Decoupling absorption and emission processes in super-resolution localization of emitters in a plasmonic hotspot

David L Mack,Emiliano Cortés,Tyler Roschuk,Peter Török,Vincenzo Giannini,Stefan A Maier

doi:10.1038/ncomms14513

David L Mack, Emiliano Cortés + Show 4 more

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https://doi.org/10.1038/ncomms14513

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Journal: Nature Communications	Publication Date: Feb 17, 2017
Citations: 94	License type: open-access

Affiliation: Imperial College London

Abstract

The absorption process of an emitter close to a plasmonic antenna is enhanced due to strong local electromagnetic (EM) fields. The emission, if resonant with the plasmonic system, re-radiates to the far-field by coupling with the antenna via plasmonic states, whose presence increases the local density of states. Far-field collection of the emission of single molecules close to plasmonic antennas, therefore, provides mixed information of both the local EM field strength and the local density of states. Moreover, super-resolution localizations from these emission-coupled events do not report the real position of the molecules. Here we propose using a fluorescent molecule with a large Stokes shift in order to spectrally decouple the emission from the plasmonic system, leaving the absorption strongly resonant with the antenna’s enhanced EM fields. We demonstrate that this technique provides an effective way of mapping the EM field or the local density of states with nanometre spatial resolution.

Highlights

The absorption process of an emitter close to a plasmonic antenna is enhanced due to strong local electromagnetic (EM) fields
By forcing the majority of the molecules to be in temporary dark states[6], what would have been bright images composed of thousands of overlapping fluorescent point spread functions (PSF) that make up conventional fluorescence microscopy images, become sparse images where the individual PSF, corresponding to single molecules, are spatially separated
The molecules are transient on the surface of the sample, and for the low laser powers employed in this experiments the total number of collected photons in each single molecule event is limited by the absorption desorption time of the fluorescent molecules more than by their photobleaching

Summary

Introduction

The absorption process of an emitter close to a plasmonic antenna is enhanced due to strong local electromagnetic (EM) fields. We propose using a fluorescent molecule with a large Stokes shift in order to spectrally decouple the emission from the plasmonic system, leaving the absorption strongly resonant with the antenna’s enhanced EM fields We demonstrate that this technique provides an effective way of mapping the EM field or the local density of states with nanometre spatial resolution. Some other strategies aimed at nanostructure characterization have involved either using a single molecule fixed to the end of a probe as a constant source of illumination[16] or placing an optical antenna at a probe tip to map the directionality of the antenna’s emission when scanning fluorescent molecules[17] While these techniques have improved our ability to study fluorescence in plasmonic systems, they do not offer the ability to probe the far-field generated EM hotspots that are produced near plasmonic nanoantennas. For optimally field aligned dipole moments we arrive at: ð2Þ

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