Efficient Detection of Hyperkalemia with Highly Transparent and Ion-Recognizable Hydrogel Grating Sensors

A novel detection method based on highly transparent and ion-recognizable hydrogel grating sensors is developed for efficient diagnosis of hyperkalemia in this work. The proposed hydrogel gratings are made of poly(N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) (poly(NIPAM-co-B15C5Am)) networks by using tetra-arm-polyethylene-glycol-acrylamide (tetra-arm-PEGAAm) as a macromolecular cross-linker. The macromolecular cross-linker tetra-arm-PEGAAm can prevent the microstructure inside the poly(NIPAM-co-B15C5Am) hydrogel networks changing from the homogeneous state to the heterogeneous state during the response processes, which ensures the high transparency of hydrogel gratings as well as the strong laser intensity through the diffraction gratings during the response processes. The pendent crown ether 15-crown-5 units on the polymer networks in hydrogel can specifically recognize K+ to form stable 2:1 “sandwich” host–guest complexes, which cause the height shrinkage of hydrogel gratings. By using a simple optical detection system, the proposed poly(NIPAM-co-B15C5Am) hydrogel grating sensor can realize a highly selective and sensitive detection of K+ concentrations in both water and real human serum. Due to the specific host–guest complexation between crown ether 15-crown-5 and K+, the detections of K+ concentrations in aqueous solutions are nearly not interfered by other metal ions. Furthermore, because of the rapid response of the nanostructured poly(NIPAM-co-B15C5Am) hydrogel gratings, the diagnosis of hyperkalemia can be achieved within 3 min. The proposed smart hydrogel grating sensors in this work can be applied for rapid and efficient detection of hyperkalemia, and the results in this work provide valuable guidance for the development of novel smart sensors.