Oligonucleotide-Based Reusable Electrochemical Silver(I) Sensor and Its Optimization via Probe Packing Density

We report herein a selective, sensitive, and reusable electrochemical sensor for the detection of silver(I) ions. This sensor detects Ag⁺ through a structure-switching electrode-bound DNA by measuring the changes in the electron-transfer efficiency. A single-stranded DNA, featuring a methylene blue (MB)-tagged DNA hairpin structure, strategically provides selective binding for the silver-mediated coordination of cytosine-Ag⁺-cytosine complexes. The DNA-modified electrode produces a change in the electrochemical signal due to the redox current of the surface-confined MB tag. The "turn-on" signaling upon silver(I) ion binding could be attributed to a conformational change in the MB-tagged DNA from an open structure to a target-induced folding structure. Differential pulse voltammetry of the DNA-modified electrode showed that the MB reduction signal increased linearly with an increase in Ag⁺ concentrations in a range of 10-200 nM, with a detection limit of 10 nM. The structure-switching silver(I) ion sensor was amenable to regeneration by simply unfolding the electrode-bound MB-tagged DNA in 100 mM ethylenediaminetetraacetic acid, and it could be regenerated with no loss in signal gain upon subsequent silver(I) ion binding. We also demonstrated that by controlling the probe packing density on the electrode surface, the fabrication parameters can be varied to achieve optimal sensor performance.