One-Dimensional Responsive Photonic Crystals Assembled by Polymer Nanogels and TiO₂ Nanoparticles for Rapid Detection of Glucose

Diabetes, characterized by chronic hyperglycemia, has become a major threat to human health. A noninvasive, continuous, and rapid visual detection of glucose is still a challenge in application. In this study, one-dimensional photonic crystals (1DPCs) prepared via layer-by-layer assembling of glucose-responsive poly-(acrylamide-N,N'-methylenebis-(acrylamide)-3-acrylamide phenylboronic acid) (P-(AM-MBA-AAPBA)) nanogels and TiO2 nanoparticles are first confirmed for rapid and continuous colorimetric detection of glucose in physiological conditions. A two-step swelling mechanism of PCs was designed to speed up glucose diffusion and recognition. In detection, the PC sensor with a thickness of about 200 nm can rapidly imbue the polymer layer with water, causing the polymer layer to swiftly swell and create a pathway for mass transfer. Then, glucose molecules permeate in PC's channels and bind to phenylboronic acid (PBA) sites, prompting secondary expansion. Due to the inherent hydrophilicity of the polymer and the nanoporous structure of the TiO2 layer, PC sensors exhibit exceptional responsiveness, reaching sensing equilibrium in glucose solution within 40 s and quickly reverting to their initial state within 1 s after adding diluted hydrochloric acid. The PC sensor effectively generates optical signals across a broad glucose concentration range of 0-100 mM and realizes continuous glucose detection. Notably, they can indicate the risk of diabetes with artificial urine, which provides a strategy for noninvasive glucose detection. In addition, the adsorption and desorption processes of glucose on PC are monitored with a quartz crystal microbalance with dissipation, and the reversible swelling of the nanogel layer is revealed, which provides valuable references for the mechanism study of PC glucose sensors.