Gold nanoshell coated NaYF4nanoparticles for simultaneously enhanced upconversion fluorescence and darkfield imaging

Abstract

Lanthanide-doped upconversion nanocrystals (UCN) converting low energy photons to high energy photons have emerged as an efficient and versatile bioimaging and therapeutic tool. However, the upconversion efficiency of the UCNs is low, which limits their applications. Plasmonic modulation makes it possible to enhance the luminescence of these nanocrystals. We hypothesize that the enhancement of the upconversion luminescence for all the emission peaks simultaneously could be achieved if the UCNs are coated with a gold nanoshell and the surface plasmon resonance (SPR) peak is tuned to the near-infrared (NIR) region and made resonant with the absorption of the UCNs, thereby substantially increasing the excitation flux via local field enhancement (LFE) effect. Furthermore, the nanoparticles could be used for darkfield imaging due to the light scattering caused by the gold nanoshell. Herein, we report a poly-(amino acid)-templated gold-shell encapsulation of the silica coated NaYF 4 :Yb,Er UCNs and show how a deft tuning of the SPR peak from visible to NIR region dramatically transforms the luminescence quenching into an enhancement effect and how the nanoparticles are used for combined upconversion fluorescence and darkfield light scattering imaging.

Synthesis, Characterization, and Application of Core–Shell Co0.16Fe2.84O4@NaYF4(Yb, Er) and Fe3O4@NaYF4(Yb, Tm) Nanoparticle as Trimodal (MRI, PET/SPECT, and Optical) Imaging Agents

“…16,23,40,41 In order to incorporate this type of optical activity into our multimodality contrast NPs, lanthanide cations Er or Tm (active cations) were codoped with Yb 3+ (sensitizer) into the NaYF 4 layer. Up-conversion fluorescent emission was then observed under excitation with a 980 nm laser.…”

Advances of Upconversion Nanoparticles for Molecular Imaging

“…In addition, unselectively enhanced multicolour UC emissions and low pumping threshold were achieved in Au@β-NaYF 4 :Yb,Tm hybrid nanostructures. Zhang et al [44] reported a poly-(aminoacid)-templated gold-shell encapsulation of the silica coatedNaYF 4 :Yb,Er UCNPs, showing how a deft tuning of SPR peak from visible to NIR region dramatically transformed the luminescence quenching into an enhancement effect and how theNPs were used for combined UC fluorescence and dark field light scattering imaging. At one time, most commercially available two-photon fluorophoresare organic dyes that exhibit relatively low two-photon absorption crosssections, fluorescence quantum yield and photochemicalinstability (photobleaching).…”

Upconversion Nanoparticle-Based Nanocomposites

“…In this procedure, the size of the Ag nanoparticles, SiO 2 thickness, and the thickness of the upconversion layer can be controlled by changing the reaction parameters. Priyam et al [151] also developed a strategy in which the NaYF 4 :Yb,Er upconversion nanoparticles are first coated with silica and then a continuous gold nanoshell is grown via a poly(amino acid)-templated approach. The poly(amino acid), poly-L-histidine (PLH), is positively charged at neutral pH and electrostatically adsorbed onto the negatively charged silica-coated NaYF 4 :Yb,Er upconversion nanoparticles.…”

“…(ii) Metallic nanoparticles are attached or self-assembled onto the surface of lanthanide-doped fluoride, oxide, or vanadate upconversion nanoparticles [147,148,152,[158][159][160][161]. (iii) core/shell structures of metallic/silica/UCNPs, UCNPs/ silica/metallic, metallic/UCNPs, and UCNPs/metallic [150,151,162,163].…”