Bioinspired crystallization, sensitized luminescence and cytocompatibility of citrate-functionalized Ca-substituted europium phosphate monohydrate nanophosphors

Abstract

Bio compatible nanosystems exhibiting long lifetime ( ~millisecond) luminescence features are particu l arly relevant in the field of bioimaging. In this study, citrate functionalized calcium doped europium phosphates nanophosphors of the rhabdophane type were prepared at different synthesis times by a bioinspired crystallization route, consisting in thermal decomplexing of ca2•tEu3• {citrate{phosphate{car bonate solutions. The general formula of this material is Ca«Eu1 a(PO4) 1 a(HP04 l,,•nH2O, with CJ. ranging from 0 to 0.58 and n ~ 1. A thorough characterization of the nanoparticles has been carried out by XRD (including data processing with Topas 6.0), HR TEM, TEM, FTIR, TG{ITTA. ICP, dynamic light scattering (OLS), electrophoretic mobility, and fluorescence spectroscopy. Based on these results a crystallization mechanism involving the filling of cationic sites with Ca21ons associated to a concomitant adjustment of the P04{HPO4 ratio was proposed Upon calcium doping, the aspect ratio of the nanoparticles as well as of the crystalline domains decreased and the relative luminescence intensity (R.LI.) could be modulated. Neither the pH nor the ionic strength, nor the temperature (from 25 to 37 C) affected signif icantly the R.L.I. of particles after resuspension in water, leading to rather steady luminescence features usable in a large domain of conditions. This new class of luminescent compounds has been proved to be fully cytocompatible relative to GTL 16 human carcinoma cells and showed an improved cytocompatibil ity as the Ca2+ content increased when contacted with the more sensitive m17. ASC murine mesenchymal stem cells. These biocompatible nanoparticles thus appear as promising new tailorable tools for biomed ical applications as luminescent nanoprobes.