Electric-Double-Layer-Modulation Microscopy

TL;DR

This paper introduces a microscopy technique that visualizes nanoscale electric double layer restructuring at liquid-solid interfaces by detecting changes in optical scattering, enabling label-free imaging and ionic current measurement at the single-ion level.

Contribution

It demonstrates a novel dark-field scattering microscopy method for real-time, nanoscale imaging of EDL dynamics and ionic currents without labels.

Findings

Nanoscale EDL restructuring can be detected via optical scattering.

The method measures ionic currents as low as a few attoamperes.

Spatially-resolved cyclic voltammetry is achieved.

Abstract

The electric double layer (EDL) formed around charged nanostructures at the liquid-solid interface determines their electrochemical activity and influences their electrical and optical polarizability. We experimentally demonstrate that restructuring of the EDL at the nanoscale can be detected by dark-field scattering microscopy. Temporal and spatial characterization of the scattering signal demonstrates that the potentiodynamic optical contrast is proportional to the accumulated charge of polarisable ions at the interface and its time derivative represents the nanoscale ionic current. The material-specificity of the EDL formation is used in our work as a label-free contrast mechanism to image nanostructures and perform spatially-resolved cyclic voltametry on ion current density of a few attoamperes, corresponding to the exchange of only a few hundred ions.