The detection of the ammonium ion produced by the enzymatic action of
urease on urea is investigated electrochemically by means of facilitat
ed ion transfer reactions at liquid-liquid micro-interfaces. The ureas
e was used either in a dissolved form (free in aqueous solution) or im
mobilized onto the surface of an ammonia gas permeable membrane. The s
ensing structure utilizing the ammonia gas permeable membrane allowed
the detection of urea from 200 mu M to 4mM. Thick film technology was
utilized in conjunction with UV excimer laser photoablation techniques
to fabricate a microelectrode strip sensor for the ammonium ion.