Fingers Crossed: Optical Activity of a Chiral Dimer of Plasmonic Nanorods

Auguié, Baptiste; Alonso‐Gómez, José Lorenzo; Guerrero‐Martínez, Andrés; Liz‐Marzán, Luis M.

doi:10.1021/jz200279x

Cited by 221 publications

(246 citation statements)

References 44 publications

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“…32 The twisted AuNR dimer system has been investigated theoretically before using a coupled dipole theory. 12 We have applied full-wave electromagnetic simulations using the FDTD method and approximating the AuNRs as cylinders capped with hemispheres instead of ellipsoids, and have obtained similar results in the limit of large interrod distances. However, for small AuNR separations of a few nm as is the case in the experiments discussed below, fullwave electromagnetic simulations are necessary to correctly describe this system ( Figure S2).…”

Section: Resultsmentioning

confidence: 81%

“…11 Energy conservation requires that the overall integrated extinction CD spectrum is zero. 12 However, such energy conservation does not apply when absorption and scattering signal are measured separately. 12,13 This distinction between scattering and absorption vs. their sum, i.e.…”

Section: Toc Graphicmentioning

confidence: 99%

“…For molecular CD spectroscopy, it has been theoretically proven that the integrated CD signal is zero as a result of energy conservation. 11,12,52 The fact that only one band is observed in the CDS spectra ( Figure 2d) does not imply that this sum rule breaks down though. When the CD signal of the total attenuated energy -the sum of absorption and scattering -is considered for the AuNR dimer, we find that 13 However, little attention has been paid to this effect for chiral plasmonic nanostructures, mostly because ensemble CD spectra measure generally the extinction.…”

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confidence: 93%

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Circular Differential Scattering of Single Chiral Self-Assembled Gold Nanorod Dimers

Wang¹,

Smith²,

et al. 2015

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Circular dichroism spectroscopy is essential for structural characterization of proteins and chiral nanomaterials. Chiral structures from plasmonic materials have extraordinary strong circular dichroism effects compared to their molecular counterparts. While being extensively investigated, the comprehensive account of circular dichroism effects consistent with other plasmonic phenomena is still missing. Here we investigated the circular differential scattering of a simple chiral plasmonic system, a twisted side-by-side Au nanorod dimer, using single-particle circular dichroism spectroscopy complimented with electromagnetic simulations. This approach enabled us to quantify the effects of structural symmetry breaking, namely, size-mismatch between the constituent Au nanorods and large twist angles on the resulting circular differential scattering spectrum. Our results demonstrate that, if only scattering is considered as measured by dark-field spectroscopy, a homodimer of Au nanorods with similar sizes produces a circular differential scattering line shape that is different from the bisignate response of the corresponding conventional CD spectrum, which measures extinction, that is, the sum of scattering and absorption. On the other hand, symmetry breaking in a heterodimer with Au nanorods with different sizes yields a bisignate circular differential scattering line shape. In addition, we provide a general method for correcting linear dichroism artifacts arising from slightly elliptically polarized light in a typical dark-field microscope, as is necessary especially when measuring highly anisotropic nanostructures, such as side-by-side nanorods. This work lays the foundation for understanding absorption and scattering contributions to the CD line shape of single chiroplasmonic nanostructures free from ensemble-averaging, especially important for self-assembled chiral nanostructures that usually exist as both enantiomers.

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Section: Resultsmentioning

confidence: 81%

Section: Toc Graphicmentioning

confidence: 99%

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confidence: 93%

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Circular Differential Scattering of Single Chiral Self-Assembled Gold Nanorod Dimers

Wang¹,

Smith²,

et al. 2015

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“…Owing to close proximity, the excited plasmons in the two AuNRs can be strongly coupled 18 . The two crossed AuNRs constitute a 3D plasmonic chiral object [19][20][21][22] , which generates a theme of handedness when interacting with left-and right-handed circularly polarized light, giving rise to strong CD. …”

