Ratiometric Fluorescent Nanohybrid for Noninvasive and Visual Monitoring of Sweat Glucose

Noninvasive and visual monitoring of glucose is highly desirable for diabetes diagnostics and long-term home-based health management. Owing to the correlation of the glucose level between blood and sweat, on-body sweat glucose detection provides potential for noninvasive healthcare but is highly challenging. Herein, we for the first time demonstrate a wearable skin pad based on the ratiometric fluorescent nanohybrid, which can realize noninvasive and visual monitoring of sweat glucose. Luminescent porous silicon (PSi) particles, which have a porous structure and oxidation-responsive photoluminescence decay, are chosen to load (adsorb or entrap) carbon quantum dots (CQDs) for the construction of the dual fluorescence nanohybrid. Bimetallic (Au and Ag) nanoparticles (BiM) are also co-decorated on the PSi particle to improve detection sensitivity by enhancing PSi's initial fluorescence and oxidation kinetics. Owing to the efficient fluorescence resonance energy transfer effect, BiM-CQDs@PSi initially exhibits PSi's red fluorescence with complete quenching of CQDs's blue fluorescence. The oxidation of PSi triggered by hydrogen peroxide (H2O2) weakens the FRET effect and decays PSi's fluorescence, causing ratiometric fluorescence to change from red (PSi) to blue (CQDs). A wearable skin pad is easily fabricated by co-immobilization of BiM-CQDs@PSi and glucose oxidase (GOX) in a transparent and biocompatible chitosan film supported by an adhesive polyurethane membrane. When the skin pad is attached on the body, the same ratiometric fluorescence transition (red -> blue) is observed upon the stimulation of H2O2 generated in GOX-catalyzed oxidation of sweat glucose. Based on the strong correlation between the ratio of the fluorescence change and sweat glucose level, clinical tests toward diabetics and healthy volunteers can clearly indicate hyperglycemia.