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Biocompatible luminescent nanoparticles on the basis of calcium phosphate Sofia Dembski1, Moritz Milde1, Emeline Dassonneville1, Carsten Gellermann1, Torsten Klockenbring2, Marcel Dyrba3 and Stefan Schweizer3,4 1 Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, Wuerzburg, 97082, Germany 2 Fraunhofer Institute for Molecular Biology and Applied Ecology, Forckenbeckstr. 6, Aachen, 52074, Germany 3 Centre for Innovation Competence SiLi-nano®, Martin Luther University of Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Str. 3, Halle (Saale), 06120, Germany 4 Fraunhofer Center for Silicon Photovoltaics, Walter-Hülse-Str. 1, Halle (Saale), 06120, Germany ABSTRACT Luminescent lanthanide doped SiO2/Hydroxylapatite (HAp) core/shell nanoparticles (NPs) were synthesized by sol-gel technology. The resulting NPs exhibited an amorphous SiO2 core and a crystalline luminescent shell. The formation of the HAp layer was possible at pH 8.5. The characterization of the resulting NPs was done by transmission electron microscopy, X-ray diffraction analysis, inductively-coupled plasma combined with optical emission spectrometry, and photoluminescence spectroscopy. Additionally, the newly developed SiO2/HAp:Ln3+ core/shell NPs were tested for their biocompatibility, e. g. by an in vitro cell culture based assay. INTRODUCTION Materials based on calcium phosphate (CP) are extensively used in medicine due to their chemical composition identical to natural tissue, their excellent biocompatibility and osteoconductivity [1]. Moreover, current studies have shown the possibility to use nanoparticles (NPs) on the basis of CP as luminescent labels [2,3]. In recent years, strategies have been developed to produce luminescent CP-NPs doped with different ions such as Eu3+ and Tb3+ [4]. One advantage of CP is its high capacity to accept various ionic substitutions such as lanthanide (Ln) ions. Ln doped CP-NPs exhibit high photostability, narrow emission bands, and a large Stokes shift [2]. The emission colour can be adjusted throughthe choice of dopants and their combination. The luminescence intensity depends on the concentration of doping ions, the crystal structure of the host material, and the degree of crystallinity [5]. Hence, NPs on the basis of CP have a great application potential in the field of biological and medical diagnostics. In the present work, we describe a method for the synthesis of core/shell-structured luminescent SiO2/HAp:Ln3+-NPs (Ln = Eu, Tb, Dy, Sm) via a sol-gel process. The object of this study was to investigate the effect of pH and Ln3+ concentration on the formation of CP shells around silica cores. The characterization of resulting NPs was done by transmission electron microscopy, Xray diffraction analysis, inductively-coupled plasma combined with optical emission spectrometry, and photoluminescence spectroscopy. In addition, the cytotoxicity of the SiO2/HAp:Ln3+-NPs was tested by a cell culture based XXT viability assay.

EXPERIMENTAL DETAILS SiO2/HAp:Ln3+-NPs (Ln = Eu, Tb, Dy, Sm) were synthesized as previously