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 (R(2) = 0.99). The limit of detection for lead ions was 0.1 nM at a signal-to-noise ratio of 3.

Fluorescent detection of lead in environmental water and urine samples using enzyme mimics of catechin-synthesized Au nanoparticles

A facile, cost-effective, and sensitive fluorescent method for Pb²⁺ ion detection had been developed using catechin synthesized gold nanoparticles (C-Au NPs). The Pb-catechin complexes and Pb-Au alloys that formed on the C-Au NPs surfaces allowed NPs to exhibit peroxidase-mimicking catalytic activity in the H₂O₂-mediated oxidation of Amplex UltraRed (AUR). In 5 mM Tris-acetate buffers at pH 7.0, the H₂O₂-AUR-C-Au NP probe was highly selective (>100-fold) for Pb²⁺ ions in the presence of other tested metal ions (K⁺, Ag⁺, Na⁺, Cd²⁺, Ni²⁺, Ca²⁺, Hg²⁺, Sr²⁺, Co²⁺, Cu²⁺, Ba²⁺, Fe²⁺, Mg²⁺, Cr³⁺, and Fe³⁺ ions). The fluorescence intensity (excitation/emission maxima ∼540/588 nm) of the AUR product was proportional to the concentration of Pb²⁺ ions in the range of 10 nM-1.0 μM with a linear correlation (R² = 0.99). The H₂O₂-AUR-C-Au NP probe detected Pb²⁺ ions with a limit of detection (signal-to-noise ratio: 3) of 1.5 nM. The practicality of the H₂O₂-AUR-C-Au NP probe was validated for the determination of Pb²⁺ ion concentration in environmental water and urine samples, demonstrating its advantages of simplicity, selectivity, and sensitivity.