Nanomolar concentrations of lead can be harmful to health, but current forms of detection are relatively insensitive and require sophisticated off-site analysis. Now, Jing Li and colleague Yi Lu have developed a DNA-based lead “probe” that can detect levels of the toxic metal ion between 10 nM and 4 μM using a simple fluorescence assay (J. Am. Chem. Soc. 122, 10466–10467, 2000). Double-stranded DNA forms a helix, but single strands can form folded structures with catalytic activity. Thousands of such catalytic DNA sequences were screened to find one (called 17E) that was sensitive to lead. When lead is present, the catalytic DNA cleaves a DNA–RNA substrate linked to a fluorophore, enhancing fluorescence. 17E was more than 80-fold more sensitive to lead than to other metal ions, and the signal was not reduced when equal quantities of other metal ions were present. Lu says that the next step is to create an array of DNA lead probes, each with differing affinities for lead, thereby improving the probe's sensitivity and reducing the risk of saturation. Practically, microfluidic technology or fiber optics could be used as platforms for the probes, offering robust and transportable detectors for this and other toxic ions.
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Fletcher, L. Catalytic DNA lead probe. Nat Biotechnol 19, 7 (2001). https://doi.org/10.1038/83583