Highly Sensitive Hydrogel Gratings for Real-Time Detection of Trace Hexavalent Chromium Ions in Water

Abstract

A smart hydrogel grating detector with ultra-sensitivity and high selectivity is developed for real-time detection of trace hexavalent chromium ions [Cr­(VI)] in water in a continuous-flow manner. The proposed hydrogel gratings possess poly­(acrylamide-co-3-acrylamidopropyl-trimethylammonium chloride) networks cross-linked by tetra-arm star poly­(ethylene glycol)­acrylamide (4-PEGAAm). In the hydrogel gratings, the tetra-alkylammonium groups in the polymeric networks of the hydrogel grating can specifically capture Cr­(VI) via formation of ion pairs, while the 4-PEGAAm cross-linkers offer hydrogel grating with good transparency and mechanical properties. With rationally designed molecular structures and surface relief microstructures, the hydrogel grating detector enables highly selective detection of Cr­(VI) from dozens of interfering ions in water with an ultralow detection limit (10–9 M) and fast response (<2 min). The smart hydrogel grating detector provides a promising detection platform for analytic science.