Electrografting of thionine diazonium cation onto the graphene edges and decorating with Au nano-dendrites or glucose oxidase: Characterization and electrocatalytic applications

Thionine (Th) diazonium cation is covalently attached onto the glassy carbon (GC) electrode via graphene nanosheets (GNs) (GC-GNs-Th). The GC-GNs-Th electrode is subjected to further modifications to fabricate (i) glucose and (ii) nitrite sensors. Further modifications include: (i) direct immobilization of glucose oxidase (GOx) and (ii) electrodeposition of gold dendrite-like nanostructures (DGNs) on the GC-GNs-Th surface, constructing GC-GNs-Th-GOx and GC-GNs-Th-DGNs modified electrodes, respectively. The GC-GNs-Th-GOx biosensor exhibited a linear response range to glucose, from 0.5 to 6.0 mM, with a limit of detection (LOD) of 9.6 μM and high sensitivity of 43.2 µA cm−2 mM−1. Also, the GC-GNs-Th-DGNs sensor showed a wide dynamic response range for NO2- ion with two linear parts, from 0.05 μM to 1.0 μM and 30.0 μM to 1.0 mM, a sensitivity of 263.2 μA mM−1 and a LOD of 0.01 μM. Applicability of the modified electrodes was successfully tested by determination of glucose in human blood serum and nitrite in water based on addition/recovery tests.