A naphthalimide functionalized fluoran with AIE effect for ratiometric sensing Hg2+and cell imaging application

The pollution caused by mercury ions (Hg2+) poses a potential threat to public health. Therefore, monitoring Hg2+ concentration in the environment is necessary and significant. In this work, a naphthalimide functionalized fluoran dye NAF has been prepared, which shows a new red-shift in emission at 550 nm with the maximum intensity in a mixture of water-CH3CN (v/v = 7/3) due to aggregating induced emission (AIE) effect. Meanwhile, NAF can be employed as a Hg2+ ions sensor, which displays a selective and sensitive response to Hg2+ ions by the reduced fluorescence of naphthalimide fluorophore and increased fluorescence of fluoran group, respectively, showing ratiometric fluorescence signal changes with more than 65-fold emission intensity ratio increase and naked eyes visible color change. In addition, the response time is fast (within 1 min) and the sensing can be conducted in a wide pH range (4.0-9.0). Moreover, the detection limit has been evaluated to be 5.5 nM. The sensing mechanism may be attributed to the formation of a pi-extended conjugated system due to the Hg2+ ionsinduced conversion of spironolactone to the ring-opened form, partially accompanied by the fluorescence resonance energy transfer (FRET) process. Significantly, NAF exhibits suitable cytotoxicity to living HeLa cells, which allows it to be utilized for ratiometric imaging of Hg2+ ions assisted by confocal fluorescence imaging.

Automated summary

A naphthalimide functionalized fluoran dye NAF has been prepared, which exhibits a red-shift in emission at 550 nm in a water-CH3CN mixture due to aggregating induced emission (AIE) effect. NAF can function as a selective and sensitive sensor for Hg2+ ions by displaying a ratiometric fluorescence signal change and visible color change. It shows fast response time, wide pH range, and low detection limit, making it suitable for ratiometric imaging of Hg2+ ions in living HeLa cells.