Fluorescence detection of lead(II) ions through their induced catalytic activity of DNAzymes

We have developed a fluorescence approach for the highly selective and sensitive detection of Pb²⁺ ions using AGRO100, a G-quadruplex DNAzyme. The sensing strategy is based on Pb²⁺ ions inducing increased DNAzyme activity of AGRO100 in the presence of hemin, which acts as a cofactor to catalyze H₂O₂-mediated oxidation of Amplex UltraRed (AUR). A test of eight aptamers of various sequences for the detection of Pb²⁺ ions revealed that AGRO100 performed the best in terms of sensitivity. The AGRO100-AUR probe exhibited high selectivity (>100-fold) toward Pb²⁺ ions over other tested metal ions. The fluorescence intensity (excitation/emission maxima, ca. 561/592 nm) of the AUR product was proportional to the concentration of Pb²⁺ ions over the range 0-1000 nM, with a linear correlation (R² = 0.98). For 5 mM Tris-acetate (pH 7.4) solutions in the presence and absence of 100 mM NaCl, the AGRO100-AUR probe provided limits of detection (signal-to-noise ratio = 3) for Pb²⁺ ions of 1.0 and 0.4 nM, respectively. We validated the practicality of the use of the AGRO100-AUR probe for the determination of the concentrations of Pb ²⁺ ions in soil samples. This approach allows the determination of the concentrations of Pb²⁺ ions with simplicity, selectivity, and sensitivity.