SERS Orientational Imaging of Silver Nanoparticle Dimers

Abstract

This Article introduces surface-enhanced Raman scattering (SERS) orientational imaging as a powerful far-field optical technique for determining the in-plane and out-of-plane orientations of SERS-active nanoparticle dimers. Optical images of Rhodamine 6G (R6G) SERS emission patterns are measured and correlated with atomic force microscopy (AFM) images of the associated SERS-active silver nanoparticle dimers. The AFM is used to measure individual silver nanoparticle dimer orientations and height asymmetry, defining in-plane and out-of-plane angles associated with the dimer geometry. Theoretical emission pattern images based on these angles are generated using a simple dipole emission model and show excellent agreement with the experimental emission patterns. This technique provides a rapid all-optical technique to analyze the orientation of SERS active nanoparticle dimers.

Interfacial liquid-state surface-enhanced Raman spectroscopy

“…The merits of the Raman experiments in our study are twofold: it provides further experimental verification of the vertical orientation of GNRs at the interface, and is the first demonstration of the substrate-free interfacial liquid-state surface-enhanced Raman spectroscopy. In principle, the orientation of anisotropic gold nanoparticles (for example, dimers 18 and GNRs 28 ) can be indirectly resolved by Raman scattering experiments. In our experiment, GNRs with a longitudinal plasmon resonance of B785 nm were used ( Supplementary Fig.…”

“…Because of the anisotropic structure of the GNRs, two plasmon resonance bands are induced by the transverse and longitudinal oscillations of free electrons 29 . Note that the SERS intensities depend strongly on both the orientation of the GNRs and the illumination direction of the laser 18,28,30 . When the long axis of the GNRs is perpendicular to the illumination direction of the incident light, a resonance condition in a far-field regime is satisfied resulting in significant amplification of the Raman signal ( Fig.…”

“…O riented assemblies of functional colloidal nanoparticles [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] are important for both fundamental science and technological applications. Such assemblies have been realized on two-dimensional (2D) solid substrates by utilizing evaporation-based convection 6,7 , capillary interaction 8 , electric fields 9,10 , substrate templating 11,12 and surface tailoring of nanoparticles 13,14 .…”

Superlocalization Surface-Enhanced Raman Scattering Microscopy: Comparing Point Spread Function Models in the Ensemble and Single-Molecule Limits

“…The emission pattern is dominated by a bright central lobe, but there are low-intensity side lobes oriented parallel to the long axis of the dimer, indicative of dipolar behavior. 22,23,29,34 Fitting the emission pattern to the 2-D Gaussian in eq 1 ( Figure 2C), we find that this simple model fails to capture all of the features of the SERS emission pattern, particularly the low-intensity side lobes, as seen in the systematic error in the calculated residuals shown in Figure 2D.…”

Applying Super‐Resolution Imaging Techniques to Problems in Single‐Molecule SERS

“…If nanoparticle height information is required, AFM can also be used to correlate nanoparticle structure to optical activity. For this purpose, a combined AFM/total internal reflection optical microscope is used [36][37][38]. The optical microscopy system allows the user to locate the same area investigated in the super-resolution study, while the AFM gives sub-diffraction limited structural information on the nanoparticle aggregates.…”