Distance-Dependent Plasmon-Enhanced Fluorescence of Upconversion Nanoparticles using Polyelectrolyte Multilayers as Tunable Spacers

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted widespread interests in bioapplications due to their unique optical properties by converting near infrared excitation to visible emission. However, relatively low quantum yield prompts a need for developing methods for fluorescence enhancement. Plasmon nanostructures are known to efficiently enhance fluorescence of the surrounding fluorophores by acting as nanoantennae to focus electric field into nano-volume. Here, we reported a novel plasmon-enhanced fluorescence system in which the distance between UCNPs and nanoantennae (gold nanorods, AuNRs) was precisely tuned by using layer-by-layer assembled polyelectrolyte multilayers as spacers. By modulating the aspect ratio of AuNRs, localized surface plasmon resonance (LSPR) wavelength at 980 nm was obtained, matching the native excitation of UCNPs resulting in maximum enhancement of 22.6-fold with 8 nm spacer thickness. These findings provide a unique platform for exploring hybrid nanostructures composed of UCNPs and plasmonic nanostructures in bioimaging applications.

Recent Progress on Plasmon-Enhanced Fluorescence

“…Recently, polyelectrolyte (PC) layers acting as a spacer to precisely control the distance between UCNPs and AuNPs was presented. At the best resonance condition between the UCNPs and AuNPs, a maximum fluorescence enhancement as high as 22.6-fold was obtained [119]. Compared with the conventional works reported about the UC, which are based on depositing nanocrystals on noble metallic nanostructure with various shaped aforementioned, Schietinger et al presented the controlled PEF characteristic of UCNP (NaYF 4 :Er 3+ )…”

Effect of surface roughness on metal enhanced fluorescence in planar substrates and optical fibers

“…Nanostructured metal films and nanoparticles have been extensively studied for MEF [10][11][12][13][14][15][16]. The enhancement factors depend on the type, shape, size, and separation between nanoparticles, and enhancement values from 10 to 10 6 have been reported for some configurations.…”

“…Silver films of thicknesses around 50 nm with varying roughness from 2 nm to 8 nm were prepared by two methods, thermal vapor deposition and chemical electroless plating. As the plasmonic enhancement of fluorescence depends on the separation between the fluorophore and the metal [2][3][4]7,11], the optimal distance that provides maximum enhancement at a given roughness was achieved through layer-by-layer deposition of a polyelectrolyte multilayer spacer. Fluorescence intensity was found to increase for coatings with higher surface roughness.…”

Au nanoparticle@silica@europium coordination polymer nanocomposites for enhanced fluorescence and more sensitive monitoring reactive oxygen species

“…These enhanced regions can also change the local electromagnetic field density [29], and the enhancement of fluorescence emission depends on the competition of the distancedependent mechanism [17,30]. However, at the same time, it will also create faster radiation decays [31][32][33].…”

“…Fluorescence quenching also occurs by non-radiation energy transfer if the chromophore is situated in vicinity of Au NPs. The enhancing and quenching effects strongly depend on the distance between the surface of Au NPs and chromophores [15][16][17][18][19][20]. In the present work, we prepared Au NP@silica@eur-opium coordination polymers denoted as Au NP (Au NP) @SiO 2 @TDA-Eu nanocomposites by two steps: first, Au NP@SiO 2 nanaocomposites were prepared by a modified one-pot process [21,22].…”