Nanoimpedimetry with plasmonic nanoparticles

This paper introduces a new nanosensor that can record electrical currents optically. We demonstrate a robust non-fluorescent approach via chemically stable metallic nanoparticles that promises to enable electrical measurements in complex environments. This is becoming increasingly important in several fields such as electrochemistry, electrophysiology and bioelectricity. The sensing principle is based on the well-known sensitivity of localized surface plasmon resonance to changes in interfacial charge density. Here, we present a new approach that enables quantitative imaging of charge density dynamics at the metal-electrolyte interface of plasmonic nanoparticles. To achieve this, we employed a modelling approach that combines Mie scattering and double-layer capacitor models of the metal-electrolyte interface to convert the intensity of voltage-modulated light scattering by single nanoparticles to charge density modulation. Voltage-modulated single-wavelength micro-spectroscopy was performed to map the charge density modulation of gold nanoparticles attached to a substrate. The reported quantitative imaging method was validated using finite-element models of electrical properties of single plasmonic nanoparticles. Our findings pave the way for rigorous electrical, electrochemical and biochemical sensing using plasmonic nanostructures