Nitrogen doped graphene and its derivatives as sensors and efficient direct electron transfer platform for enzyme biosensors

The performance of different sensor/biosensor architectures based on graphene (G), nitrogen doped graphene (NG) and their acidic/basic functionalized derivatives, as well as of polymer composites of NG have been compared, using ascorbate oxidation, and glucose enzymatic oxidation, as model reactions on glassy carbon electrode (GCE) substrates, which led to the choice of NG/GCE as the preferred modified electrode for further applications. Enzymatic and non-enzymatic sensing of hypoxanthine (Hx) and xanthine (X), two intermediates in purine metabolism, with relevance in clinical diagnostics and food chemistry, was investigated. Electrocatalytic oxidation of both Hx and X was achieved at NG/GCE, the sensor exhibiting sensitivities of 1.6 and 1.3 mA cm−2 mM−1 for Hx and X, respectively. Hx biosensing was carried out at −0.35 V vs. Ag/AgCl, the enzymatic mechanism being based on direct regeneration of FAD at NG, the analytical characteristics comparing favorably with other reported XOx biosensors. Application to the analysis of biological samples was demonstrated.