A novel “naked-eye” and ratiometric fluorescent Hg 2+ probe based on thiourea−thiadiazole−pyridine linked (TTP) fluorescent organic nanoparticles (FONs) was designed and synthesized. TTP FONs show good water solubility; a 46-fold increase in fluorescence quantum yield, high selectivity for sensing, and a 98 nm red shift of the fluorescence emission upon binding Hg 2+ in aqueous media are observed. Under the optimum conditions, the relative fluorescence intensity ratio, I 501 / I 403, is increased linearly with the increasing logarithmic concentration of Hg 2+ in the range of 2.5−40 μM with a detection limit of 1.13 × 10 −7 M (22.6 ppb), whereas the fluorescence intensity of TTP FONs to other metal ions, including Na +, Ca 2+, Ni 2+, Cd 2+, Cu 2+, Ag +, Pb 2+, Mn 2+, and Mg 2+, is negligible. The possible mechanism is discussed.
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Li et al. (2009) studied this question.