Layer-by-layer self-assembly of functionalized graphene nanoplates for glucose sensing in vivo integrated with on-line microdialysis system

In this work, a novel amperometric biosensor for hydrogen peroxide was fabricated through the layer-by-layer (LBL) self-assembling of amine-terminated ionic liquid (IL-NH ₂), and sulfonic acid (SO ₃ ^-) functionalized graphene by covalent bonding. The modification of the two functionalities introduced positive and negative charge onto the surface of graphene respectively, thus facilitating the formation of a multilayer film denoted with {IL-RGO/S-RGO} _n through electrostatic interaction and further immobilization of glucose oxidase (GOx). The resulting {IL-RGO/S-RGO} _n/GOx/Nafion biosensor displayed an excellent response to glucose at a potential of -200mV. Combined with on-line microdialysis system, the glucose biosensor in the on-line system showed good linear range from 10μM to 500μM with the detection limit of 3.33μM (S/N=3). Consequently, the basal level of glucose in the striatum of anesthetic rats was calculated to be 0.376±0.028mM (mean±s.d., n=3). The {IL-RGO/S-RGO} _n/GOx/Nafion biosensor was further applied for in vivo sensing of the glucose level in the striatum when rats received intraperitoneal (i.p.) injection of 30μL insulin, which resulted in an obvious decrease in the extracellular concentration of glucose within 30min. The method was proved to be sensitive and reproducible, which enabled its promising application in physiology and pathology.