An "Off-On" Rhodamine 6G Hydrazide-Based Output Platform for Fluorescence and Visual Dual-Mode Detection of Lead(II)

In this study, the rhodamine 6G hydrazide (R6GH) complex was synthesized to develop an "off-on" output platform for fluorescence and visual dual-mode analysis of lead(II) (Pb²⁺). The prepared R6GH complex using the heat to reflux reaction of rhodamine 6G (R6G) and hydrazine hydrate was characterized through FT-IR, MS, ¹H NMR, and ¹³C NMR and demonstrated to have good fluorescence stability and reversibility. The microenvironment for Pb²⁺ detection has been optimized in detail. Under the optimal conditions, the "off-on" R6GH-based fluorescence output platform showed a good response to Pb²⁺ in the concentration range of 0.05-6.0 μM (R² = 0.9851) with a limit of detection (LOD) of 0.02 μM. Furthermore, at three spiked Pb²⁺ levels in the selected agricultural (tap water, soil) and food (fish, shrimp) samples, the developed R6GH-based fluorescence assays obtained a significant recovery range of 84.0-102.0% (RSD < 5.0%, n = 3), which had a good correlation with the results from ICP-MS (R² = 0.9915). The developed R6GH immobilized paper-based array sensor can reach the lower LOD (2.5 μM) for Pb²⁺ through the naked eye. By combining with LAB analysis, a good linear response was obtained in the Pb²⁺ concentration range of 1.0-50.0 μM. These results indicated that the developed R6GH probe had great application potential in accurate detection of fluorescence and rapid visual and semiquantitative screening for Pb²⁺.