A Rhodamine-naphthalimide conjugated chemosensor for ratiometric detection Hg²⁺ in actual aqueous samples

A novel chemosensor (RSNA) based on 1,8-naphthalimide fluorescent group and Rhodamine B was designed and synthesized for sensing Hg²⁺. As a ratiometric chemosensor, the probe system exhibits high affinity for Hg²⁺ based on fluorescence resonance energy transfer (FRET) mechanism. When RSNA interacts with Hg²⁺ in actual medium, accompanied by a significant color change from colorless to pink, and a light to orange fluorescence change. Meanwhile, RSNA shows a typical FRET signal from the 1,8-naphthalimide group to the Rhodamine group, a new emission peak appears at 585 nm and the emission peak at 381 nm decreases in the fluorescence spectrum. In addition, upon interaction with Hg²⁺, RSNA showed a 1:1 stoichiometry for the complex, the mechanism of interaction between RSNA and Hg²⁺ was also verified by ESI-MS, fluorescence and UV–vis spectra. Importantly, studies reveal that RSNA could be used for ratiometric detecting Hg²⁺, and a low detection limit of 0.059 μM in actual medium. Futher, the probe was suitable for sensing Hg²⁺ in river water due to its real-time response, high recovery rate, and anti-interference property.