Online electrochemical method for continuous and simultaneous monitoring of glucose and l-lactate in vivo with graphene hybrids as the electrocatalyst

This study described a physiologically relevant on-line electrochemical method for simultaneous monitoring of glucose and l-lactate in vivo with good sensitivity and selectivity. The analytical system that constructed by dual-enzyme biosensor was based on a novel and effective graphene hybrids with the on-line microdialysis system, which made the continuous and simultaneous monitoring of striatum glucose and l-lactate in brain of freely moving rats possible. The dual-enzyme biosensor was accomplished by using oxidases as the specific sensing unit and the UV-assisted synthesized Graphene/ZnO@Pd as the electrocatalyst. Transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray and X-ray photoelectron spectroscopy confirmed the denoted Pd nanoparticles (NPs) on the Graphene/ZnO composites. The analytical system showed good linearity for glucose and l-lactate concentrations from 20 μM to 500 μM with detection limit of 2.39 μM and 2.52 μM respectively. After post-calibration, the basal level concentrations of glucose and l-lactate in the microdialysate from the striatum of freely moving rats were calculated to be 0.323 ± 0.021 mM and 0.501 mM ± 0.057 mM (mean ± s.d., n = 3). Moreover, the dual oxidase/Graphene/ZnO@Pd based biosensors suffered from little cross-talk and exhibit a good stability and reproducibility.