A contact lens like material is coated with metamaterial structures (gold nanostructures with a single resonance in the near-infrared), so that the lens can be inserted directly into the patient’s eye. The metamaterial on top of the contact lens reflects an infrared laser beam and the reflected as well as the transmitted beam are measured by photodiodes in an experimental setup. The detected transmission and reflection spectra show characteristic maxima and minima, which react highly sensitive to changes (e.g. of the refractive index of the sample) and change their resonance. In order to only detect changes in specific substances (glucose in this case), a glucose sensitive hydrogel is coated on top of the metamaterial (see figure 1). When glucose is diffusing into the hydrogel, the hydrogel absorbs water and starts to swell. The degree of the swelling is thereby dependent on the glucose concentration of the surrounding tear liquid, which changes the refractive index of the sample. These changes can be observed in the spectral measurement data.
Figure 1: Set-up and functional principle of the contact lens.
By implementing an integrated data processing approach, the glucose concentration of the tear fluid can be estimated (see figure 2). The measurement data is evaluated and conditioned in order to determine the glucose concentration of the tear fluid by an inverse model.
Figure 2: Glucose concentration estimation of tear fluid via analysis of spectral measurement data and application of an inverse model.
- “Refractive Index Estimation from Spectral Measurements of a Plasmonic Glucose Sensor and Wavelength Selection”, IFAC World Congress, Toulouse, France, 2017 ,
- T. Teutsch, M. Mesch, H. Giessen & C. Tarín, “Discrete wavelength selection for the optical readout of a metamaterial biosensing system for glucose concentration estimation via a support vector regression model”, International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Milano, Italy, 2015, pp. 6421-6424, doi:10.1109/EMBC.2015.7319862
- T. Teutsch, M. Mesch, H. Giessen & C. Tarín, “Dynamic modeling of the hydrogel molecular filter in a metamaterial biosensing system for glucose concentration estimation”, International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Chicago, IL, USA, 2014, pp. 2081-2084, doi:10.1109/EMBC.2014.6944026