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

• Three dimensional ordered macroporous (3DOM) Au–Pd bimetallic electrode was fabricated via electro-controlled co-reduction method.
• Target-induced DNAzyme biosensor for Pb2+ detection.
• Methylene blue-single walled carbon nanotubes (MB-SWCNTs) as signal reporter leading to a lower background current signal.
• Ultrasensitive detection of Pb2+ with a liner range covering 14 orders of magnitude and a limit of 1×10−19 M.
• The biosensor was applied to determine Pb2+ in serum samples with satisfactory results.

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 (1×10–19 M) 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 1×10–17–1×10−4 M. 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.