Development of carbon nanomaterial and mediator-based amperometric biosensor for the determination of xanthine

In this thesis, an electrode modified with carbon nanofiber (CNF) and ferrocene carboxylic acid (Fc-COOH) was prepared. An amperometric biosensor was prepared for xanthine determination by immobilizing xanthine oxidase (XO) enzyme on this modified glassy carbon electrode (GCE) surface using cross-linking method. Scanning electron microscopy method was used to characterize the surface morphology of the biosensor. The optimum surface composition of the enzyme electrode, operating conditions, performance factors and applicability to the determination of xanthine in real samples were investigated. The optimal amount of mediator and enzyme, working potential and buffer pH for the developed XO/Fc-COOH/CNF/GCE were found to be 5 µL, 3 U, +0.40 V and pH 8.0, respectively. The linear working range of the biosensor was 6,010-7  2,010-4 M, sensitivity was 4,48 µA µM-1, detection limit was 1.7×10-7 M and response time was 11 s. In the reproducibility and repeatability studies, the relative standard deviation was calculated as 3.0% and 3.6%, respectively. The effect of the species found in real samples that can cause interference on the biosensor response was investigated. It was seen that xanthine determination in fish can be performed successfully with the prepared biosensor.