Amperometric biosensors based on carboxylated multiwalled carbon nanotubes-metal oxide nanoparticles-7,7,8,8-tetracyanoquinodimethane composite for the determination of xanthine

A comparison of the analytical performances of two xanthine biosensors, based on the use of different metal oxide nanoparticles (MONPs: Co3O4 or Fe3O4)-modified carboxylated multiwalled carbon nanotubes (c-MWCNTs)-7,7',8,8'-tetracyanoquinodimethane (TCNQ)-chitosan (CHIT) composite, is discussed. Xanthine oxidase (XOD) enzyme was covalently attached to c-MWCNTs/MONP5/TCNQ/CHIT/GCE via N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry and the electrode surface was further modified with Nafion in order to minimize the effect of possible interfering substances. The results showed that analytical performance of the Fe3O4 based biosensor was better than the Co3O4 based biosensor. The linear working range, limit of detection and sensitivity were found to be 1.9x10(-6)-2.3x10(-4) M, 0.20 mu M (S/N=3), 25.07 mu Am M-1 cm(-2) for the Fe3O4 based biosensor and 1.9x10(-6)-1.2x10(-4) M, 0.36 mu M (S/N=3), 13.24 mu Am M-1 cm(-2) for the Co3O4 based biosensor, respectively. The purposed biosensors were applied in the determination of xanthine in coffee samples, and satisfactory results were obtained.