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The synthesis of lanthanide-doped GdVO4 ultrathin nanosheets with great optical and paramagnetic properties for FRET biodetection and in vivo MR imaging.

The development of two dimension (2D) inorganic nanosheets (NSs) with unique physical and chemical properties has been the focus of intense study in recent years. Herein, we report the synthesis of lanthanide ion (Ln3+ = Eu3+, Dy3+)-doped GdVO4 2D tetragonal NSs (with a thickness of ∼5 nm and a width of ∼150 nm) using a facile solvothermal reaction. After the ligand exchange reaction with polyacrylic acid (PAA), the hydrophilic 2D NSs demonstrated a high fluorescence (absolute quantum yield (QY) of 24%) and excellent paramagnetic properties (longitudinal relaxivity reached 37.8 mM-1 s-1). Moreover, this carboxyl functionalized NS could be easily modified for bio-application and exhibited a low toxicity towards cells. Based on the bright fluorescence of the GdVO4:Dy NSs, a sensitive Förster resonance energy transfer (FRET) bioprobe was developed to quantitatively detect the presence of streptavidin. In parallel, the paramagnetic properties of the NSs allows the magnetic resonance imaging (MRI) of integrin α2β1 expression in human prostate cancer. Collectively, multifunctional NSs with a 2D nanostructure demonstrated unique fluorescence and paramagnetic properties, which could be used to construct high performance nanoprobes for biomedical applications.