Electrochemical sensor based on Au nanoparticles decorated boron-doped diamond electrode using ferrocene-tagged aptamer for proton detection

An electrochemical sensor based on a boron-doped diamond (BDD) electrode decorated with gold nanoparticles (Au-NPs) was developed for the detection of protons using a ferrocene-tagged (Fc-tagged) aptamer. By introducing the Au-NPs, the aptamer with a thiol-terminated group was immobilized on the Au-NPs/BDD electrode by Au-S interaction. Morphology and characteristics of the modified BDD electrode were analyzed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The employed aptamer is a cytosine-rich single stranded oligonucleotide. In this oligonucleotide, the distance between the labeled redox moiety and the electrode changes with the pH value because of the formation of an i-motif structure from cytosine-protonated cytosine (C–C+) pairs. The pH influenced the electron transfer process and the redox current. The synergetic effects of the BDD electrode and the Au-NPs improved the performance of this sensor. Therefore, the Au-NPs/BDD electrode exhibited higher sensitivity, faster response, a wider linear range and a good reproducibility for the detection of proton compared with the planar Au electrode.

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► An electrochemical pH sensor was developed using a ferrocene (Fc)-tagged aptamer.
► An aptamer with cytosine-rich single strand forms an i-motif structure at low pH.
► The distance between the redox moiety and the electrode changes with the pH value.
► The pH influenced the electron transfer process and the redox current.