Electrochemical Control of the Time-Dependent Intensity Fluctuations in Surface-Enhanced Raman Scattering (SERS)

Abstract

Time-dependent fluctuations in surface-enhanced Raman scattering (SERS) intensities were recorded from a roughened silver electrode immersed in diluted solutions of rhodamine 6G (R6G) and congo red (CR). These fluctuations were attributed to a small number of SERS-active molecules probing regions of extremely high electromagnetic field (hot spots) at the nanostructured surface. The time-dependent distribution of SERS intensities followed a tailed statistics at certain applied potentials, which has been linked to single-molecule dynamics. The shape of the distribution was reversibly tuned by the applied voltage. Mixtures of both dyes, R6G and CR, at low concentrations were also investigated. Since R6G is a cationic dye and CR is an anionic dye, the statistics of the SERS intensity distribution of either dye in a mixture were independently controlled by adjusting the applied potential. The potential-controlled distribution of SERS intensities was interpreted by considering the modulation of the surface coverage of the adsorbed dye by the interfacial electric field. This interpretation was supported by a two-dimensional Monte Carlo simulation that took into account the time evolution of the surface configuration of the adsorbed species and their probability to populate a hypothetical hot spot. The potential-controlled SERS dynamics reported here is a first step toward the spectroelectrochemical investigation of redox processes at the single-molecule level by SERS.

Unforeseen distance-dependent SERS spectroelectrochemistry from surface-tethered Nile Blue: the role of molecular orientation

“…The 588 cm −1 mode continues to decrease at potentials well positive of NB oxidation, which suggests that the electrode polarity is also influencing the orientation of the transition dipoles. 24 Moreover, when the solvatochromic NB intercalates into the hydrophobic SAM, we expect the absorption to shift to higher energies, resulting in a loss of resonance enhancement. [25][26][27] These effects most likely work in concert to generate a decrease in SERS intensity when the oxidized form of NB intercalates into the SAM on the electrode surface.…”

Advances in Plasmonic Technologies for Point of Care Applications

“…25 Single molecule detection has been achieved using SERS technology. 26 The method interrogates Raman shifts originating from molecular vibrational energy levels, and therefore, allowing to distinguish structurally similar molecules if they have distinct vibrational spectra. Experimentally, the utilization of fiber optics and optofluidics, along with the use of portable spectrometers, holds potential for future label-free POC applications.…”

Dependence of Plasmonic Properties on Electron Densities for Various Coupled Au Nanostructures

“…27 Monitoring the enhancement alteration is crucial especially to obtain the dynamic information on a single molecule in optical spectroscopy measurement. 23 Several reports have demonstrated the near field properties of a charged standalone nanostructure. 27−29 Using a Gersten−Nitzan model, the electromagnetic enhancement of an isolated nanostructure can be numerically calculated.…”