Cu(II)-coordinated GpG-duplex DNA as peroxidase mimetics and its application for label-free detection of Cu2+ ions

• DNA-based peroxidase mimetics assembled by polymorphic DNA and Cu2+ ions.
• Cu(II)-catalyzed oxidation reaction greatly accelerated by DNA scaffolds.
• Reaction rates greatly associated with secondary structures of DNA.
• Cu(II)-coordinated GpG-duplex DNA can sense Cu2+ ions in aqueous solution.
• The detection limit of 1.2 nM is achieved without significant interference.

Herein a facile method is proposed to construct DNA-based peroxidase mimetics simply assembled by polymorphic DNA and Cu2+ ions. The Cu(II)-catalyzed oxidation of TMB in the presence of H2O2 can be significantly accelerated through Cu(II)-coordination with DNA scaffolds, of which a colorimetric change can be discerned by naked-eye. The reaction rates of DNA–Cu(II) complexes are directly associated with sequence composition as well as the secondary structure of DNA scaffold, e.g., the reaction rate decreases in the following order: GpG-duplex≈G-rich coil>G-quadruplex>C-rich coil>i-motif. It is the first report to explore a colorimetric Cu2+ sensing system on the basis of peroxidase mimicking activities of polymorphic DNA-Cu(II) complexes. One of our most intriguing results is that the GpG-duplex DNA demonstrates the ability to sense Cu2+ ions in aqueous solution without significant interference from other metal ions. The Cu2+ detection limit of 1.2 nM is achieved with a linear response range of 1.2–100 nM, and the developed sensing system is potentially applicable for quantitative determination of Cu2+ in drinking water samples.

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