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Simple method of enzyme immobilization for pH-ISFET-based urea biosensors

In this paper, a simple chemical method of urease immobilization on silicon nitride surface is described. As a basic structure to construct urea-biosensor, a pH-sensitive Si3N4-gate ISFET was used. The developed method of chemical immobilization of urease is based on Schiff's base formation. The developed EnFET type urea biosensor are characterized by the following parameters: (1) maximum analytical signal: 120 divided by 140 mV in 10 mM phosphate buffer solution, (2) linear range of the (Delta) Ugs equals f(logCurea): pCurea(2 divided by 3.5) in 10 mM phosphate buffer, (3) response time: 80 s and (4) lifetime: 35 days with the stable analytical signal then after 52 days this signal decreased by at least 40%. The influence of the concentration as well as the pH of the buffer solution on EnFET response were investigated.