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

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.