FRET-based colorimetric and ratiometric fluorescent probe for Hg²⁺ detection in water, soil, plants and live cells

Mercury is a highly toxic and globally pervasive pollutant. Once released into the environment, Hg²⁺ can be absorbed easily by plants and eventually accumulates in the human body through the food chain, causing severely damage to cell function and central nervous system. At present, most Hg²⁺ detection methods suffer low sensitivity, high cost, complex pre-processing process and limited application scope. Therefore, the development of an effective method for Hg²⁺ detection in different media is critical for environmental protection and human health safeguarding.

Herein, two novel FRET-based (Fluorescence Resonance Energy Transfer) fluorescent probes were successfully synthesized based on coumarin-rhodamine platform with glyoxal as the reactive group, RCHg-1 and RCHg-2, for Hg²⁺. They can detect Hg²⁺ quickly with high selectivity and sensitivity in colorimetric and ratiometric fluorescence detection mode, which can efficiently reduce interference from fluorescence self-absorption, instrument efficiency and environmental factor. The limits of detection (LODs) for Hg²⁺ were as low as nM level. Especially, the probe RCHg-2 had lower LOD of 1.39 nM. Water samples, soil and on-site test paper experiments for detecting Hg²⁺ were successfully implemented for practical application in environment. Furthermore, RCHg-2 possessed the ability to detect Hg²⁺ in onion epidermis, wheat, foxtail millet JinGu 21, mung bean, Arabidopsis thaliana and HeLa cells as a ratiometric fluorescent probe. All analysis data and detection phenomena proved that glyoxal is a perfect Hg²⁺ reactive group.

It is noteworthy that glyoxal was developed as the reactive group for ratiometric detection of Hg²⁺ for the first time in this work. This research work provides a potential chemical tool for early pollution monitoring and a new design strategy for effective detection of Hg²⁺ in complex environments and biological systems.