Side-by-Side Assembly of Gold Nanorods Reduces Ensemble-Averaged SERS Intensity

Abstract

It is generally expected that aggregates of metal nanoparticles are more efficient surface-enhanced Raman scattering (SERS) probes than individual nanoparticles, due to the enhancement of the electric field in the interparticle gaps. We show that, for asymmetric nanoparticles, such as gold nanorods (NRs), this is not always the case: the plasmonic behavior of NRs depends on the mutual orientation of the NRs in the ensemble. We report the results of experimental studies and theoretical analysis of the optical properties of clusters of side-by-side assembled gold NRs. Ensembleaveraged SERS spectroscopy showed a reduction in SERS intensity. Comprehensive finite-difference time-domain simulations showed a reduction of electric field intensity as the number of NRs per cluster increased. This is due to destructive interference as the radial component of the surface plasmon modes of the NRs in the cluster interact with each other. The present work expands our understanding of the configuration-specific optical behavior of asymmetric gold nanoparticles. Furthermore, it offers guidance toward the "design rules" for the development of colloidal NR systems for sensing applications.

Gold Nanorods: Controlling Their Surface Chemistry and Complete Detoxification by a Two‐Step Place Exchange

“…This is known to originate from side-on aggregation, where end-on-end aggregation would cause a red-shift. [19,20] These observations cannot be explained by the increased viscosity or refractive index of the binary ethanol/water mixture, and we rule out any reshaping of the GNRs as an increase in the hydrodynamic radius is concurrently observed. One possible origin of this is the endfunctionalization with PEG, whereas the longitudinal side is, at least partially, coated with CTAB, observed by a number of other groups.…”

“…One possible origin of this is the endfunctionalization with PEG, whereas the longitudinal side is, at least partially, coated with CTAB, observed by a number of other groups. [20,21] The destabilization at intermediate con- Figure 2. Decrease in the stability of GNR-CTAB, measured by the broadening of the LSP absorbance upon addition of ethanol.…”

Biomimetic glycopolymers tethered gold nanoparticles: Preparation, self-assembly and lectin recognition properties

“…Thus, the modified amphiphilic glycopolymers may induce the hybrid nanoparticles to self-assemble into well-defined nanostructures such as micelles and vesicles with carbohydrate containing shell in aqueous solution. Furthermore, in some cases, the self-assembled hybrid nanoparticles coupled the electronic and optical properties of individual nanoparticles in their clusters, leading to new, interesting and potentially useful properties of the ensembles [28,29]. Therefore, the self-assembled Gly@Au NPs nanostructures may be served as catalytic reactors for chemical synthesis or targeted delivery vehicles for drugs with enhanced contrast imaging.…”

Trace cancer biomarker quantification using polystyrene-functionalized gold nanorods

“…By tuning the aspect ratio of AuNRs through minor modifications of the synthetic procedure, LSPR can be tuned to enhance coupling in the excitation/collection wavelength range [19]. The AuNR ends produce the highest electric field intensity [20,21], therefore analytes situated at the AuNR ends will experience the greatest Raman enhancement. A previous report used thiolated β-cyclodextrin (β-CD) as a binding pocket to capture analytes to the NR surface [22].…”