Selective cellular imaging with lanthanide-based upconversion nanoparticles.

Padmaja P Nampi,Paul A Millner,Gin Jose,Alexander Vakurov,Nigel S Scrutton,Lewis E Mackenzie,Sikha Saha

doi:10.1002/jbio.201800256

Padmaja P Nampi, Paul A Millner + Show 5 more

Open Access

https://doi.org/10.1002/jbio.201800256

Copy DOI

Abstract

Upconversion nanoparticles (UCNPs) with sodium yttrium fluoride, NaYF4 (host lattice) doped with Yb3+ (sensitizer) and Er3+ (activator) were synthesized via hydrothermal route incorporating polyethyleneimine (PEI) for their long‐term stability in water. The cationic PEI‐modified UCNPs with diameter 20 ± 4 nm showed a zeta potential value of +36.5 mV and showed an intense, visible red luminescence and low‐intensity green emission with 976 nm laser excitation. The particles proven to be nontoxic to endothelial cells, with a 3‐(4,5‐dimethylthiazol‐2yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay, showing 90% to 100% cell viability, across a wide range of UCNP concentrations (0.3 ng/mL‐0.3 mg/mL) were used in multiphoton imaging. Multiphoton cellular imaging and emission spectroscopy data reported here prove that the UCNPs dispersed in cell culture media are predominantly concentrated in the cytoplasm than the cell nucleus. The energy transfer from PEI‐coated UCNPs to surrounding media for red luminescence in the biological system is also highlighted with spectroscopic measurements. Results of this study propose that UCNPs can, therefore, be used for cytoplasm selective imaging together with multiphoton dyes (eg, 4′,6‐diamidino‐2‐phenylindole (DAPI)) that are selective to cell nucleus.

Highlights

Upconversion is a nonlinear optical process in which multiple photons in the near infrared (NIR) wavelength are absorbed by certain rare earth (RE) doped materials, which emit photons at visible wavelengths via luminescence [1]
We demonstrated that the upconversion nanoparticles (UCNPs) synthesized in this study cause little tissue and cell toxicity and are mainly taken up into the cell cytoplasm
The UCNP zeta potential value of +36.5 mV indicates the cationic surface of the particles and PEI modification increased the water stability of the nanoparticles; an important parameter for cellular uptake in bioimaging applications

Summary

Introduction

Upconversion is a nonlinear optical process in which multiple photons in the near infrared (NIR) wavelength are absorbed by certain rare earth (RE) doped materials, which emit photons at visible wavelengths via luminescence [1]. PEI-modified UCNPs were used for multiphoton imaging within homogenized liver tissue and endothelial cells. HRFE-TEM images of the UCNPs showed a homogeneous distribution with an approximate spherical morphology, with an average particle diameter of 20 Æ 4 nm (mean Æ SD) (Figure 1A-C).

Results

Conclusion