A Graphenic Biosensor for Real-Time Monitoring of Urea During Dialysis

A patient at the fifth stage of chronic kidney disease usually needs dialysis or transplantation. The adequacy of dialysis can be assessed by the dimensionless parameter Kt/V, which depends on the concentration of urea in the blood. Kt/V is usually measured before and after treatment, or by an indirect measurement of dialysis fluid conductivity. For the real-time monitoring of the urea concentration during dialysis, this paper proposes a disposable biosensor that combines a pH sensitive reduced graphene oxide layer functionalized with 4-amino benzoic acid and urease. Urease is immobilized on reduced graphene oxide and catalyzes the hydrolysis of urea into carbon dioxide and ammonia. This catalysis increases the pH value locally and elicits a sensor response. Urea concentration was assessed in the plasma of five dialyzed patients using a potentiometric measurement. The response time was 120 s and the error was 6 +/- 3% compared with standard clinical laboratory analysis.