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

A smarthydrogel grating detector with ultra-sensitivityand highselectivity is developed for real-time detection of trace hexavalentchromium ions [Cr(VI)] in water in a continuous-flow manner. The proposedhydrogel gratings possess poly(acrylamide-co-3-acrylamidopropyl-trimethylammoniumchloride) networks cross-linked by tetra-arm star poly(ethylene glycol)acrylamide(4-PEGAAm). In the hydrogel gratings, the tetra-alkylammonium groupsin the polymeric networks of the hydrogel grating can specificallycapture Cr(VI) via formation of ion pairs, while the 4-PEGAAm cross-linkersoffer 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 ofCr(VI) from dozens of interfering ions in water with an ultralow detectionlimit (10(-9) M) and fast response (<2 min). Thesmart hydrogel grating detector provides a promising detection platformfor analytic science.