Electrocatalysis of ferricyanide reduction mediated by electron transfer through the DNA duplex: Kinetic analysis by thin layer voltammetry

Highlights: • Electrocatalysis of [Fe(CN)₆]^3- reduction by DNA-bound methylene blue was studied. • Kinetics of electrocatalysis was assessed by thin-layer voltammetry at stationary electrodes. • Theoretical approach allowed evaluation of DNA-mediated electron transfer (ET) rates. • Evaluated reaction rates were consistent with those obtained in the rotating disk electrode system. • Results offer simple tools for kinetic analysis of electrocatalysis involving DNA-mediated ET. -- Abstract: DNA-mediated electron transfer (ET) underlies a variety of bioelectronics applications, and, thus, simple approaches for its kinetic analysis are required. Here, electrocatalysis of a ferricyanide reduction catalyzed by methylene blue (MB) bound to either (dGdC)₂₀ or (dAdT)₂₅ duplexes tethered to gold via an alkanethiol linker was voltammetrically studied at stationary electrodes, and its kinetics was analyzed by two theoretical models. A thin layer voltammetry analysis, assuming that the reaction occurs within the l-nm thick layer formed by the DNA duplexes of the length l, yielded the electrocatalytic rate constant k₁ of (2.1 ± 0.4)10⁵ and (2.4 ± 0.5)10⁶ M⁻¹ s⁻¹, for (dGdC)₂₀ and (dAdT)₂₅. The sequence-specific k₁ values were consistent with structural differences of (dGdC)₂₀ or (dAdT)₂₅ at the negatively polarized interface and approached the k₁ previously reported for the rotating disk electrode system (Angew. Chemie Int. Ed. 58 (2019) 3048). These results offer new tools for immediate kinetic analysis of electrocatalytic reactions involving long-range ET along the DNA duplexes, the tools that allow differentiating electrical properties of nucleic acids in the most convenient and simple way.