Sensitive Hg2+ Sensing via Quenching the Fluorescence of the Complex between Polythymine and 5,10,15,20-tetrakis(N-methyl-4-pyridyl) Porphyrin (TMPyP)

The interaction between polythymine (dTn) and 5,10,15,20-tetrakis(N-methyl-4-pyridyl) porphyrin (TMPyP) was systematically studied using various techniques. dTn remarkably enhanced the fluorescence intensity of TMPyP as compared to other oligonucleotides. The enhanced fluorescence intensity and the shift of the emission peaks were ascribed to the formation of a pi-pi complex between TMPyP and dTn. And the quenching of the dTn-enhanced fluorescence by Hg2+ through a synergistic effect occurs due to the heavy atom effect. The binding of Hg2+ to TMPyP plays an important role in the Hg-TMPyP-dT(30) ternary complex formation. A TMPyP-dT30-based Hg2+ sensor was developed with a dynamic range of Hg2+ from 5 nM to 100 nM. The detection limit of 1.3 nM was low enough for Hg2+ determination. The sensor also exhibited good selectivity against other metal ions. Experiments for tap water and river water demonstrated that the detection method was applicable for Hg2+ determination in real samples. The Hg2+ sensor based on oligonucleotide dT(30)-enhanced TMPyP fluorescence was fast and low-cost, presenting a promising platform for practical Hg2+ determination.