A simple electrochemical platform based on functional nucleic acids mediated DNA walker for detecting Pb2+ and malathion in environmental water and soil samples

Herein, a simple yet powerful label-free electrochemical sensing platform developed for dual detection of Pb²⁺ and malathion by ingeniously integrating Pb²⁺-dependent DNAzyme and malathion aptamer into a triplex DNA structure. The designed DNA complex not only served as dual recognition elements but also functioned as signal amplifiers through DNA walker activity triggered by target binding. When detecting Pb²⁺, the activated DNAzyme initiated cyclic cleavage of substrate DNA, thereby generating numerous G-quadruplex/hemin complexes that produced significantly enhanced electrochemical signal and achieved its signal-on detection. Following this, for malathion detection, the specific binding between the pesticide and its aptamer effectively disrupted the DNA walker assembly, consequently reducing signal output forming a signal-off detection mode. This innovative design successfully achieved highly sensitive and specific detection of both contaminants on a single platform through merely two operational steps while avoiding complex labeling procedures. Significantly, the sensor demonstrated consistently reliable performance in analyzing various challenging environmental samples including urban river water, agricultural water and soil samples. By combining nucleic acid recognition specificity with DNA walker signal amplification and straightforward operation, this advanced sensing platform presents remarkable potential for practical environmental monitoring of both Pb²⁺ and malathion.