Amine-Functionalized Lanthanide-Doped KGdF4 Nanocrystals as Potential Optical/Magnetic Multimodal Bioprobes

Abstract
Amine-functionalized lanthanide-doped KGdF4 nanocrystals, synthesized via a facile one-step solvothermal route by employing polyethylenimine as the surfactant and capping ligand, have been demonstrated to be sensitive time-resolved FRET bioprobes to detect a trace amount of biomolecules such as avidin at a concentration of 5.5 nM and to be potential T1-MRI contrast agents due to a large longitudinal relaxivity of Gd3+ (5.86 S–1·mM–1 per Gd ion and 3.99 × 105 S–1·mM–1 per nanocrystal).