UREA POTENTIOMETRIC BIOSENSOR BASED ON UREASE IMMOBILIZED ON CHITOSANMEMBRANES

Potentiometric biosensors based on urease (E.C. 3.5.1.5.) immobilized on chitosan membranes coupled to all-solid-state nonactin ammonium ion selective electrodes are described.:The enzyme was immobilized on the chitosan membranes by four procedures: (A) adsorption; (B) adsorption followed by reticulation with dilute aqueous glutaraldehyde solution; (C) activation with glutaraldehyde followed by contact with the enzym e solution; and (D) activation with glutaraldehyde, contact with the e nzyme solution and reduction of the Schiff base with sodium borohydrid e. The response characteristics of the biosensors obtained with these enzymatic membranes were determined and compared. The biosensor with b est response characteristics, obtained by procedure (B), showed the fo llowing characteristics of response to urea: (i) linearity in the 10(- 4) to 10(-2) M range; (ii) slope of up to 56 mV per decade; (iii) resp onse time between 30 s and 2 min; and (iv) lifetime of 2 months. This biosensor was tested in the determination of urea in blood serum sampl es. (C) 1998 Elsevier Science B.V. All rights reserved.