Manganese(iii)meso-tetrakis(4-N-methylpyridyl)-porphyrin and mediator thionine co-decorated DNA nanowires for sensitive electrochemical monitoring of mercury(ii)

Abstract

We developed a novel electrochemical DNA biosensor for mercury(II) ion (Hg²⁺) detection on the basis of manganese(III) meso-tetrakis(4-N-methylpyridyl)-porphyrin (MnTMPyP) and electron mediator thionine (Thi) co-decorated DNA nanowires for signal amplification. The T-rich capture DNA assembled on the electrode could successfully immobilize the primer DNA via specific base-pairing, which triggered the hybridization chain reaction (HCR) to form long DNA nanowires with the aim of loading abundant MnTMPyP and electron mediator Thi. In the electrolyte containing H₂O₂, the MnTMPyP loaded in the DNA nanowires showed superior peroxidase-like activity and electrocatalyzed the reduction of H₂O₂, promoting the redox reaction of Thi with a dramatically amplified electrochemical signal. However, in the presence of target Hg²⁺, Hg²⁺-mediated thymine base pairs (T–Hg²⁺–T) are formed between the two neighboring T-rich capture DNAs, which resulted in the release of the MnTMPyP and Thi co-decorated DNA nanowires from the electrode surface, providing a reduced readout signal for the quantitative electrochemical detection of Hg²⁺. The results showed that the proposed electrochemical DNA biosensor was highly sensitive to Hg²⁺ in the concentration of 1.0 ng L⁻¹ to 10⁷ ng L⁻¹ with a detection limit of 0.5 ng L⁻¹ (2.5 pM), and it also exhibited excellent selectivity against other interferential metal ions.