Optical Detection of Lead(II) Ions Using DNA-Based Nanosensor

Lead (Pb) is a highly toxic metal that tends to accumulate in the body. The complexes of lead are very stable within the body and cannot be metabolized or degraded rapidly, leading to lead toxicity. Therefore, it is important to detect low levels of lead in the environment to prevent lead poisoning in humans. The detection of Pb²⁺ ions at the nanomolar and micromolar level is achieved using DNA aptamers and quantum dots. Pb²⁺ ions can be detected using a DNA aptamer known as thrombin binding aptamer (TBA), which folds into a G-quadruplex structure when lead is present. The conjugation of a quantum dot and a gold nanoparticle (AuNP) to the TBA allows for optical detection via fluorescence resonant energy transfer. In the aptamer probe discussed herein, the excited quantum dot fluoresces when the DNA is in a random coil configuration. Once the Pb²⁺ ion-induced folding occurs, the fluorescence is reduced through energy transfer to the AuNP. The quenching efficiency observed with the liquid assay probe and the filter paper probe at 1-ţM Pb²⁺ ions is 41% and 71%, respectively.