Super-resolution imaging of surface-enhanced Raman scattering hot spots under electrochemical control

Abstract

Super-resolution surface-enhanced Raman scattering (SERS) imaging is used to map out SERS hot spots in aggregated silver nanoparticles labeled with the electrochemically-active probe molecule Nile Blue. In super-resolution SERS, the diffraction-limited emission from a SERS-active nanoparticle aggregate is fit to a 2-dimensional Gaussian in order to localize the site of emission, or emission centroid, with 5-10 nm precision. This strategy typically involves working at or near the single molecule concentration level, in order to avoid the super-position of signals from multiple emitters, which leads to an ensemble-averaged centroid position and no spatial information about the location of individual emitters. We have proposed working above the single molecule concentration by using electrochemical control to transition the Nile Blue between its emissive (oxidized) and non-emissive (reduced) form, in order to spatially isolate individual Nile Blue molecules on the surface of aggregated silver nanoparticles. Using this electrochemical modulation strategy, SERS-active regions on nanoparticle aggregates can be mapped out by fitting the centroid location of the emitters as a function of applied potential. Interestingly, while the modulation of Nile Blue SERS intensity does not follow the expected on/off trend with applied potential, we find that we are still able to map out SERS hot spots even while working above the single molecule level.

Characterizing the Spatial Dependence of Redox Chemistry on Plasmonic Nanoparticle Electrodes Using Correlated Super-Resolution Surface-Enhanced Raman Scattering Imaging and Electron Microscopy

“…This trend is based on our qualitative overlay between the calculated centroid positions and the nanoparticle structure, yet we have sizable data from our previous work to validate the legitimacy of these assignments. 15,34,46 In all cases, the potential-dependent centroid positions track with specific structural features of the nanoparticles, indicating that this effect is not induced by local field gradients on the bulk ITO or changes in the nanoparticle structure with time. The former is substantiated by pairs of nanoparticle aggregates in which the centroid moves between two individual nanostructures showing that this is a nanoparticle-dependent (rather than substratedependent) effect, whereas the latter is further substantiated by localized surface plasmon resonance (LSPR) measurements showing that the Rayleigh scattering from the nanoparticles remains constant as the potential is scanned, indicating that we do not have changes in the nanoparticle aggregation pattern or local charging effects in these experiments (Figures S-9−S-14, Supporting Information).…”

Modeling super-resolution SERS using a T-matrix method to elucidate molecule-nanoparticle coupling and the origins of localization errors

“…Plasmonic hot spots in aggregates are often many orders of magnitude greater in intensity than single nanoparticles, so understanding super-resolution SERS for these structures is essential for experiments in single-molecule chemistry. 4,5 We think the method introduced here will be effective at predicting diffraction-limited images for the experiments using nanoparticle aggregates.…”

“…Super-resolution surface-enhanced Raman scattering (SERS) microscopy enables the spatial localization of plasmonic hot spots below the diffraction limit of light. [1][2][3][4][5] When irradiated with visible light, noble metal nanoparticles produce strong local electromagnetic fields due to plasmon resonances. [6][7][8] If a molecule is in the region of a strong electromagnetic field, or hot spot, the Raman signal of the molecule will be increased by many orders of magnitude.…”

WSe 2 -contact metal interface chemistry and band alignment under high vacuum and ultra high vacuum deposition conditions

“…2D materials, specifically transition metal dichalcogenides (TMDs, e.g. MoS 2 , WSe 2 ), with atomic scale thickness, tunable bandgap (~0.7-2.2 eV), and comparable mobilities with existing Si metal-oxidesemiconductor (MOS) channels, have emerged as strong candidates to complement current Si-based device technology [1,2]. TMDs are, in principle, ideal for the design of ultrashort channel field effect transistors (FETs) due to these novel properties which stem from their layered nature and set TMDs apart from Si, Ge, and III-V semiconductor materials.…”