Random walk on a leash: a simple single-molecule diffusion model for surface-tethered redox molecules with flexible...

Area of Science:

• Electrochemistry
• Physical Chemistry
• Computational Chemistry

Background:

• Understanding the electrochemical behavior of single molecules is crucial for advanced sensing and molecular electronics.
• Surface-confined molecules exhibit complex dynamics influenced by tethering and diffusion.
• Existing models often lack the ability to fully capture the interplay between molecular motion and electrochemical response.

Purpose of the Study:

• To develop a versatile random walk model for simulating single-molecule electrochemical responses.
• To investigate the impact of molecular tether length and diffusion on voltammetric behavior.
• To predict and understand the electrochemical response of surface-confined redox molecules with motion.

Main Methods:

• Development of a 3D random walk model for Brownian motion simulation.
• Incorporation of distance- and potential-dependent electron transfer probabilities.
• Generation of cyclic voltammograms by simulating electron transfer events.
• Validation of the model using redox-active methylene blue tethered by DNA.

Main Results:

• The model accurately simulates electrochemical responses, transitioning between adsorbed and diffusion-limited regimes.
• Peak current dependence on scan rate shifts from linear (adsorbed) to square root (diffusion-limited).
• The transition regime is identified when diffusion layer thickness is approximately 10 times the tether length.
• The model successfully predicts the voltammetric behavior of methylene blue tethered by DNA.

Conclusions:

• The developed random walk model provides a powerful tool for studying surface-confined redox molecules.
• Molecular motion significantly influences electrochemical response, with distinct regimes observed at different scan rates.
• The model enables the estimation of diffusion coefficients for end-tethered molecules, offering insights into their dynamics.