Electronic synergy between ligands of luminol and isophthalic acid for fluorescence ratiometric detection of Hg.

Stimulus-responsive double-ligand luminol-Eu-IPA infinite coordination polymer nanoparticles (luminol-Eu-IPA CPNPs) were prepared as a ratiometric fluorescence probe for highly selective detecting Hg. The CPNPs were constituted of Eu as the nuclear metal coordinated by isophthalic acid (IPA) together with luminol as an auxiliary ligand. The photoinduced electron transfer (PET) occurring from IPA to luminol prevented the antenna effect between IPA and Eu, leading to the quench fluorescence of Eu under light excitation. As Hg has a high affinity to N atom of luminol and the spin-orbit coupling effect, spectroscopically and magnetically silent properties, the fluorescence intensity of luminol was quenched. Meanwhile, the PET effect between luminol and IPA was interrupted under the presence of Hg. This process resulted in a significant decrease in the fluorescence intensity of luminol and a significant increase in the fluorescence intensity of Eu. Therefore, the fluorescence ratiometric detection of Hg was performed by monitoring the ratio of the fluorescence at 617 nm of Eu to that at 430 nm of luminol. The linear range was from 0.05 to 20 μM with a detection limit as low as 13.2 nM Hg (S/N = 3). Due to the fluorescence of luminol be quenched and the effect of PET be disrupted simultaneously, the probe exhibiting excellent detection selectively can avoid false positive signals, which was demonstrated for monitoring mercury ions in real water samples. Precision in positioning ligands in CPNPs is an advantage to achieve high specificity in comparison to traditional organic dendrimers or precious metal nanomaterials.