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 monitoring the concentration of a specific nonionic microsolute (glucose) in a multicomponent aqueous solution (e.g., whole blood or plasma) is described, and preliminary experimental evidence supporting the validity of the sensor concept is presented. Detection is based upon the use of a glucose-selective complexing agent (a boronic acid immobilized in a hydrogel) which liberates a mobile microion (hydrogen ion) when it binds a glucose molecule. The change in ionic conductivity of the hydrogel resulting from the increase in ion concentration is thus directly related to the ambient glucose concentration. Confinement of the liberated ions within the hydrogel, and prevention of entry of extraneous electrolytes present in the test solution, is necessary to make the conductimetric measurement meaningful. This is achieved by encapsulating the hydrogel within a bipolar ion exchange membrane impermeable to ions but freely permeable to glucose (and other nonionic microsolutes). A physicochemical model of the complexation equilibrium, kinetics of solute transport through the membrane and hydrogel phase, and their impact upon the ionic conductivity of the hydrogel is presented, which supports the utility of this sensor concept as a potentially reliable and sensitive glucose monitor. Its generic utility for monitoring nonionic microsolutes in multicomponent aqueous solutions is suggested.