Plasmonic Modes and Fluorescence Enhancement Coupling Mechanism: A Case with a Nanostructured Grating

Abstract

The recent development and technological improvement in dealing with plasmonic metasurfaces has triggered a series of interesting applications related to sensing challenges. Fluorescence has been one of the most studied tools within such a context. With this in mind, we used some well characterized structures supporting plasmonic resonances to study their influence on the emission efficiency of a fluorophore. An extended optical analysis and a complementary investigation through finite-difference time-domain (FDTD) simulations have been combined to understand the coupling mechanism between the excitation of plasmonic modes and the fluorescence absorption and emission processes. The results provide evidence of the spectral shape dependence of fluorescence on the plasmonic field distribution together with a further relationship connected with the enhancement of its signal. It has made evident that the spectral region characterized by the largest relative enhancement closely corresponds to the strongest signatures of the plasmonic modes, as described by both the optical measurements and the FDTD findings.

Refractive Index Dependence of Fluorescence Enhancement in a Nanostructured Plasmonic Grating

“…The following plasmonic field distributions and the corresponding shifts were also considered to confirm and strengthen the findings reported in [ 25 ]. The updated electric field expansions are also reported, proving the near-field capability in affecting the fluorescence reshaping.…”

“…The ATTO700 dye [ 27 ] was selected to provide a proper overlap with the plasmonic modes due to its emission spectrum spanning from 660 to 860 nm. The dye was drop-casted on the FS of the grating and on a bare SiO 2 glass slide for reference, following the procedure described in [ 25 ].…”

“…The sample was optically characterized with broadband (500 to 1110 nm) reflectance (R) and transmittance (T) measurements performed with a commercial Fourier transform spectrometer Bruker IFS66S coupled with a homemade micro reflectometer [ 25 ].…”

“…Thanks to the momentum conservation guaranteed by the periodicity of the metallic surface, surface plasmons can be directly excited and their signature can be detected in the R and T spectral features [ 25 , 30 ]. A Glan Taylor polarizer was used to select the TE or TM light polarization (electric or magnetic field perpendicular to the plane of incidence, respectively).…”

“…In a recent study [ 25 ], we analyzed the plasmonic modes and fluorescence enhancement coupling mechanism in relation to a plasmonic grating, proving that the fluorescence spectral shape depends on the plasmonic field distribution together with the enhancement of its signal. Additionally, the spectral region characterized by the most significative relative fluorescence enhancement is tightly linked to the most peculiar signatures of the plasmonic modes.…”