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.