Tracking Nanoelectrochemistry Using Individual Plasmonic Nanocavities

Abstract

We study in real time the optical response of individual plasmonic nanoparticles on a mirror, utilized as electrodes in an electrochemical cell when a voltage is applied. In this geometry, Au nanoparticles are separated from a bulk Au film by an ultrathin molecular spacer. The nanoscale plasmonic hotspot underneath the nanoparticles locally reveals the modified charge on the Au surface and changes in the polarizability of the molecular spacer. Dark-field and Raman spectroscopy performed on the same nanoparticle show our ability to exploit isolated plasmonic junctions to track the dynamics of nanoelectrochemistry. Enhancements in Raman emission and blue-shifts at a negative potential show the ability to shift electrons within the gap molecules.

Metal‐Dielectric Nanocavity for Real‐Time Tracing Molecular Events with Temperature Feedback

“…It should be noted that the electric and magnetic field enhancement is strongly dependent on the NP diameter at fixed wavelength (Figure a, b), providing maxima values at the NP diameters of ∼160, 190, 240, and 280 nm. These numerical results correlate with experiment on light scattering by such NPs in dark field geometry (see Supporting Information, Figure S3), where the intrinsic NP optical resonances and pump/scattering are merged …”

“…Despite high thermal stability of dielectrics within broad temperature range, applicability of such nanoscale Raman thermometers for the most of chemical and biological processes is hindered by relatively long data acquisition time (hundreds of second for commercial Raman spectrometers), which is due to low RS signal intensity from non‐resonant nanometer scale objects.…”

“…In light of the multifunctionality of the hybrid nanocavity, its performance should be critically discussed in details. We compare our design with numerous approaches to nanoscale thermometry, heating and monitoring of molecular events, which have been developed for biomedical, cell biological and chemical applications, as well as for material science, physics, and engineering of nanodevices (i)Despite the diameter of the focused radiation (860 nm) we use in Raman measurements is much greater than the average diameter of NPs (100‐300 nm), most of the collected RS signal (Figure c) originates from the BSA molecules hosted inside the nanocavity (inset in Figure c).…”

“…Nanometer scale gap between metallic film and adjacent plasmonic nanoparticle (NP) ensures extremely localized and enhanced optical field . Such plasmonic nanocavity brings unique opportunities for strong light‐matter interaction, enhancement of Purcell factor and Raman scattering (RS), as well as for lasing, bio‐sensing, and initiation/monitoring the molecular events . However, the interaction of light with such nanocavity is accompanied by inevitable heating due to Joule losses resulting in irreversible modification of shape, composition and optical properties of the metallic components .…”

“…[1][2][3] Such plasmonic nanocavity brings unique opportunities for strong light-matter interaction, [4] enhancement of Purcell factor [5,6] and Raman scattering (RS), [7][8][9][10] as well as for lasing, [11] biosensing, [12] and initiation/monitoring the molecular events. [13][14][15][16] However, the interaction of light with such nanocavity is accompanied by inevitable heating due to Joule losses [17] resulting in irreversible modification of shape, composition and optical properties of the metallic components. [18][19][20] This motivates to seek for alternatives for localization and enhancement of light when the local temperature plays a crucial (positive or negative) role.…”