Plasmon-induced near-infrared fluorescence enhancement of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) emit near-infrared (NIR) fluorescence that is ideal for optical sensing. However, the low quantum yields diminish the sensor's signal-to-noise ratio and limits the penetration depths for in vivo measurements. In this study, we perform a systematic investigation of the plasmonic effects of Ag and Au nanoparticles of various geometries to tune and even enhance the fluorescence intensity of single-stranded DNA-wrapped SWCNTs (ssDNA-SWCNTs). We observe a chirality-dependent NIR fluorescence enhancement that varies with both nanoparticle shape and material, with Au nanorods increasing (7, 5) and (7, 6) chirality emissions by 80% and 60% and Ag nano triangles increasing (7, 5) and (6, 5) emissions by 200% and 240%, respectively. The chirality-dependent enhancement was modeled using finite element modeling (FEM), which confirms contributions not only from a plasmon-induced localized increase in electron density but also from the radiative recombination of dark exciton states from the resulting electromagnetic field. Finally, we demonstrate the application of these nanoparticles in enhancing the single-molecule fluorescence of individual SWCNTs imaged in a custom-built confocal setup. The plasmonically coupled sensors show four orders of magnitude greater sensitivity towards ferricyanide, a model analyte, compared to the non-coupled sensors. Plasmonic nanoparticles thus provide a tunable means of modulating SWCNT fluorescence to study fundamental transitions of otherwise forbidden states and to improve the optical sensing performance. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

In this study, the plasmonic effects of Ag and Au nanoparticles with different geometries on the fluorescence intensity of single-stranded DNA-wrapped single-walled carbon nanotubes (ssDNA-SWCNTs) were systematically investigated. Chirality-dependent fluorescence enhancement was observed, which varied with nanoparticle shape and material. Au nanorods increased the fluorescence of (7, 5) and (7, 6) chiralities by 80% and 60% respectively, while Ag nano triangles increased the fluorescence of (7, 5) and (6, 5) chiralities by 200% and 240% respectively. Finite element modeling confirmed contributions from a plasmon-induced localized increase in electron density and radiative recombination of dark exciton states from the resulting electromagnetic field.