Polymer-Coated NaYF₄:Yb³⁺, Er³⁺ Upconversion Nanoparticles for Charge-Dependent Cellular Imaging

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) are considered promising novel near-infrared (NIR) bioimaging agents with the characteristics of high contrast and high penetration depth. However, the interactions between charged UCNPs and mammalian cells have not been thoroughly studied, and the corresponding intracellular uptake pathways remain unclear. Herein, our research work involved the use of a hydrothermal method to synthesize polyvinylpyrrolidone-coated UCNPs (UCNP-PVP), and then a ligand exchange reaction was performed on UCNP-PVP, with the help of polyethylenimine (PEI) and poly(acrylic acid) (PAA), to generate UCNP-PEI and UCNP-PAA. These polymer-coated UCNPs demonstrated good dispersibility in aqueous medium, had the same elemental composition and crystal phase, shared similar TEM and dynamic light scattering (DLS) size distribution, and exhibited similar upconversion luminescence efficiency. However, the positively charged UCNP-PEI evinced greatly enhanced cellular uptake in comparison with its neutral or negative counterparts, as shown by multiphoton confocal microscopy and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Meanwhile, we found that cationic UCNP-PEI can be effectively internalized mainly through the clathrin endocytic mechanism, as revealed by colocalization, chemical, and genetic inhibitor studies. This study elucidates the role of the surface polymer coatings in governing UCNP-cell interactions, and it is the first report on the endocytic mechanism of positively charged lanthanide-doped UCNPs. Furthermore, this study provides important guidance for the development of UCNPs as specific intracellular nanoprobes, allowing us to control the UCNP-cell interactions by tuning surface properties.

Upconversion of Rare Earth Nanomaterials

“…Various in vitro (98)(99)(100)(101) and in vivo (102-106) models have been employed to validate the bioimaging potentials of RE UCNs. For example, Li and coworkers (103) synthesized sub-10-nm β-NaLuF 4 :Gd,Yb,Tm UCNs for sensitive in vivo imaging.…”

Photonen aufkonvertierende Nanopartikel zur optischen Codierung und zum Multiplexing von Zellen, Biomolekülen und Mikrosphären

“…[176] Auf diese Weise codierte Zellen kçnnen auch in Tiere injiziert werden, um deren zelluläre Dynamik über die Zeit zu verfolgen. Die Gruppe von Wang [177] dotierte aufkonvertierende Nanostäbchen des Typs NaYF 4 :Yb,Er zusätzlich mit La 3+ oder Ce 3+ , um die Emissionsintensitäten einzeln einzustellen.…”

Potassium sodium tartrate-assisted hydrothermal synthesis of BaLuF5:Yb3+/Er3+ nanocrystals

“…The crystal field of host materials for UCNPs should facilitate upconversion emission, to achieve the above desired features. The most efficient host material reported thus far is NaYF 4 , with many studies on NaYF 4 UCNPs having been reported (Jin et al, 2011;Yang et al, 2012). NaYF 4 nanoparticles with good upconversion emission have a hexagonal phase structure, while the cubic phase results in poor upconversion emission.…”