How the electrochemical double layer manipulates molecule-metal interactions

Electrochemical interfaces are ubiquitous in sensing, catalysis and energy storage, yet understanding molecular interactions with the electrochemical double layer (EDL) remain limited. Here, we use electrochemical surface-enhanced Raman spectroscopy (EC-SERS) to probe analyte-EDL interactions in real time. Precision SERS electrodes with robust electrochemically-recleanable gold nanogaps allow us to detect subtle molecular spectral changes during cyclic voltammetry, revealing distinct intensity and frequency oscillations. Quantum mechanics/molecular mechanics simulations show that these effects arise from electrochemical potential-induced molecular reorientation and surface restructuring, driven by dynamic interactions with the EDL. For sensing, this mechanism reduces detection limits for DNA nucleobases by over 25-fold and enables label-free multiplexed sensing. Beyond improved sensor performance, this work resolves long-standing puzzles in understanding EC-SERS and gives new insight into neutral molecule behaviour within the EDL.