Four in One: Parallel Determination of Optical Activity and Optical Anisotropy from Single Plasmonic Nanostructures

Area of Science:

• Plasmonics
• Nanotechnology
• Optical Physics

Background:

• Chiral plasmonic nanostructures exhibit unique interactions with polarized light.
• Ensemble measurements obscure individual nanoparticle heterogeneity.
• Existing single-particle methods struggle to disentangle complex chiroptical signals.

Purpose of the Study:

• To develop a method for individually measuring linear/circular dichroism and birefringence in gold nanostructures.
• To correlate specific structural features with chiroptical responses at the single-particle level.
• To address limitations in current scattering-based chiroptical characterization techniques.

Main Methods:

• Utilized polarization-resolved calcite-assisted localization and kinetics microscopy.
• Swept linearly polarized excitation azimuth from 0° to 180°.
• Monitored changes in ellipticity and polarization azimuth of scattered light from individual nanostructures.

Main Results:

• Successfully differentiated linear/circular dichroism and linear/circular birefringence in individual gold nanostructures.
• Demonstrated that optical anisotropy (linear dichroism/birefringence) is wavelength-dependent, even in quasi-isotropic structures.
• Showed that substrate refractive index significantly impacts measured ellipticity, requiring careful consideration.

Conclusions:

• The developed technique provides a high-throughput, information-rich method for screening individual nanostructure chiroptical properties.
• Accurate characterization requires accounting for both circular and linear optical contributions and substrate effects.
• This approach enables a deeper understanding of structure-property relationships in chiral plasmonics.