Aptamer-functionalized 2D photonic crystal hydrogels for sensitive and selective Hg²⁺ detection

A two-dimensional photonic crystal hydrogel (2DPCH) sensor functionalized with aptamers has been developed for the highly sensitive detection of Hg²⁺ in water. The sensing mechanism relies on the specific formation of T- Hg²⁺-T hairpin structures between Hg²⁺ and the aptamers, inducing hydrogel contraction and altering the spacing between embedded two-dimensional photonic crystal microspheres. The Hg²⁺ concentration is determined by measuring changes in the diameter of the Debye diffraction rings. This method exhibits a detection range from 1 nM to 1 mM, with a limit of detection (LOD) of 0.65 nM and a strong linear correlation (R² = 0.9933). The sensor can be regenerated using 1 M HCl and reused multiple times without significant performance degradation. In spiked lake water samples, recovery rates ranged from 94.23% to 101.10%, with relative standard deviations (RSD) between 0.29% and 2.55%. This sensor demonstrates high sensitivity, excellent selectivity, reversibility, and requires only a laser pointer for operation, offering a novel strategy for the on-site rapid detection of heavy metal ions.