11] Hybrid biosensors for clinical analysis and fermentation control

Abstract

Publisher Summary A microbial sensor consisting of immobilized nitrifying bacteria and an oxygen electrode is used for the amperometric determination of ammonia. This chapter describes hybrid sensors for the amperometric determination of urea and creatinine. They are based on amalgamation of enzyme reactions and bacterial metabolism. Creatinine deiminase hydrolyzes creatinine to N-methylhydantoin and ammonium ion, and the ammonia produced is successively oxidized to nitrite and nitrate by nitrifying bacteria, which is already used in an ammonia sensor. The bacteria have not been completely characterized but are known to be a mixed culture of Nitrosomonas sp. and Nitrobacter sp. The reacting bacteria consume oxygen, so that the oxygen decrease may be detected by an oxygen electrode. The hybrid creatinine sensor thus consists of a cellulose dialysis membrane, immobilized creatinine deiminase, immobilized nitrifying bacteria, and an oxygen electrode. Urease hydrolyzes urea to ammonium ion and carbon dioxide. The improved ammonium ion sensor is developed and applied to the determination of ammonium ion. A urea sensor therefore consists of immobilized urease and an ammonium ion sensor. The chapter concludes that the use of hybrid biosensors appears to be quite promising for the amperometric determination of creatinine and urea.