An electrochemical sensing strategy based on a three dimensional ordered macroporous polyaniline-platinum platform and a mercury(II) ion-mediated DNAzyme functionalized nanolabel

A highly sensitive electrochemical sensor for the detection of mercury(II) ions (Hg²⁺) was developed by using a three dimensional ordered macroporous polyaniline-platinum (3DOM PANI-Pt) composite film as a sensing platform. 3DOM PANI-Pt was realized by electrochemical co-deposition of Pt nanoparticles and PANI into the sacrificed silica template through the redox reaction involving the monomer aniline (AN) and PtCl₆^2-. The G-rich oligonucleotide strand functionalized Au nanoparticle was employed as the Hg²⁺-mediated structural switch and to enhance the sensitivity. In the absence of Hg²⁺, the oligonucleotide strand formed an intramolecular duplex where the G-rich sequence was partially caged. In the presence of Hg²⁺, the release of the G-rich sequence was observed due to the stabilization of T-Hg²⁺-T, which formed an active G-quadruplex DNAzyme and catalyzed the reduction of H₂O₂. Under the optimal conditions, the current signal of H₂O₂ increased with increasing Hg²⁺ concentration in the dynamic range from 10^-13 to 10^-6 M, and the detection limit up to 8.7 × 10^-14 M was seen. Further, the sensor was successfully utilized for the determination of Hg²⁺ in an authentic aquatic sample, with an acceptable accuracy compared to the method commercially available. In this paper, we proposed a general and simple strategy because only one oligonucleotide strand was required for both Hg²⁺ recognition and signal amplification, potentially allowing the detection of other metal ions or trace pollutants in environmental matrices by simply employing various DNA or aptamer probes.