Ultrasensitive diffraction gratings based on smart hydrogels for highly selective and rapid detection of trace heavy metal ions

Abstract

An ultrasensitive grating system based on stimuli-responsive hydrogels with ultra-low detection limit for highly-selective and rapid detection of trace heavy metal ions is developed. The excellent detection performance of trace heavy metal ions is demonstrated by using poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) hydrogel gratings with well-designed molecular structures for detecting trace Pb²⁺ in water. The hydrogel grating with nanometer-sized height synergistically combines the fast thermo-responsive volume phase transition of poly(N-isopropylacrylamide) backbones and the highly-selective Pb²⁺ recognition of benzo-18-crown-6 moieties to achieve enhanced Pb²⁺-induced swelling changes for detecting trace Pb²⁺. By integrating the hydrogel grating into a simple optical detection system, the signal of trace Pb²⁺ can be efficiently converted and amplified into optical intensity signals for ultrasensitive, highly-selective and rapid detection of Pb²⁺ with concentration as low as 10⁻⁹ M. This hydrogel grating system provides an efficient strategy for ultrasensitive detection of trace heavy metal ions for protection of the environment and human health.