Hairpin oligonucleotides anchored terbium ion: a fluorescent probe to specifically detect lead(II) at sub-nM levels

A terbium based fluorescent probe was synthesized by coordinating terbium ions with a designed oligonucleotides (5′-ATATGGGGGATAT-3′, termed GH5). GH5 improved the fluorescence of terbium ions by four orders of magnitude. The fluorescence enhancement of terbium ions by different oligonucleotides sequences indicated that the polyguanine loop of the hairpin GH5 is key to enhance terbium ion emission. The quantum yield of Tb–GH5 probe was 10.5% and the probe was photo-stable. The result of conductivity titration indicated that the stoichiometry of the probe is 3.5 Tb: 1 GH5, which is confirmed by fluorescence titration. This probe had high sensitivity and specificity for the detection of lead ions. The fluorescence intensity of this probe was linear with respect to lead concentration over a range 0.3–2.1 nM (R2 = 0.99). The limit of detection for lead ions was 0.1 nM at a signal-to-noise ratio of 3.