Poly(L-lysine) functionalized Eu-doped NaGd(MoO4)2 Nanophosphors for Optical and MRI Imaging

Luminescent rare-earth (RE) based phosphors have attracted recently much attention because of their important applications in several fields including biotechnology (biosensing and bioimaging). Such interest mainly arises from... [ view full abstract ]

Luminescent rare-earth (RE) based phosphors have attracted recently much attention because of their important applications in several fields including biotechnology (biosensing and bioimaging). Such interest mainly arises from the lower toxicity and higher chemical and optical stability of these phosphors when compared with other luminescent materials (quantum dots, organic dyes-based systems, etc.). The presence of Gd3+ cations in these phosphors is also of high interest since it confers to such materials an additional functionality as contrast agents for magnetic resonance imaging (MRI). For most biotechnological applications, the size and shape of these multifunctional materials are to be controlled since such characteristics affects luminescence and magnetic relaxivity and the circulation behaviour of the nanoparticles in the body, their biodistribution and their excretion pathway. In addition, such nanoparticles must be obviously non-toxic and present high colloidal stability in physiological media. To meet the later criterion, the modification of the nanoparticles surface with ligands having different functional groups is usually required. Among RE-based phosphors, those consisting of a molybdate matrix doped with lanthanide (Ln) cations are of particular interest, since this matrix absorb energy in the UV region which is further transferred to such Ln3+ cations, considerably increasing the intensity of their emissions. Surprisingly, the synthesis of uniform Ln:NaGd(MoO4)2 nanoparticles has not been yet achieved. Herein, we report for the first time in literature a method for the synthesis of non-aggregated and highly uniform Eu3+ doped NaGd(MoO4)2 nanoparticles based on a homogeneous precipitation process in a polyol-based medium. The obtained particles present ellipsoidal shape and their size can be varied by adjusting the experimental synthesis parameters. A procedure for the further functionalization of these nanophosphors with polylisine has been also developed in order to improve their colloidal stability in physiological medium (2-Nmorpholino ethanesulfonic acid, MES). A study of the luminescent dynamics as a function of the Eu doping level has been conducted in order to find the optimum nanophosphors, whose magnetic relaxivity and cell viability have also been evaluated for the first time for this system, in order to assess their suitability as multifunctional probes for optical and magnetic bioimaging applications.