Luminescent Coordination Polymer with Ultrasensitive “Turn-On” Hg²⁺ Sensing Ability and Its Portable Hydrogel Test Kit

Hg 2+ has serious effects on ecosystems and human health. Thus, it is very important to develop simple and efficient methods to detect Hg 2+ . A luminescent coordination polymer (LCP) [Cd( L )(1-NA) 2 (H 2 O)·( L )(H 2 O) 0.5 ] n ( 1 ) was constructed by 5,5′-((9H-fluoren-9-ylidene)-methylene)dipyrimidine ( L ) and 1-naphthoic acid (1-NA) with rigid groups. 1 demonstrates a 1-D wave-like chain structure. Its fluorene and naphthalene groups from adjacent chains exist in π–π interaction. 1 has excellent water, pH, and thermal stability. It exhibits very rare and ultrahigh sensitive “turn-on” Hg 2+ sensing ability. Its detection limit toward Hg 2+ is extremely low (8.86 × 10 –8 M). Particularly, the fluorescence intensity of the water suspension of 1 (2.5 mL, 0.05 mg mL –1 ) can be rapidly enhanced by approximately 80 times after only adding Hg 2+ solution (200 μL, 1 mmol). Accordingly, 1 shows the lowest LOD and the highest emission enhancement in all LCP-based “turn-on” Hg 2+ sensors. Furthermore, 1 was immobilized in a hydrogel to fabricate a portable test kit to realize the convenient, fast, and quantitative Hg 2+ detection. This study provides an excellent sensor material and the first on-site platform for environmental monitoring of Hg 2+ .