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(1) Background: Nanomedicine has recently emerged as a promising field, particularly for cancer theranostics. In this context, nanoparticles designed for imaging and therapeutic applications are of interest. We, therefore, studied the encapsulation of upconverting nanoparticles in mesoporous organosilica nanoparticles. Indeed, mesoporous organosilica nanoparticles have been shown to be very efficient for drug delivery, and upconverting nanoparticles are interesting for near-infrared and X-ray computed tomography imaging, depending on the matrix used. (2) Methods: Two different upconverting-based nanoparticles were synthesized with Yb 3+ -Er 3+ as the upconverting system and NaYF 4 or BaLuF 5 as the matrix. The encapsulation of these nanoparticles was studied through the sol-gel procedure with bis(triethoxysilyl)ethylene and bis(triethoxysilyl)ethane in the presence of CTAB. (3) Results: with bis(triethoxysilyl)ethylene, BaLuF 5 : Yb 3+ -Er 3+ , nanoparticles were not encapsulated, but anchored on the surface of the obtained mesoporous nanorods BaLuF 5 : Yb 3+ -Er 3+ @Ethylene. With bis(triethoxysilyl)ethane, BaLuF 5 : Yb 3+ -Er 3+ and NaYF 4 : Yb 3+ -Er 3+ nanoparticles were encapsulated in the mesoporous cubic structure leading to BaLuF 5 : Yb 3+ -Er 3+ @Ethane and NaYF 4 : Yb 3+ -Er 3+ @Ethane, respectively. (4) Conclusions: upconversion nanoparticles were located on the surface of mesoporous nanorods obtained by hydrolysis polycondensation of bis(triethoxysilyl)ethylene, whereas encapsulation occurred with bis(triethoxysilyl)ethane. The later nanoparticles NaYF 4 : Yb 3+ -Er 3+ @Ethane or BaLuF 5 : Yb 3+ -Er 3+ @Ethane were promising for applications with cancer cell imaging or X-ray-computed tomography respectively.

Upconverting nanoparticles (UCNPs) were successfully dendronized for fluorescence medical imaging applications. The structural and morphological characterizations of resulting core/shell NaYF 4 :Yb,Tm@dendrons nanoparticles were performed by means of X-ray diffraction, infrared spectroscopy and transmission electron microscopy. In vitro cytotoxicity assays have evidenced their low toxicity. In vivo fluorescence imaging study was performed in mice upon IR excitation, showing promising imaging capacities at low concentrations (0.5mg/mL) and low power (50mW/cm 2 )., (Copyright © 2016 Elsevier Inc. All rights reserved.)