A colorimetric and turn-on fluorescent chemosensor for selectively sensing Hg2+ and its resultant complex for fast detection of I− over S2−

• A colorimetric multifunctional sensor RBP was synthesized.
• The sensor exhibited a selective fluorescence enhancement response to Hg2+.
• The resultant sensor–Hg2+ complex rapidly detected I− over S2−.
• The sensor was successfully used to selectively detect Hg2+ in living cells.

A novel bipyridine-functionalized turn-on fluorescent chemosensor was successfully synthesized and fully characterized by 1H NMR, 13C NMR and MS, UV–vis and fluorescence spectroscopies. The sensor specifically binds to Hg2+ over other competing ions with a significant fluorescence enhancement as well as a visual colour change under physiological conditions. The detection limit of Hg2+ was as low as 32 nM, confirming very high sensitivity toward Hg2+. Moreover, the fluorescence intensity and colour change of the sensor-Hg2+ was quenched by I− or S2− and was proportional to their concentrations with a detection limit of 0.37 μM and 0.43 μM, respectively. The reaction of I− grabbing Hg2+ from the sensor–Hg2+ finished in 10 s due to a stronger binding force, much faster than that of S2−, which allowed fast detection of I− over S2− even in a competent environment. In addition, the sensor was successfully used for the highly sensitive detection of Hg2+ in living cells.

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