Engineering Intrinsically Chiral Gold Nanostructures with Tailored Near-Infrared Optical Activity via a Multistep Growth Strategy

Inherently chiral nanoparticles attract tremendous interest as they unfold the mystery behind symmetry breaking, chiral amplification, and chiral transmission, processes key to understanding homochirality and the origin of life. In this context, the synthesis of discrete intrinsically chiral plasmonic nanoparticles with circular dichroism in the near-infrared region (NIR-CD) remains both a challenging and fascinating topic. Herein, we developed a facile method for synthesizing helicoidal nanorods (HNRs) with strong, stable CD with a comparatively narrow bandwidth in the near-infrared region using cysteine as a symmetry-breaking agent. Electron microscopy reveals that the optical activity stems from surface protrusions and edge tilting. By tuning the cysteine concentration and seed volume, the growth and morphology of these nanostructures can be precisely controlled. This allows for the fabrication of diverse chiral forms with tunable plasmonic responses. The research establishes a clear structure-property relationship linking morphology to optical performance. These intrinsically chiral plasmonic nanoparticles, with strong optical activity, open pathways for advanced applications in enantioselective catalysis, chiral biosensing, and spintronics.