Sung Dong Lee

Solid-state ion sensors with a liquid junction-free polymer membrane-based reference electrode for blood analysis

Abstract A set of ion-selective membranes for the measurement of clinically relevant electrolytes, i.e., K+, Na+, Ca2+, H+ and Cl−, and a solvent-processible polyurethane (PU)-based reference membrane were cast on metal electrodes patterned on small ceramic plates, and on silicon-based sensors. Since the liquid junction-free PU membrane-based reference electrode provides a constant potentiometric signal for an extended period of time, accurate determination of blood electrolytes could be made without using a separate reference flow. The PU membrane-based reference electrodes not only improve the mass producibility of miniaturized solid-state ion sensors but also simplify the configuration of flow cell cartridges without compromising their analytical performance.

Potentiometric biosensors using immobilized enzyme layers mixed with hydrophilic polyurethane

Abstract Potentiometric biosensors using asymmetric type polyurethane (PU) membranes are reported. The proposed membrane system consists of a thin hydrophilic polyurethane (HPU) film directly mixed with an enzyme that is coated over an underlying plasticized PU-based ion-selective membrane. It is shown that the intrinsic potentiometric response of the basic ion-selective PU membrane is not influenced significantly by the HPU/enzyme film coated on its sensing surface. Since the PU-matrix membrane adheres tightly to the solid surface and there is no need for an additional chemical reaction step such as glutaraldehyde crosslinking to attach enzymes to the membrane surface, the PU/HPU/enzyme membrane system is well suited for fabrication of solid-state type potentiometric biosensors. As examples, urease, adenosine deaminase and glucose oxidase are immobilized on ammonium- or proton-selective membranes to fabricate urea, adenosine and glucose sensors.

Amperometric biosensors employing an insoluble oxidant as an interference-removing agent

Abstract A strong oxidant membrane is introduced to amperometric biosensors in order to solve the problem associated with interference from readily oxidizable species. The proposed biosensors are in planar format, and are composed of four components, i.e. a base amperometric transducer, an enzyme layer, a protecting membrane, and an oxidant membrane. In this sensor format, interfering species are removed by an oxidation reaction during their diffusion through the oxidant membrane. The oxidant membrane is introduced by dispensing a mixture of an oxidant and a polymer matrix as dissolved in an organic solvent, and thus, could be easily adapted to mass fabrication of miniature biosensors. In this work, several different reagents are examined as oxidants: BaO2, CeO2, MnO2 and PbO2. Of these, PbO2 is shown to yield biosensors with the best performance, in terms of reducing interfering signals. Two different matrix systems are devised for use in formulating oxidant membranes: hydrophilic polyurethane (HPU) and cellulose acetate incorporating poly(ethylene glycol) (CA/PEG). While the CA/PEG-type sensor displays better sensitivity and faster response behavior, the HPU-type is shown to exhibit more pronounced interference-removing ability. The analytical utility of the proposed oxidant membrane is demonstrated by fabricating amperometric glucose and creatinine sensors as the model biosensor systems, and by investigating their response characteristics.