100.0 equiv. of Hg2+ to the solutions containing MS5 (2.5 μM) and the appropriate metal ions (100.0 equiv.) (λex = 540 nm).
Moreover, the Hg2+-sensing ability of MS5 in a wide range of pH values was also investigated. As depicted in Fig. S4, MS5 alone
was inert to pH in the range of 4.5-10.5. On the other hand, it still responded to Hg2+ sensitively within this pH range (4.5-9.1). These
results indicate that MS5 could be used in neutral natural systems, or a mildly acidic or basic environment.
For practical purposes, the detection limit of MS5 for the detection of Hg2+ was also an important parameter. The fluorescence
titration curve revealed that the fluorescence intensity of MS5 at 581 nm increased linearly with the amount of Hg2+ in the 0-50.0 μM
range (R2 = 0.99) (Fig. S5, ESI†). Thus, the detection limit of MS5 for Hg2+ was calculated to be 5.70 × 10-9 M (Hg2+ content = 1.2
ppb), which was below the US Environmental Protection Agency (EPA) threshold in safe drinking water (2.0 ppb).16 These results
showed that MS5 could be a sensitive fluorescent probe for the quantitative detection of Hg2+.
To further investigate the practical application of MS5, we prepared test strips by immersing filter paper into the water solution of
MS5 (1.0 mM) and then dried in air. When dipped into the solutions of Hg2+ ions with different concentrations, the test strips containing
MS5 demonstrated apparent orange-fluorescence excited at 365 nm under a UV lamp, and the discernible concentration of Hg2+ ions
could be as low as 10 μM (Fig. S7, ESI†). Thus, these strips could be conveniently handled at any moment for the detection of Hg2+
ions.
3. Conclusions
In conclusion, we have rationally developed a benzoBODIPY-based sensitive fluorescence probe, MS5, for the detection of Hg2+ in
neutral aqueous solution via PeT mechanism. The probe has the unique advantages of excellent selectivity and sensitivity, and fast
response towards Hg2+, with a low detection limit (5.7 nM). We anticipate that the experimental results of this study will inspire the
future designing of heavy metal ion sensors for a variety of chemical and biological applications.
Acknowledgments
This work was supported by Zhejiang Provincial Natural Science Foundation of China (Grant No. LY17B070008), Science
Foundation of Zhejiang Sci-Tech University (Grant No. 15062174-Y), and the Project Grants 521 Talents Cultivation of Zhejiang Sci-
Tech University.
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