[C₃(OH)₂mim][BF₄]-Au/Pt biosensor for glutamate sensing in vivo integrated with on-line microdialysis system

A new type of hydroxyl functionalized room temperature ionic liquid (RTIL), [C₃(OH)₂mim][BF₄], was synthesized herein and a novel H₂O₂ biosensor is fabricated with [C₃(OH)₂mim][BF₄] as the substrate and electrodepositing bimetallic Au/Pt nanoparticles (NPs) onto the [C₃(OH)₂mim][BF₄] film. The functionalization of RTIL with hydroxyl groups provided an appropriate environment for the preparation of more uniform and smaller Au/Pt NPs with the diameter of 2.5nm±0.2nm. Immobilized with glutamate oxidase (GlutaOx), the resulting GlutaOx-[C₃(OH)₂mim][BF₄]-Au/Pt-Nafion biosensor displayed excellent electrocatalytic response to glutamate at a potential of -200mV. An effective on-line microdialysis system, which was powered by a microdialysis pump, was set up and used for the detection of glutamate successively in the striatum of rats. The glutamate biosensor in on-line microdialysis system showed good linear range from 0.5μM to 20.0μM with the detection limit of 0.17μM (S/N=3). The basal level of glutamate in the striatum of anaesthetic rats was calculated to be 3.01±0.67μM (n=3). The application of the GlutaOx-[C₃(OH)₂mim][BF₄]-Au/Pt-Nafion electrode is further demonstrated for in vivo sensing of the variation of glutamate level in the striatum when rats received intraperitoneal (i.p.) injection of 100mM KCl and brain electrical stimulation of the subthalamic nucleus area (STN). Both of the two kinds of stimulation resulted in an increase in the extracellular concentration of glutamate. This method has proved to be sensitive and reproducible, which enables its promising application in physiology and pathology.