Plasmon-Mediated Chiroptical Second Harmonic Generation from Seemingly Achiral Gold Nanorods

Area of Science:

• Nanophotonics and Plasmonics
• Chiroptics
• Materials Science

Background:

• Chirality is a fundamental property in nature, governing interactions with polarized light.
• Achiral materials typically do not exhibit chiroptical responses.
• Gold nanorods offer tunable plasmonic properties.

Purpose of the Study:

• To demonstrate and characterize chiroptical signals from seemingly achiral gold nanorods.
• To investigate the role of nanorod shape and plasmon resonance in generating chiroptical effects.
• To establish a platform for chiroptical transduction using scalable nanostructures.

Main Methods:

• Synthesis of gold nanorods with specific shape anisotropy.
• Second harmonic generation (SHG) measurements.
• Polarization-resolved spectroscopy to analyze chiroptical signals.
• Plasmon-resonant excitation at specific wavelengths.

Main Results:

• Observed intrinsic chiroptical signals from achiral gold nanorods without chiral ligands.
• Demonstrated that atomic-level faceting and rounding induce linear-to-circular polarization modulation.
• Showed that plasmon-resonant excitation significantly amplifies the circularly polarized harmonic signals.
• Correlated the nanorod's structure-dependent susceptibility and plasmon field with its second-order polarizability.

Conclusions:

• Achiral gold nanorods can exhibit significant chiroptical responses driven by their intrinsic shape.
• Plasmon-plasmon coupling enhances the sensitivity of chiroptical detection.
• These nanorods provide a scalable, assembly-free platform for sensitive chiroptical transduction and sensing applications.