Ultra-small and size tunable PVP-NaGdF4:Dy nanoparticles with high biocompatibility for multimodal tumor imaging

Multimodal imaging nanoprobes by integrating different imaging functions into one nanoplatform can provide more comprehensive and accurate information for the detection of tumors at their early stage, which is crucial to decrease the mortality rate. In this report, highly monodisperse Dy doped NaGdF4 NPs with ultra-small size (2.51 nm and 8.62 nm) were synthesized through a one-step and versatile thermal decomposition method. Then a facile ligand exchange strategy was applied to replace the passivating oleate ligand with an amphiphilic polymer of polyvinylpyrrolidone (PVP). These PVP-NPs not only showed an improved longitudinal relaxivity (r(1) = 6.17 mM(-1) s(-1)) and a higher transverse relaxivity (r(2) = 13.82 mM(-1) s(-1)), but also possessed strong X-ray attenuation properties (48.54 HU L g(-1)). MTT assay, histological analysis and body weight assessment illustrated that the multifunctional NPs were of relatively low toxicity. The influence of particle size on toxicity, biodistribution, elimination pathway and relaxivity was systematically explored. Furthermore, in vivo MR and CT imaging demonstrated that there was considerable signal enhancement in liver, spleen and tumor through intravenous injection. Therefore, it is envisioned that the PVP-NaGdF4: Dy NPs can serve as potential T-1- and T-2-weighted MR and CT imaging contrast agents.