Whispering gallery mode resonator and glucose oxidase based glucose biosensor

In this research whispering gallery mode resonators (WGMRs) were applied in new concept of glucose sensor based on the shift of WGM resonance frequency induced by enzymatic oxidation of glucose by glucose oxidase (GOx), which was immobilized on WGM-resonator surface. During the enzymatic reaction catalyzed by GOx electrons from glucose via GOx are transferred towards co-immobilized gold nanoparticles (Au-NPs). WGM-resonators were fabricated from standard telecommunication optical-fiber melted in a hydrogen flame. Whispering gallery mode resonance based optical signals generated by these WGM-resonators were evaluated. These WGM-resonators, which were characterized by sufficient quality factors, were modified with Au-NPs using dip coating method in order to form hybrid WGM-resonator (WGMRs/Au-NPs) structure. Then WGMRs/Au-NPs structure was investigated using SEM and, after these investigations, the sensitivity of WGMRs/Au-NPs-based resonators towards glucose has been assessed by the evaluation whispering gallery mode resonance based optical signals. Then the next modification step of WGMRs/Au-NPs resonators by enzyme – GOx – has been performed in order to design WGMRs/Au-NPs/GOx-based resonator structure, which showed increased sensitivity towards glucose in comparison to that of WGMRs/GOx-based resonators, which were not modified by Au-NPs. WGMRs/Au-NPs/GOx-based glucose sensor was tested at several glucose concentrations in the range up to 2.4 mM and it was determined that WGM-resonance frequency shift rate significantly increases at higher glucose concentrations. Therefore, WGM-resonance frequency shift rate was determined as characteristic of analytical signal suitable for the determination of glucose concentrations by sensors based on both WGMRs/GOx and WGMR/Au-NPs/GOx resonators.