A glucose-responsive microgel-based soft etalon as an epidermal glucose colorimetric sensor

Abstract

Colorimetric sensors are promising candidates for convenient monitoring of changes in glucose concentration via a wearable platform. Here, poly(N-isopropylacrylamide) (pNIPAm) microgels are used as a glucose-responsive layer in a soft Fabry-Pérot etalon structure, which is incorporated in a sensing chamber for colorimetric on-body measurements. The sensing mechanism is based on dimensional changes of pNIPAm microgels in response to changes in glucose concentration, which cause spectral shifts of the reflected light in etalons. Using feed-type microgels for glucose-responsive etalon, we successfully observe distinguishable redshifts in the visible spectrum for the sweat glucose concentration of diabetic patients (0.01 ∼ 1 mM). Additionally, we introduce grid-shaped slits within the etalon structure to improve reaction time. The etalon sensor is also fabricated on a flexible substrate and is integrated into a soft sensing chamber to maintain high sensitivity during on-body measurement. The proposed non-invasive colorimetric sensor based on soft etalon suggests the possibility of simple on-body glucose measurements.