Abstract:

Diabetes Mellitus is one of the rising chronic diseases of our time. The need for non- invasive glucose sensors compatible with the continuous monitoring of glucose levels and thus close monitoring of Diabetes Mellitus is difficult to fulfill. This thesis aims to investigate a specific approach that could result in non-invasive glucose sensing in the long term. We do so by designing, constructing, and characterizing an optical detection system to perform non-invasive spectroscopy of tissue. The system employs a quantum cascade laser as a mid-infrared excitation source, respon- sible for inducing a thermal change in the specimen under investigation. This thermal change varies the thermal radiation emitted by the specimen that an infrared sensor subsequently detects. The temperature increase experienced by the sample is due to the radiationless relaxation of the previously excited vibrational states, which are unique to each specimen and thus offer the possibility to identify molecules with high specificity. The system’s performance is tested on several phantoms. All results report high signal-to- noise (SNR), with the signals of interest being three to four orders of magnitude larger than the dark noise. The spectra show robustness against external and internal factors, with deviations from the mean of less than 2%, a value sufficiently low for the pursued application. Furthermore, the acquisition of spectra at the fastest scanning speed available is demonstrated. Another feature that we evaluate is the linearity of the signal’s amplitude with the analyte’s concentration. The preliminary study of the method’s linearity is promising, but further tests are necessary for a solid validation of the implemented system as a spectrometer.