Colorimetric and Photocurrent-Polarity-Switching Photoelectrochemical Dual-Mode Sensing Platform for Highly Selective Detection of Mercury Ions Based on the Split G-Quadruplex–Hemin Complex

Mercury ion (Hg2+) is one of the most harmful heavy metal ions with the greatest impact on public health. Herein, based on the excellent catalytic activity toward 3,3′,5,5′-tetramethylbenzidine (TMB) and the strong photocurrent-polarity-switching ability to SnS2 photoanode of the split G-quadruplex–hemin complex, the magnetic NiCo2O4@SiO2–NH2 sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg2+ assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCo2O4@SiO2–NH2 and then partly hybridized with another single-stranded DNA2 (S2). When Hg2+ was present, the thymine–Hg2+–thymine base pairs between S1 and S2 were formed, causing the formation of the split G-quadruplex in the presence of K+. After addition of hemin, the split G-quadruplex–hemin complex was obtained and effectually catalyzed the H2O2-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg2+. The linear response range is 10 pM to 10 nM, and the detection limit is 3.8 pM. Meanwhile, the above G-quadruplex–hemin complex effectively switched the photocurrent polarity of SnS2-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg2+ with a linear response range of 5 pM to 500 nM and a detection limit of 2.3 pM. Moreover, the developed dual-mode sensing platform provided mutual authentication of detection results in different modes, effectively improving the assay accuracy and confidence, and may have a good potential application in highly sensitive, selective, and accurate determination of Hg2+ in environmental fields.