Electrocatalytic Mechanism for Improving Sensitivity and Specificity of Electrochemical Nucleic Acid-Based Sensors with Covalent Redox TagsPart I

The design and development of advanced electrocatalysis have been extensively explored for efficient energy conversion and electrochemical biosensing. Both ferricyanide (Fe­(CN)₆^3–) and methylene blue (MB) have been widely used in the development of electrochemical biosensing strategies. However, the electrocatalytic mechanism between nucleic acid-tethered MB and Fe­(CN)₆^3– remains unexplored. In this manuscript, we aim to provide readers in our community molecular insights into the electrocatalytic mechanism. The exploration of the electrocatalytic mechanism starts with a kinetic zone diagram for a one-electron homogeneous electrocatalytic reaction. Two factorsthe excess factor γ and the kinetic parameter λare important for a homogeneous electrocatalytic reaction; as such, we studied both. The excess factor parameter was controlled by applying Fe­(CN)₆^3– with various concentrations (50, 100, and 200 μM), and the kinetic parameter effect on the electrocatalytic process was examined by varying scan rates of cyclic voltammetry (CV) or frequencies of square-wave voltammetry (SWV). Moreover, we discovered that the probe dynamics of the nucleic acid tether is the third rate-limiting factor for the electrocatalytic reaction. As the probe dynamics switch of electrode-bound nucleic acid is often utilized as a mechanism in electrochemical nucleic acid-based sensors, we believe the electrocatalysis between nucleic acid-tethered MB and Fe­(CN)₆^3– is capable of enhancing sensitivity and specificity of electrochemical nucleic acid-based sensors with covalent redox tags.