Non-invasive Glucose Monitoring: Miniaturization of an in vivo Glucose Sensor Based on Mid-Infrared Laser Spectroscopy

Abstract

Non-invasive glucose sensing is a desirable technology that has the potential to improve the quality of life for millions of people affected by diabetes worldwide. It has been previously demonstrated that in vivo glucose detection in the interstitial fluid is possible by collecting backscattered light emitted by a quantum cascade laser (QCL). To date, this technique has made use of a tunable QCL, a thermo-electrically cooled MCT detector, and an integrating sphere made of a gold-plated diffuse scattering surface to collect highly angle-dependent scattering patterns of light. However, this system is made from standardized and rather large individual components that, while functional, do not produce the desired portability of a marketable sensor. Through careful consideration, it has become apparent that this sensor’s optical components are particularly important to the sensor’s functionality both in terms of accuracy and in reference to size and usability. Hence, this thesis primarily investigates, through modelling and experimentation, a shift in optical components from an integrating sphere to a set of miniature optical lenses including a compound lens composed of a Germanium prism and ZnSe hemisphere. Through methodical simulations conducted in Zemax software, it has been demonstrated that a lens-based optical system has the potential to produce an efficiency of approximately 30% in comparison to the 24% produced by the previous sphere apparatus, indicating that such a system can significantly increase device portability while maintaining accurate performance. The new light collection device is also 150 times smaller than the previous device. Furthermore, corresponding design considerations are made to experimentally fabricate and test the device in the lab. Such considerations include QCL fabrication and placement, device housing, and data processing. Hence, the presented design demonstrates the potential for a wearable non-invasive glucose sensor.