Microfluidic Sweat Patch Integrated Smartwatch for Non-Invasive Photonic Continuous Glucose Monitoring

Managing diabetes is a chronic challenge and requires continuous glucose monitoring (CGM) for timely insulin delivery to maintain the homeostasis of blood glucose levels. Instead of blood sampling, CGM is based on the glucose monitoring in the body fluids such as sweat, tear, saliva, interstitial fluid, and so on. Wearable sweat sensor is a promising approach for CGM, but there are several challenges including stable sweat collection and sustainable reusability of glucose sensors. Here, we present a photonic sweat glucose patch sensor incorporating a Tesla valve-based microfluidic system designed for continuous sweat flow without evaporation. The Tesla valve microfluidic structure promoted unidirectional flow with minimal backflow, improving sweat acquisition efficiency. The performance of Tesla valve was validated by flow experiments with methylene blue and methyl red indicators. Glucose sensing was achieved by using glucose-responsive hydrogels immobilized in a microfluidic reservoir containing an oxygen-sensitive phosphorescent dye and glucose oxidase. The green LED of a smartwatch was used to sequentially excite the sensing hydrogel and the fluorescence intensity change was measured by a photodetector to monitor glucose levels. In vitro tests confirmed the successful monitoring of glucose levels ranging from 0.01 mM to 1 mM. Additionally, human trials showed the strong correlation between sweat and blood glucose levels before and after meals. Taken together, we could confirm the feasibility of microfluidic sweat patch integrated smartwatch for photonic CGM applications.