One-pot synthesis of a highly selective carboxyl-functionalized superparamagnetic probes for detection of alpha-fetoprotein

We report a simple one-step method for synthesis of water-soluble superparamagnetic manganese ferrite nanoparticles using tetraethylene glycol molecules and 3,6-dioxaoctanedioic acid as the stabilizer and functional agent. The formed nanoparticles had a diameter of 60 nm with a narrow size distribution, and a good stability in both water and PBS. The produced carboxyl-capped nanoparticles materials can be used as probes for magnetic relaxation switches. The surface of the as-prepared nanoparticles is capped with carboxyl groups, which not only resulted good water solubility, but also allowed further conjugation with other functional molecules, thus indicating the potential applications in biosensing and bioimaging. To demonstrate this, conjugating anti-alpha-fetoprotein on the surface of the nanoparticles is employed as magnetic relaxation switches to bind to alpha-fetoprotein, and switching between their dispersed and aggregated states causes changes in the spin-spin relaxation time of their surrounding water protons. A detection platform is developed for the detection of alpha-fetoprotein with a detection limit of 0.15 ng/mL. By appropriately modifying or functionalizing the surface of the nanoparticles, these functionalized magnetic nanoparticles sensor can be widely applied in Magnetic Resonance detection of other biomarkers.