Noninvasive optical glucose monitoring at physiological levels using a functionalized plasmonic sensor

Summary form only given. Optical glucose sensing is crucial for noninvasive diabetes monitoring. One possibility is to analyze the tear liquid in the eye. We utilize complex plasmonic nanostructures and the slopes of their resonance structures in combination with a hydrogel layer that was functionalized with aminophenylboronic acid to selectively detect glucose in an aqueous solution at the millimolar level, which represents physiological concentrations in the blood as well as in the tear liquid. We observe spectral shifts in the range of a few nanometers that are linear for not too high concentrations due to local refractive index variation at the near fields of the gold nanostructures.The transmittance curves show good enough reproducibility and low spectral shift variation upon repeated experiments, which can be easily compensated using data processing techniques. We also demonstrate that our structure does not show hysteresis upon exposure and withdrawal of glucose even at levels of 50 mM. We integrated the functionalized nanostructure into a demonstrator that was able to record and display the glucose level on a tablet computer in real time. Our sensor concept could be utilized on a soft contact lens that could be worn for a few days, read out either by a laser/photodiode combination in reflection, in particular as we work at eye-safe wavelengths around 1.5 μm.