# Single‐Molecule Imaging and Spectroscopy Enables Quantification of Location‐Dependent Light–Matter Interactions on Nanoantennas

## TL;DR

This paper introduces a new method to study how the position of dye molecules on nanoantennas affects their light emission and spectral properties.

## Contribution

The novel approach combines correlative microspectroscopy and point-spread function analysis to quantify location-dependent light-matter interactions on nanoantennas.

## Key findings

- Fluorescence intensity and spectral shape are strongly influenced by the vertical position of dye molecules on gold nanocones.
- Site-specific deformations of the point spread function enable correlation of fluorophore positions with spectral features and binding rates.
- The method allows for multimodal quantification of spatial and spectral information in plasmonic systems.

## Abstract

Individual dye molecules coupled to a plasmonic nanoantenna have been established as a versatile foundation for single‐molecule studies. Crucial parameters such as fluorescence intensity enhancement, spectral properties, and emission patterns sensitively depend on the exact position of the dye molecule relative to the antenna and its hot spots. Knowledge about the binding location is therefore of paramount interest, however, it is highly challenging to obtain. We present a comprehensive approach based on correlative microspectroscopy of the optical properties of single fluorophores that transiently bind to gold nanocones using the DNA‐PAINT method. These 3D nanoantennas offer independently tunable in‐ and out‐of‐plane plasmon resonances with strong electric field enhancements at the tip apex and the nanocone base. We exploit site‐specific deformations of the point spread function in a high‐throughput approach as a means to correlate the position of the fluorophores on the nanoantenna surface to previously inaccessible parameters, investigating location‐specific binding probability, mode‐dependent spectral reshaping, and location‐resolved fluorescence enhancement factors. Our approach provides unprecedented multimodal quantification by correlating spatial and spectral information to open new avenues in fundamental studies of light–matter interactions and applications like biosensing.

The fluorescence intensity as well as the spectral shape of the emission of single dye molecules strongly depend on the molecules’ exact position relative to plasmonic nanoparticles in hybrid systems. By point‐spread function modification analysis, the vertical binding location of single fluorophores on gold nanocones is obtained and correlated to both spectral features and particle‐size dependent binding rates.© 2026 WILEY‐VCH GmbH