In Situ Observation of Unique Bianalyte Molecular Behaviors at the Gap of a Single Metal Nanodimer Structure via Electrochemical Surface-Enhanced Raman Scattering Measurements

Abstract

Electrochemical surface-enhanced Raman scattering measurements of a monomolecule layer have been performed using a single Au dimer structure with a well-defined gap distance. Through the bianalyte measurements under the electrochemical potential control, we have successfully observed the change in the adsorption states depending on the electrochemical potential at the surface of the Au structure. The time-dependent dynamics of the formation of the mixed bianalyte layer was clarified to form unique adsorbed states under excitation light illumination on the surface.

Electrochemical SERS on 2D Mapping for Metabolites Detection

“…Two mechanisms led to the enhancement: First, the charge transfer effect induced between metabolites and Fermi level of AuNPs probably led to the enhancement for all of the characteristic peaks of metabolites . Taking 6-TGNs as an example, in Figure a, we observed that not only was the characteristic peak at 1290 cm –1 (N1–C6 stretching mode) enhanced but also the characteristic peaks at 570 cm –1 (deformation vibration of the pyrimidine ring), 907 cm –1 (P–OH symmetric stretching mode), and 1367 cm –1 (C7–N8 stretching mode) were enhanced. The second mechanism was associated with the alignment of the metabolites, which led to the formation of Au–S bonds between AuNPs and 6-TGNs at 300 cm –1 .…”

Precise Control of Nanoscale Interface for Efficient Electrochemical Reactions

“…[55][56][57] To understand the molecular behavior strongly interacted with the plasmonic field at the well-defined nanostructure surface, we attempted to combine SERS measurements with the electrochemical potential control method. [58][59][60][61][62] As mentioned above, the electrochemical potential scan can easily change not only the molecular orientation via the surface charge but also the resonance effect. As one example, we have conducted electrochemical SERS measurements using bi-analyte solution containing 4'4-bipyride and 2'2-bipyride.…”

Room-Temperature Molecular Manipulation via Plasmonic Trapping at Electrified Interfaces

“…As the evaluation tool for plasmon-induced optical trapping, surface-enhanced Raman scattering (SERS) can be used to observe molecular condensations due to its high resolution. − In this article, we report the results on the observations of the suppression of the molecular diffusion and formation of the unique condensed phase within the plasmonic field immersed in the bianalyte aqueous solution of 4,4′-bipyridine (44bpy) and 2,2′-bipyridine (22bpy). In our previous study, we have observed the evolution of the resonant state of 44bpy depending on the molecule orientation, which is expected for the increment in the optical force. , To evaluate the molecular manipulations induced by the optical force at the plasmonic field, SERS measurements have been conducted under electrochemical potential control. The electrochemical method makes it possible to control not only the orientation of molecules adsorbed onto the metal surface but also the resonance state of molecules as we reported before .…”

“…LSPR is the collective oscillation of the free electrons in the metal nanostructures triggered by visible-light illumination. Thus, optical properties of metal nanostructures are precisely tuned by the control of their sizes, shapes, or metal species. , For example, the bowtie structure with the gap distance of less than 5 nm generates a relatively strong optical field (hot spot) at the gap. − Within such plasmonic fields, various unique photoresponse phenomena, e.g., the formation of the new hybridized state, the enhancement of Raman scattering, or efficient photochemical reactions, can be induced. − Our previous works have revealed that the selection rule of electronic excitation is modified by the strong localization of the light field, leading to the formation of novel excited states which are not produced by normal light illumination. − In addition, very recently, we have found that the unique molecular selective condensation was observed at the hot spots under the conditions of resonant electronic excitation at an electrified interface . This molecular condensation resulted from the improvement of the light–molecular interaction under resonant conditions.…”