Chirality-Enabled Collective Alignment of Plasmonic Nanochains: All-Optical Control by an Unfocused Laser Beam

Optical alignment of anisotropic nanoparticles in a fluidic environment poses a significant challenge, often requiring complex light-field engineering to overcome disruptive Brownian motion. Here, we demonstrate a simple yet effective all-optical strategy to control the collective alignment of chiral plasmonic nanochains in bulk fluid using a single unfocused laser beam. This approach enables reversible optical switching between random and aligned states as well as between two different stable orientations of chiral nanochains within tens of seconds. This light-driven optical alignment is exclusive to chiral plasmonic nanochains and absent in achiral counterparts, revealing a previously unrecognized role for plasmonic chirality in optical manipulation. Theoretical simulations demonstrate that plasmonic chirality amplifies optical torques and interchain optical interactions, which facilitate and stabilize the collective alignment against Brownian disruption. With its chirality-specificity, simplicity, and scalability, this approach facilitates the development of optically reconfigurable chiral photonic systems and programmable micro/nanorobots.