Highly sensitive fluorescent sensor for mercury ion based on photoinduced charge transfer between fluorophore and π-stacked T–Hg(II)–T base pairs

A novel and simple oligodeoxyribonucleotide-based sensor with single fluorophore-labeled for mercury ion sensing was reported. An oligodeoxyribonucleotide poly(dT) was labeled with fluorescein as donor. Based on the specific binding of Hg(II) to T–T mismatch base pairs, the formation of π-stacked [T–Hg(II)–T] with “sandwich” structure on the addition of Hg(II) ions facilitates the electron transfer via photoinduced charge transfer (PCT), which creates an additional nonradiative decay channel for excited fluorophore and triggers the fluorescence to be quenched. The π-stacked [T–Hg(II)–T] functioned not only as mercury ion recognition but also as an electron acceptor to quench the donor. A linear relationship was observed over the range of 0–1.0 μM with the detection limit of 20 nM for mercury ions. The fluorescence quenching phenomenon and quenching mechanism, reliability and selectivity of the system were investigated in detail.