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confidence: 99%

Reconfigurable 3D plasmonic metamolecules

et al. 2014

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A reconfigurable plasmonic nanosystem combines an active plasmonic structure with a regulated physical or chemical control input. There have been considerable e orts on integration of plasmonic nanostructures with active platforms using topdown techniques. The active media include phase-transition materials, graphene, liquid crystals and carrier-modulated semiconductors, which can respond to thermal 1 , electrical 2 and optical stimuli 3-5 . However, these plasmonic nanostructures are often restricted to two-dimensional substrates, showing desired optical response only along specific excitation directions. Alternatively, bottom-up techniques o er a new pathway to impart reconfigurability and functionality to passive systems. In particular, DNA has proven to be one of the most versatile and robust building blocks 6-9 for construction of complex three-dimensional architectures with high fidelity 10-14 . Here we show the creation of reconfigurable three-dimensional plasmonic metamolecules, which execute DNA-regulated conformational changes at the nanoscale. DNA serves as both a construction material to organize plasmonic nanoparticles in three dimensions, as well as fuel for driving the metamolecules to distinct conformational states. Simultaneously, the threedimensional plasmonic metamolecules can work as optical reporters, which transduce their conformational changes in situ into circular dichroism changes in the visible wavelength range.Circular dichroism (CD), that is, differential absorption of left-and right-handed circularly polarized light, of natural chiral macromolecules is highly sensitive to their three-dimensional (3D) conformations 15 . Taking a similar strategy, we create 3D reconfigurable plasmonic chiral metamolecules 4,16 , whose conformation changes are highly correlated with their pronounced and distinct CD spectral changes in the visible wavelength range. Figure 1a shows the design schematic. Two gold nanorods (AuNRs) are hosted on a reconfigurable DNA origami template 7,10 , which consists of two 14-helix bundles (80 nm × 16 nm × 8 nm) folded from a long single-stranded DNA (ssDNA) scaffold with the help of hundreds of staple strands 13 . The two origami bundles are linked together by the scaffold strand passing twice between them at one point. To ensure the mobility of the DNA bundles and avoid the formation of a Holliday junction 17 , 8 unpaired bases are introduced to each ssDNA connector (Supplementary Note 1). Twelve binding sites are extended from each origami bundle for robust assembly of one AuNR (38 nm × 10 nm) functionalized with complementary DNA (Supplementary Note 2). The surface to surface distance of the two AuNRs is roughly 25 nm. Owing to close proximity, the excited plasmons in the two AuNRs can be strongly coupled 18 . The two crossed AuNRs constitute a 3D plasmonic chiral object [19][20][21][22] , which generates a theme of handedness when interacting with left-and right-handed circularly polarized light, giving rise to strong CD. Left-handedRight-handed Two gold nanorods (...

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“…The strong optical activity of the metal NP assemblies derives from the plasmonic interactions between nonchiral NPs arranged in a chiral geometry or the coulomb interactions between the NPs and the linked chiral molecules [5][6][7][8][9][10]. With the advance in both synthetic strategies and theoretical modeling, many chiral metal NP structures have been studied [11][12][13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Plasmonic Circular Dichroism of the Helical Nanosphere Assemblies and the Helical Nanoellipsoid Assemblies

Wang

Deng

2014

Plasmonics

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We investigate the circular dichroism (CD) of both the helical gold nanosphere assemblies and the helical gold nanoellipsoid assemblies by means of the discrete dipole approximation (DDA). For the helical gold nanosphere assemblies, we find that, with increasing the number of the nanospheres within a helical pitch, the CD spectra of the assemblies are red-shifted and the intensity of the CD signals is strengthened. We also investigate the E-field distributions of the helical nanosphere assemblies. The results show that the strong CD response of the nanosphere assemblies can be ascribed to the collective dipole and multipole interactions between nanoparticles. The CD signals of the solid helical structure exhibit periodical behaviors in half pitch, which is quite different from that of the nanosphere assemblies. The helical nanoellipsoid assemblies exhibit complicated plasmon-induced CD signals at the localized surface plasmon resonance (LSPR) frequency. The strength and wavelength of the CD signals can be manipulated in the range of 525 to 688 nm via tuning the aspect ratio of the nanoellipsoids. These results are important for designing the chiral plasmonic nanostructures with strong and tailorable optical properties.

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Fingers Crossed: Optical Activity of a Chiral Dimer of Plasmonic Nanorods

Cited by 221 publications

References 44 publications

Circular Differential Scattering of Single Chiral Self-Assembled Gold Nanorod Dimers

Circular Differential Scattering of Single Chiral Self-Assembled Gold Nanorod Dimers

Reconfigurable 3D plasmonic metamolecules

Plasmonic Circular Dichroism of the Helical Nanosphere Assemblies and the Helical Nanoellipsoid Assemblies

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