From individual to collective chirality in metal nanoparticles

Abstract

Recent reports have illustrated the promising potential of chiral metal nanostructures, which exploit the characteristic localized surface plasmon resonance of metal colloids, to produce intense optical activity. In this article we review the concepts, synthetic methods, and theoretical predictions underlying the chirality of metal colloids with a particular emphasis on the size range of 10-100 nanometers. The formation of individual colloidal nanoparticles with a chiral morphology and a plasmonic response remains elusive; however, collective chirality and the associated optical activity in nanoparticle assemblies is a promising alternative that has seen a few recent experimental demonstrations. We conclude with a perspective on chiral nanostructures built up from achiral anisotropic metal particles.

Coating matters: the influence of coating materials on the optical properties of gold nanoparticles

“…Besides, Pd and Pt, Ni can be also be deposited onto Au nanorods, which confers them with magnetic properties, and for example they can be aligned in an external magnetic fi eld [214] . Controlled alignment of Au nanorods [80,215,216] , in particular with external magnetic fi elds could provide switchable optical and electronic systems (e.g., switch able colors or SERS hotspots) [217] , but coating the rods with Ni signifi cantly attenuates the longitudinal plasmon of Au nanorods. However, retention of the resonance of the Au cores is in principle possible by controlling the thickness of the Ni shells.…”

Emergence of collective dynamical chirality for achiral active particles

“…For instance, establishment of leftright asymmetry in embryonic development, one of the most intriguing biological phenomena, involves coordinated activity of many cells [15,16] where the ability of cells to distinguish between left and right is evident in systems of chiral patterns formed by collective motion of identical cells confined in circular island or ring/stripeshaped micropatterns [17][18][19][20]. On the other hand, CDC may also inspire new routines for fabrication of complex chiral architectures by dynamically self-assembling simple and achiral building blocks [21], e.g., chiral clusters of asymmetric colloidal dimers have been successfully assembled by using alternating current electric fields [22]. Revealing how CDC arises from groups of active units is then very important for the understanding of the formation mechanism.…”

Formation of chiral fields in a symmetric environment

“…This chiroptical far-field response is a consequence of geometrical chirality. In recent years, the concept of chirality has gathered substantial attention in the field of plasmonics [2][3][4][5][6][7]. Artificial geometrically chiral nanostructures with huge chiroptical farfield responses were reported in planar [8][9][10][11], bi-and multilayered [12][13][14][15][16][17][18][19][20][21], and even threedimensional geometries [22][23][24][25][26][27].…”