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

Abstract

In this report, we compare the effectiveness of various dipole and Gaussian point spread function (PSF) models for fitting diffraction-limited surface-enhanced Raman scattering (SERS) emission images from rhodamine 6G-labeled nanoparticle dimers at both the high-concentration and single-molecule limit. Of all models tested, a 3-axis dipole PSF gives the best approximation to the experimental PSF, although none of the models utilized in the study were without systematic error when fitting the experimental data. In the high-concentration regime, all models localize the SERS emission to a stationary centroid position, with the dipole models providing additional orientation parameters that closely match the geometry of the dimer, indicating that the molecules are coupled to all resonant plasmon modes of the nanostructure. In the single-molecule case, the different models show a mobile SERS centroid, consistent with single-molecule motion on the surface, but the behavior of the centroid is model-dependent. Despite the centroid mobility in the single-molecule regime, the dipole PSF models still give accurate orientation information on the underlying dimer structure, although with less precision than the ensemble-averaged samples.

Spectrally Resolved Surface-Enhanced Raman Scattering Imaging Reveals Plasmon-Mediated Chemical Transformations

“…At the coverage of molecules used, the emission will localize to an intensity-weighted position representative of all the radiating molecules on the nanoparticle. 51 The intensity-weighted superposition may cause the super-resolved image ( Figure 5 A) to appear smaller than the particles in the TEM image.…”

Super-resolution imaging of SERS hot spots

“…4C and D). 32 In the case of the SM-SERS examples, variation in the centroid position and SERS intensity is observed as the single R6G molecule moves over the nanoparticle surface, changing how the molecular emission couples to the different plasmon modes of the dimer. On the other hand, in the MM-SERS case, the centroid position is extremely stable with a calculated precision of o0.5 nm in both cases.…”

“…5. 32 In addition to the centroid position (x 0d , y 0d ), the dipole model generates parameters associated with the 3-D orientation of the dipole emitter and the emission wavelength (among other values). The orientation values can be compared to the alignment of the longitudinal dipole axis based on the nanoparticle structure, while the emission wavelength can be compared to the SERS spectrum, providing a check of the appropriateness of the dipole model.…”

Localization accuracy of gold nanoparticles in single particle orientation and rotational tracking

“…Efforts have also been devoted to the search of optimal PSFs as the fitting model for accurate localization of emitting dipoles. For example, a threeaxis dipole PSF was found to best approximate the experimental PSF of a nanorod in Surface Enhanced Raman Scattering (SERS) microscopy [23].…”