Site-selective functionalization of plasmonic nanopores for enhanced fluorescence emission rate and Förster resonance energy transfer

Abstract

In this work, we use a site-selective functionalization strategy to decorate plasmonic nanopores with one or more fluorescent dyes. Using an easy and robust fabrication method, we manage to build single plasmonic rings on top of dielectric nanotubes with different inner diameters. The modulation of the dimension of the nanopores allows us to both tailor their field confinement and their Purcell Factor in the visible spectral range. In order to investigate how the changes in geometry influence the fluorescence emission efficiency, thiol-conjugated dyes are anchored on the plasmonic ring, thus forming a functional nanopore. We study the lifetime of ATTO 520 and ATTO 590 attached in two different configurations: single dye, and FRET pair. For the single dye configuration, we observe that the lifetime of both single dyes decreases as the size of the nanopore is reduced.The smallest nanopores yield an experimental Purcell Factor of 6. For the FRET pair configuration, we measure two regimes. For large nanopore sizes, the FRET efficiency remains constant. Whereas for smaller sizes, the FRET efficiency increases from 30 up to 45% with a decrease of the nanopore size. These findings, which have been also supported by numerical simulations, may open new pathways to engineer the energy transfer in plasmonic nanopores with potential applications in photonics and biosensing, in particular in single-molecule detection towards sequencing.In recent years, plasmonic nanopores have been proposed for applications in single molecule detection towards sequencing 1 . Compared to the more common solid-state nanopores which are typically used for single molecule experiments based on ionic current measurements 2 , plasmonic nanopores offer interesting advantages for optical spectroscopic approaches 3,4,5 . Some of the key features of plasmonic nanopore are reduction of detection volume, localization of the electromagnetic field and increase of the signal-to-noise ratio. As a result, plasmonic nanopores find application in single molecule detection and sequencing based on Surface Enhanced Raman Scattering (SERS) 4 , as well as in fluorescence spectroscopy experiments 6,7 . In particular, enhanced fluorescence in plasmonic nanopores has been verified in single molecule DNA detection 8,3 . In these works, one or more nucleotides are

Bio‐Assisted Tailored Synthesis of Plasmonic Silver Nanorings and Site‐Selective Deposition on Graphene Arrays

“…To note, the lifetime measurements are not enough to claim that there is a fluorescence enhancement, as the fluorescence is the combination of absorption and emission. Anyway, lifetime reduction, as well as local field enhancement, is a typical effect of plasmonic structures . Thus, our measurements provide good evidence that plasmonic effects are present in the PRX‐AgNR structures.…”

“…Anyway, lifetime reduction, as well as local field enhancement, is a typical effect of plasmonic structures. [60] Thus, our measurements provide good evidence that plasmonic effects are present in the PRX-AgNR structures.…”

“…However, it is worth to note that two different dyes were used to acquire the images by confocal microscope (Alexa647) and for the EE measurements (ATTORho6G). The EE properties of the PRX‐AgNR structures were evaluated carrying out a comparative lifetime analysis . This method is independent from the number of emitting dyes and can be used to compare PRX and PRX‐AgNRs directly.…”

“…Each measurement was repeated several times, and the result was given as the average plus an uncertainty given by the standard deviation. More information on the optical setup can be looked up in our previous publication . ATTORho6G dyes (533–557 nm λ ex − λ em ) were used for the labeling.…”

“…The EE properties of the PRX-AgNR structures were evaluated carrying out a comparative lifetime analysis. [60] This method is independent from the number of emitting dyes and can be used to compare PRX and PRX-AgNRs directly. Using a home-made optical setup (see the Experimental Section), we computed the lifetime decay of the labeled PRX and the PRX-AgNR structures.…”