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 (Hg) 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 SnS photoanode of the split G-quadruplex-hemin complex, the magnetic NiCoO@SiO-NH sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCoO@SiO-NH and then partly hybridized with another single-stranded DNA2 (S2). When Hg was present, the thymine-Hg-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 HO-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg. 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 SnS-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg 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 Hg in environmental fields.