Fig. 2. Opposite handedness of three-dimensional plasmonic helicoids controlled by cysteine chirality transfer.31 (a) Circular dichroism spectra of chiral nanoparticles synthesized using l-Cys (black) and d-Cys (red). (b) SEM image of l-Cys nanoparticles. The highlighting in the insets illustrates the fact that the edges (solid lines) are tilted by an angle −ϕ with respect to the vertices (red dots) and cubic outline (dashed lines), as viewed along the [100] (left) and [111] (right) directions. (c) SEM image of d-Cys nanoparticles. The inset highlights the tilted edges (solid lines), cubic outline (dashed lines) and tilt angle (+ϕ). Mechanism of chirality evolution through the interplay between the enantioselective binding of molecules and the asymmetric growth of high-index facets. (d) Schematic of a stellated octahedron, differentiated by high-index facets consisting of [321]S, (S region, yellow) and [321]R (R region, purple) configurations. The vertices of the [111], [100] and [110] directions are indicated as A, B and C, respectively; A′ and B′ refer to the symmetric points of A and B, respectively. (e) Comparison of the atomic arrangement of the (321)R and (321̄)S gold surfaces for the region indicated by the red dotted box in a. The conformation at ‘kink’ sites is defined by the rotational direction of low-index microfacets in the sequence (111) → (100) → (110): clockwise, R region; anticlockwise, S region. (f) Polarization-resolved colors of light transmitted through seven different 432 helicoid III solutions with different λmax values (shown on the right) and an achiral nanoparticle solution (top row). The rotational angle of the analyzer was increased from −10° (left-most) to 10° (right-most) (see Methods). An angle of 0°, indicated by the dashed box, represents cross-polarized conditions. Adapted with permission from ref. 31. Copyright 2018 Springer Nature.
