One-step synthesis of amino-functionalized up-converting NaYF4:Yb,Er nanoparticles for in vitro cell imaging.

Lidija Mancic,Ivana Dinic,Ljiljana Mojovic,Antonio M. L. M. Costa,Mihailo D. Rabasovic,Aleksandar J. Krmpot,Olivera Milosevic,Marko G. Nikolic,Aleksandra Djukic-Vukovic,Bojan A. Marinkovic

doi:10.1039/c8ra04178d

Abstract

The emerging up-conversion nanoparticles (UCNPs) offer a wide range of biotechnology applications, from biomarkers and deep tissue imaging, to single molecule tracking and drug delivery. Their successful conjugation to biocompatible agents is crucial for specific molecules recognition and usually requires multiple steps which may lead to low reproducibility. Here, we report a simple and rapid one-step procedure for in situ synthesis of biocompatible amino-functionalized NaYF4:Yb,Er UCNPs that could be used for NIR-driven fluorescence cell labeling. X-ray diffraction showed that UCNPs synthesized through chitosan-assisted solvothermal processing are monophasic and crystallize in a cubic α phase. Scanning and transmission electron microscopy revealed that the obtained crystals are spherical in shape with a mean diameter of 120 nm. Photoluminescence spectra indicated weaker green (2H11/2, 4S3/2 → 4I15/2) and stronger red emission (4F9/2 → 4I15/2), as a result of enhanced non-radiative 4I11/2 → 4I13/2 Er3+ relaxation. The presence of chitosan groups at the surface of UCNPs was confirmed by Fourier transform infrared spectroscopy, thermogravimetry and X-ray photoelectron spectroscopy. This provides their enhanced internalization in cells, at low concentration of 10 μg ml−1, without suppression of cell viability after 24 h of exposure. Furthermore, upon 980 nm laser irradiation, the amino-functionalized NaYF4:Yb,Er UCNPs were successfully used in vitro for labeling of two human cell types, normal gingival and oral squamous cell carcinoma.

Highlights

Paper (ET), photon avalanche (PA), cooperative energy transfer (CET) and energy migration-mediated up-conversion (EMU)
Under the guidance of the same concept we have shown that polyethylene glycol (PEG), PVP and EDTA capped NaYF4:Yb,Er nano- and micro-particles could be obtained in a controlled manner through tuning of hydro/ solvothermal processing conditions.[15,16]
The morphology and size of amino-functionalized NaYF4:Yb,Er up-conversion nanoparticles (UCNPs) was evaluated by scanning electron microscopy (Fig. 1a)

Summary

Introduction

Paper (ET), photon avalanche (PA), cooperative energy transfer (CET) and energy migration-mediated up-conversion (EMU). For ET to occur, the excited energy levels of both ions must be resonant, and ions should be in close spatial proximity.[6] For instance, 2F5/2 level of ytterbium resonates well with energy levels of erbium, thulium and holmium, so it is used as a very efficient sensitizer for achieving efficient UC in NaYF4 host. In Yb3+/Er3+ co-doped NaYF4 nanoparticles, green (520 nm and 540 nm) and red (660 nm) emissions are most commonly observed under 980 nm excitation, while violet emission at 415 nm is usually weakened. The emission is dependent on dopants concentration and crystal arrangement of the NaYF4 phase. Green and red emissions are both prominent in the spectra of cubic phase, whereas green dominates in spectra of hexagonal one

Objectives

Methods

Results

Conclusion