Quantum Tunneling Currents in a Nanoengineered Electrochemical System

We develop an equivalent circuit model for charge transfer across a nanoscale electrochemical interface and apply it to tune the interface parameters so that tunneling electrons transduce information about the vibronic structure of the interface. Model predictions are broadly consistent with cyclic voltammograms acquired using a custom, low-noise potentiostat on a 50 nm diameter Pt(80%)–Ir(20%) electrode functionalized with 10 nm diameter gold nanoparticles and immersed in a phosphate buffer with a redox couple. Conductance–voltage sweeps for 1 μM 2-d-leucine have shifted vibronic peaks from those for 1 μM leucine, indicating promise for label-free sensing. The model is based on two interdependent lengths that describe the interaction strengths between the participant electronic states in the electrolyte and the participant reaction coordinates, and between the latter and the surrounding bath modes. These lengths translate into capacitive elements which are positioned in parallel to the classical capacita...