Chiral plasmonics

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Science Advances  17 May 2017:
Vol. 3, no. 5, e1602735
DOI: 10.1126/sciadv.1602735


  • Fig. 1 Solid plasmonic chiral structures.

    All these structures are intrinsically chiral, meaning they are all made of solid metal and exhibit a distinct handedness due to their shape. (A) Simulated transmittance spectra and plasmonic modes of a metallic spiral with two pitches. The structures basically block LCP light while transmitting RCP light nearly without loss. The observed plasmonic modes extend over the entire structure, thus being strongly handed themselves. (B) Tapered gold helices. In manipulating pitch and diameter of the spirals, the plasmonic modes can be manipulated, and an even larger operational wavelength band can be generated. (C) Nested plasmonic helices fabricated via stimulated-emission-depletion direct laser lithography. (D) Scanning electron microscopy image of plasmonic spirals fabricated via colloidal nanohole lithography. Being at the boundary of top-down and bottom-up techniques, this lithography technique allows for large-area fabrication. (E) Glancing angle deposition allows for the fabrication of extremely small solid gold spirals exhibiting a strong CD response in the visible wavelength range, with excellent mirror symmetry of the CD spectra of the two enantiomers, as expected from theory. a.u., arbitrary units. (F) Free-standing metallic spirals fabricated by electron beam–induced deposition, which allows for the direct writing of functional nanostructures. (G) A two-step lithography process allows fabricating on-edge solid metallic L-shapes, which show a strong chiral optical response. Figures were reproduced with permission from Gansel et al. (13) (A), Gansel et al. (14) (B), Kaschke and Wegener (18) (C), Frank et al. (20) (D), Mark et al. (22) (E), Esposito et al. (26) (F), and Dietrich et al. (30) (G).

  • Fig. 2 Chiral assemblies of achiral and chiral building blocks.

    (A) Two bars stacked on top of each other can be viewed as a fundamental chiral building block and as an analogy to the well-known Born-Kuhn model. (B) The assembly supports two modes, which, if ideally tuned, lead to a single dispersive lineshape in the CD spectrum. The ORD spectrum can be calculated from the CD spectrum because they are Kramers-Kronig–related. (C) Two-layered chiral structures composed of two individual 2D chiral gammadion shapes. (D) Stacked and twisted split-ring resonators arranged in a C4 symmetric lattice to render the eigenmodes of the system truly chiral. (E) Twisted stacked crosses. (F) Assemblies of achiral nanoparticles can be rendered handed due to configuration or constitution. (G) Illustration of constitutional chirality: Four particles of different height (as can be seen due to their different brightness) in an achiral arrangement generate a handed system. Figures were reproduced with permission from Yin et al. (42) (A and B), Zhao et al. (45) (C), Decker et al. (46) (D), Decker et al. (48) (E), Hentschel et al. (53) (F), and Ogier et al. (54) (G).

  • Fig. 3 Chiral plasmonic structures assembled on scaffolds.

    (A) TEM image of twisted anthraquinone-based oxalamide fibers, which are infiltrated with gold nanorods. (B) CD spectra of double helix assembled using peptides. The structure is illustrated with the help of 3D surface renderings of topographic volumes. (C) A system of layered twisted cellulose nanocrystals is used as a scaffold for gold nanorods. Figures were reproduced with permission from Guerrero-Martínez et al. (55) (A), Song et al. (56) (B), and Querejeta-Fernández et al. (59) (C).

  • Fig. 4 Chiral plasmonic structures assembled with the help of DNA strands and DNA origami.

    (A) A DNA backbone with helically attached binding sites is used to create helices of gold nanoparticles exhibiting a CD response around 550 nm. (B) Overgrowth of the particles with silver leads to an increased coupling strength, a much stronger CD response, and a small spectral red shift due to the increased coupling. (C) Gold nanoparticles are arranged in two parallel rows on a DNA origami and subsequently rolled up to form a spiral. (D) Using the possibility to differently facilitate the two sites of a DNA origami sheet, a handed rod dimer can be assembled. (E) Origami sheets are used to create stacks of rotated gold nanorods. The individual sheets are dressed with capture strands on both sides and by adding gold nanorods, which are dressed with complementary ssDNA to the formation of nanorod stacks. (F) Using specifically designed ssDNA nanoparticle pyramids constructed from two differently sized gold nanoparticles, a silver nanoparticle and a quantum dot can be assembled. (G) An origami sheet with four docking sites: three along an L-shape on the one interface and one on the other (which is used to assemble a chiral quadrumer). The handedness depends on the position of the fourth particle relative to the L-shape. The structures show a strong CD response. Figures were reproduced with permission from Kuzyk et al. (60) (A and B), Shen et al. (61) (C), Shen et al. (62) (D), Lan et al. (64) (E), Yan et al. (67) (F), and Shen et al. (69) (G).

  • Fig. 5 Switchable chiral plasmonic structures.

    (A) Top-down fabricated 3D molecule consisting of two individual chiral units, which together define the optical response of the entire system. The incorporation of silicon pads (green) allows researchers to optically address the chiral units and to manipulate their relative contribution to the overall response. (B) Two chiral units, one active chiral dimer (bottom) and one bias dimer (top), generate the overall chiral optical response, whereas one of them can be actively detuned with the help of the GST-326 layer, leading to a pronounced sign change in the optical response. (C) Switchable hybrid chiral plasmonic system, consisting of gold and magnesium nanoparticles in a ratchet wheel-like arrangement. Switching the magnesium plasmon off, via hydration, switches the chiral plasmonic response off. (D) Interlocked DNA bundles are dressed with two gold nanorods. The locks can be unlocked with the help of specifically designed DNA strands, followed by the formation of new DNA bonds that lock the two bundles with the opposite twisting angle, thus inverting the handedness and the chiral optical response. (E) Schematic illustration of DNA nanowalker. The lower red rod is static, whereas the upper yellow one can walk over the origami sheet and successively switch the chirality of the system. Figures were reproduced with permission from Zhang et al. (71) (A), Yin et al. (72) (B), Duan et al. (73) (C), Kuzyk et al. (75) (D), and Zhou et al. (77) (E).

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