Theranostics 2013; 3(4):239-248. doi:10.7150/thno.5113

Research Paper

Multicolor Upconversion Nanoparticles for Protein Conjugation

Stefan Wilhelm1, Thomas Hirsch1, Wendy M. Patterson1, Elisabeth Scheucher2, Torsten Mayr2, Otto S. Wolfbeis1,✉

1. University of Regensburg, Institute of Analytical Chemistry, Chemo- and Biosensors, 93040 Regensburg, Germany.
2. Graz University of Technology, Institute of Analytical Chemistry and Food Chemistry, 8010 Graz, Austria.


We describe the preparation of monodisperse, lanthanide-doped hexagonal-phase NaYF4 upconverting luminescent nanoparticles for protein conjugation. Their core was coated with a silica shell which then was modified with a poly(ethylene glycol) spacer and N-hydroxysuccinimide ester groups. The nanoparticles were characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and dynamic light scattering. The N-hydroxysuccinimide ester functionalization renders them highly reactive towards amine nucleophiles (e.g., proteins). We show that such particles can be conjugated to proteins. The protein-reactive UCLNPs and their conjugates to streptavidin and bovine serum albumin display multicolor emissions upon 980-nm continuous wave laser excitation. Surface plasmon resonance studies were carried out to prove bioconjugation and to compare the affinity of the particles for proteins immobilized on a thin gold film.

Keywords: Upconversion luminescence, nanoparticle, silica coating, Raman spectroscopy, biosensing, magnetic separation, surface plasmon resonance.

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How to cite this article:
Wilhelm S, Hirsch T, Patterson WM, Scheucher E, Mayr T, Wolfbeis OS. Multicolor Upconversion Nanoparticles for Protein Conjugation. Theranostics 2013; 3(4):239-248. doi:10.7150/thno.5113. Available from