Superparamagnetic Fe3O4 nanoparticles were coated with (3-aminopropyl)triethoxysilane and further branched with monomethoxypolyethylene glycol chains. These nanoparticles were employed for the non-covalent surface modification of single walled carbon nanotubes, conferring them magnetic properties. This nanomaterial was employed to immobilize the enzyme xanthine oxidase in order to construct magnetically modified disposable gold screen-printed electrodes as bioelectrodes for the determination of xanthine. The electroanalytical properties of the biosensor were modulated by the nanomaterial composition, being optimal at a carbon nanotubes : magnetic nanoparticles ratio of 1 : 27. The resulting biosensor showed a linear dependence on the xanthine concentration in the 0.25–3.5 μM range with a fast amperometric response in 12 s. The biosensor also showed a noticeable high sensitivity of 1.31 A M−1 cm−2 and a very low detection limit of 60 nM, which can be compared advantageously with other biosensor designs for xanthine.
