Gap enhanced fluorescence as a road map for the detection of very weakly fluorescent emitters from visible to ultraviolet

Duncan Mcarthur,Francesco Papoff

doi:10.1038/s41598-017-14250-x

Abstract

We analyze the enhancement of the rates of both the emission and the far field radiation for dipoles placed in the gap between a metallic nanorod, or nanosphere, and a metallic substrate. For wavelengths between 150 nm and 650 nm, the response of the gapped nanostructures considered in this work is dominated by few principal modes of the nanoparticle, which include self-consistently the effect of the substrate. For wavelengths shorter than 370 nm, the far field radiative enhancements of aluminum nanostructures are significantly higher than those for gold or silver. With aluminum, bright mode resonances are tunable over tens or hundreds of nanometers by changing the size of the nanoparticle and have far field radiative enhancements of up to three orders of magnitude. These results provide a road map to label-free detection of many emitters too weakly fluorescent for present approaches.

Highlights

Nanostructures can induce large variations in many fundamental quantum phenomena such as the rate of spontaneous emission[1,2], the photonic Lamb shift of resonance frequencies and Casimir-Polder forces[3]
The emission rate affects the lifetime of the emitter, and the far field emission rate is proportional to the fraction of decay events detected in the far field, where fluorescence signals are detected in most experiments
We find that aluminum nanoparticles and substrates are ideally suited for label-free detection of weakly fluorescent molecules in the ultraviolet because they have resonances with a much stronger far field radiative enhancement than similar nanostructures of gold or silver for wavelengths shorter than 370 nm

Summary

Introduction

Nanostructures can induce large variations in many fundamental quantum phenomena such as the rate of spontaneous emission[1,2], the photonic Lamb shift of resonance frequencies and Casimir-Polder forces[3]. We find that aluminum nanoparticles and substrates are ideally suited for label-free detection of weakly fluorescent molecules in the ultraviolet because they have resonances with a much stronger far field radiative enhancement than similar nanostructures of gold or silver for wavelengths shorter than 370 nm. These resonances are tunable between 150 nm and 650 nm and can produce a simultaneous enhancement of the decay rates of dipolar emitters placed in the gap between the nanoparticle and the substrate, and of the radiation emitted in the far field. A more technical summary of the theory can be found in the methods section

Methods

Results

Conclusion