FLUORESCENCE OPTICAL UREA BIOSENSOR WITH AN AMMONIUM OPTRODE AS TRANSDUCER

An optical sensor for determination of urea is presented that is based on the measurement of the amount of ammonium ion produced through the enzymatic action of urease at physiological pH. The ammonium optrode sensor acting as the transducer consists of a PVC material containing an ammonium ion carrier and a proton carrier (a protonated dye) whose colour changes in accord with the ammonium concentration. An urea biosensor was obtained by coupling this ammonium transducer to the enzymatic hydrolysis of urea. The sensor fully reversibly responds to urea, with detection limits varying from 0.03 to 0.6 mM at near neutral pH. The response is highly pH-dependent, and response times are about 4 min for enzyme membrane thicknesses of ca. 150 mum.