An i-DNA based electrochemical sensor for proton detection

An i-DNA based electrochemical proton sensor which is fabricated by attaching the ferrocene-labeled i-DNA (Fc-i-DNA) onto a gold electrode is reported. This type of i-DNA is a cytidine-rich single-stranded oligonucleotide that its conformation can be switched between the random coil conformation and the folded i-motif structure at different pH values. The Fc-i-DNA is thiol terminated and can be bound to the gold electrode surface by Au–S interaction. With the variation of solution pH, the distance between ferrocene moiety and electrode surface is changed, leading to different redox currents. The pH can then be determined by measurement of the corresponding currents. In the range of pH 5.6–7.1, it is shown a linear relationship between the currents and pH values. The proton sensor also exhibits quick response, easy fabrication, and good selectivity.