Target-induced electronic switch for ultrasensitive detection of Pb²⁺ based on three dimensionally ordered macroporous Au-Pd bimetallic electrode

A novel strategy for selective and sensitive amperometric detections of Pb²⁺ was proposed based on the three dimensional ordered macroporous (3DOM) Au-Pd bimetallic electrode and target-induced methylene blue-single walled carbon nanotubes (MB-SWCNTs) as signal reporter. A DNA biosensor was fabricated by immobilizing capture probe DNA on the 3DOM Au-Pd bimetallic electrode, which further hybridized with the reporter DNA loaded on the MB-SWCNTs adduct upon the exposure of Pb²⁺, inducing measurable electrochemical signal. Due to the dramatic signal amplification by the enhanced immobilization of DNA on the surface of 3DOM Au-Pd bimetallic electrode and MB-SWCNTs, coupling the low background signal produced by blank solution, ultra-low level (1×10^-19M) of Pb²⁺ could be detected. Under the optimal conditions, the electrochemical signal of the MB increased with the increasing Pb²⁺ concentration, exhibiting a linear response in the range of 1×10^-17-1×10^-4M. Furthermore, with the application of Pb²⁺ dependent DNAzyme, the proposed sensing system demonstrated high selectivity. This work represented a promising potential for on-site testing Pb²⁺ in real drinking water and serum sample analysis.