Voltage-Induced Adsorbate Damping of Single Gold Nanorod Plasmons in Aqueous Solution

Abstract

Unbiased gold nanoparticles are negatively charged in aqueous solution but not hydrated. Optical spectroscopy of voltage-clamped single gold nanoparticles reveals evidence that anion adsorption starts at positive potentials above the point of zero charge, causing severe but reversible plasmon damping in combination with a spectral red shift exceeding the linear double layer charging effect. Plasmon damping by adsorbate is relevant for the use of nanoparticles in catalysis, in biodiagnostics, and in surface enhanced Raman scattering.

Single-Particle Plasmon Voltammetry (spPV) for Detecting Anion Adsorption

“…7-10 As demonstrated via ensemble spectroscopy, nanoparticle plasmons report on their local dielectric environment (nanometer range), 11-13 and thus make ideal candidates for electrochemical reaction sensing. 4,10,[14][15][16][17][18][19][20] We seek to develop an optical method for monitoring electrochemical reactions at individual nanoparticles that would allow parallel monitoring of many nanoparticles in situ.Potential-controlled sulfate ion adsorption to gold is useful for demonstrating plasmonbased sensing because there are multiple benchmark examples. Bulk spectroelectrochemical methods have been successful in sensing sulfate adsorption on planar gold electrodes via second harmonic generation (SHG), 21 two dimensional Fourier transform infrared spectroscopy (2D FTIR), 22 and surface enhanced Raman spectroscopy (SERS).…”

“…49,67 The consistent decrease in Γ at anodic potentials is an important observation in that the application of anodic potentials typically leads to a broadening of nanoparticle plasmon resonances. 10,[14][15][16][54][55][56][57] The system studied here is unique however as we are probing a charge transfer plasmon. Electrochemical tuning of such a touching nanosphere/film system has not been modelled in the literature, but may merit theoretical study page 6 of 20 for its potential to probe changes in the plasmonic density of states using an experimentally feasible system with a simple yet highly tunable geometry.…”

“…[7][8][9][10] As demonstrated via ensemble spectroscopy, nanoparticle plasmons report on their local dielectric environment (nanometer range), [11][12][13] and thus make ideal candidates for electrochemical reaction sensing. 4,10,[14][15][16][17][18][19][20] We seek to develop an optical method for monitoring electrochemical reactions at individual nanoparticles that would allow parallel monitoring of many nanoparticles in situ.…”

Quantum description of the optical response of charged monolayer–thick metallic patch nanoantennas

“…The induced electron density ∆n DP (r) = n(r, t * ) − n(r, t = 0) is obtained from the time-dependent electron density n(r, t) by exposing the system to the linearly z-polarized electromagnetic wave with frequency Importantly, when Q electrons are added to the system, the change of the absorption spectra predicted by the classical theory, is not confirmed by the TDDFT calculations even qualitatively. Indeed, for the 2D-systems it is commonly assumed that the extra charge is homogeneously distributed over the nanoobject [26][27][28][47][48][49][50][51] , so that the plasmon frequency changes as ∆w p /w p = 0.5Q/N e . Thus, within this assumption, in the classical calculations the plasmon modes experience a blue-shift with increasing Q as shown in Fig.…”

“…In this context, understanding of the quantum/classical correspondences in individual and coupled plasmonic systems when they are subjected to external perturbations allows to develop efficient strategies of the active control. Indeed, active control of the plasmonic modes by applied dc fields [42][43][44][45][46] or charging [47][48][49][50] has been reported in the literature. In particular, if possible for metallic nanostructures 51,52 , the plasmon frequency change via electron doping as known in the THz range for semiconductor quantum wells or graphene [26][27][28][29][53][54][55] would allow active ultracompact devices in the visible range.…”