the hydrogel within a bipolar ion exchange membrane impermea ble to ions but freely permeable to glucose land other nonionic microsolute s). A physicochemical model of the complexation equilibrium, kinetics of so lute transport through the membrane and hydrogel phase, and their impact up on the ionic conductivity of the hydrogel is presented, which supports the utility of this sensor concept as a potentially reliable and sensitive gluc ose monitor. Its generic utility for monitoring nonionic microsolutes in mu lticomponent aqueous solutions is suggested. (C) 2000 Elsevier Science B.V. All rights reserved.