Chiral and Achiral Nanodumbbell Dimers: The Effect of Geometry on Plasmonic Properties

Abstract

Metal nanoparticles with a dumbbell-like geometry have plasmonic properties similar to those of their nanorod counterparts, but the unique steric constraints induced by their enlarged tips result in distinct geometries when self-assembled. Here, we investigate gold dumbbells that are assembled into dimers within polymeric micelles. A single-particle approach with correlated scanning electron microscopy and dark-field scattering spectroscopy reveals the effects of dimer geometry variation on the scattering properties. The dimers are prepared using exclusively achiral reagents, and the resulting dimer solution produces no detectable ensemble circular dichroism response. However, single-particle circular differential scattering measurements uncover that this dimer sample is a racemic mixture of individual nanostructures with significant positive and negative chiroptical signals. These measurements are complemented with detailed simulations that confirm the influence of various symmetry elements on the overall peak resonance energy, spectral line shape, and circular differential scattering response. This work expands the current understanding of the influence self-assembled geometries have on plasmonic properties, particularly with regard to chiral and/or racemic samples which may have significant optical activity that may be overlooked when using exclusively ensemble characterization techniques.

All-optical reconfigurable chiral meta-molecules

“…It is worth noting that all these chiral metamolecules show high g-factors between 0.2 and 0.4 ( Supplementary Fig. 11), which is among the highest values in the reported chiral structures [17,18,24,[49][50][51][52].…”

Chiral 432 Helicoid II Nanoparticle Synthesized with Glutathione and Poly(T)20 Nucleotide

“…Especially in the field of plasmonics, strong chiral light‐matter interaction has been one of the fundamental needs with its wide potential application in chiral recognition sensing, optical metamaterials, enantioselective catalysis, and opto‐tele communication technologies . In this sense, relentless efforts have been dedicated to the construction of chiral plasmonic nanostructures using E‐beam lithography, direct laser writing, and macromolecular assembly . Despite sophisticated control of chiral nanostructures, state of the art technologies require complicated synthetic processes and have limitations on constructible morphologies.…”

“…[1][2][3][4][5][6][7][8][9] In this sense, relentless efforts have been dedicated to the construction of chiral plasmonic nanostructures using E-beam lithography, [10][11][12] direct laser writing, [13,14] and macromolecular assembly. [15][16][17][18][19][20] Despite sophisticated control of chiral nanostructures, state of the art technologies require complicated synthetic processes and have limitations on constructible morphologies. Therefore, facile synthesis methods to precisely control chirality on nanoscale remains a scientific and engineering challenge.…”

Composite Polymer Colloids for SERS‐Based Applications

“…This encapsulation method results in organized clusters when using spherical AuNPs, with a structure of concentric layers (Figure ‐A.2) . Encapsulation of anisotropic particles such as dumbbells allows formation of cross‐like assemblies, which display circular dichroism related to plasmonic chirality . From the perspective of SERS, this may however not be the ideal system, as polymer encapsulation may hinder molecular access to the AuNP surface, and encapsulated particles are well separated from each other, which hinders hot spot formation.…”