Plasmonic elliptical nanoholes for chiroptical analysis and enantioselective optical trapping

TL;DR

This paper introduces a simple, achiral elliptical nanohole platform in gold films that enables chiroptical analysis and enantioselective optical trapping of nanoparticles using linearly polarized light, with potential for low-noise chiral sensing.

Contribution

The study demonstrates a novel, easy-to-implement elliptical nanohole platform for chiroptical analysis and enantioselective trapping, reducing background noise compared to traditional methods.

Findings

Elliptical nanoholes generate localized chiral optical fields under linear polarization.

The platform can selectively trap or repel nanoparticles based on chirality.

Deeper trapping potential for plasmonic nanospheres reduces enantioselectivity.

Abstract

A simple yet effective achiral platform using elliptical nanoholes for chiroptical analysis is demonstrated. Under linearly polarized excitation, an elliptical nanohole in a thin gold film can generate a localized chiral optical field for chiroptical analysis and simultaneously serve as a near-field optical trap to capture dielectric and plasmonic nanospheres. In particular, the trapping potential is enantioselective for dielectric nanospheres, i.e., the hole traps or repels the dielectric nanoparticles depending on the sample chirality. For plasmonic nanospheres, the trapping potential well is much deeper than that for dielectric particles, rendering the enantioselectivity less pronounced. This platform is suitable for chiral analysis with nanoparticle-based solid-state extraction and pre-concentration. Compared to plasmonic chiroptical sensing using chiral structures or circularly polarized light, elliptical nanoholes are a simple and effective platform, which is expected to have a relatively low background because chiroptical noise from the structure or chiral species outside the nanohole is minimized. The usage of linearly polarized excitation also makes the platform easily compatible with a commercial optical microscope.