A polymeric junction membrane for solid-state reference electrodes

A polymer membrane system composed of 30 wt.% cellulose acetate (CA) and polyurethane (PU) has been developed for the fabrication of mass producible solid-state reference electrodes. The CA/PU membrane exhibits appropriate adhesion to common substrates (e.g., ceramic and silicon chips) of miniaturized electrochemical sensors, allows quick hydration of internal hydrogel layer (3 M KCl with a 6 wt.% water soluble polymer) deposited on micro-patterned electrodes resulting in fast preconditioning time (∼100 s), and provides a stable reference potential for an extended period (use-lifetime: 25-90 min) by limiting the diffusion of internal electrolytes. The potentiometric responses of the CA/PU membrane-based solid-state reference electrodes drifted rapidly (40-90 mV/h) after their use-lifetime; the results suggest that the internal electrolyte slowly fills the micro-channels of the outer membrane while maintaining stable potential, and begins to diffuse away at an increased rate from the membrane/aqueous solution interface. The potentiometric responses of the polymer membrane-based ion-selective electrodes (for Na+, K+, Ca2+, Cl− and H+) formed on the same chip with the CA/PU membrane-coated Ag/AgCl reference electrode were examined both in aqueous and physiological samples; their analytical performance closely matched that of sensors measured against a conventional reference electrode.