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The development of magnetic nanoparticles (MNPs) with functional groups has been intensively pursued in recent years.Herein,a simple,versatile,and cost-effective strategy to synthesize water-soluble and amino-functionalized MNPs,based on the thermal decomposition of phthalimide-protected metal–organic precursors followed by deprotection,was developed.The resulting amino-functionalized Fe3O4,MnFe2O4,and Mn3O4 MNPs with particle sizes of about 14.3,7.5,and 6.6 nm,respectively,had narrow size distributions and good dispersibility in water.These MNPs also exhibited high magnetism and relaxivities of r2=107.25 mM1 s1 for Fe3O4,r2=245.75 mM1 s1 for MnFe2O4,and r1=2.74 mM1 s1 for Mn3O4.The amino-functionalized MNPs were further conjugated with a fluorescent dye (rhodamine B) and a targeting ligand (folic acid:FA) and used as multifunctional probes.Magnetic resonance imaging and flow-cytometric studies showed that these probes could specifically target cancer cells overexpressing FA receptors.This new protocol opens a new way for the synthesis and design of water-soluble and amino-functionalized MNPs by an easy and versatile route.