We report a novel approach of directly labeling the radioisotope Tc99m with magnetite (Fe3O4) nanoparticles for diagnostic applications. The magnetite nanoparticles were first synthesized from aqueous solutions of Fe(II) and Fe(III) chloride, with addition of ammonium hydroxide. Subsequently, the radioisotope Tc-99m were mixed directly into the reaction solution with ferrite precipitation. The labeling efficiency, of ferrite nanoparticles bound with Tc-99m, is above 99%. As prepared radioactive ferrite nanoparticles were intravenously injected into rats. The biodistribution of radioactivity, monitored by gamma-camera, has shown the uptake of radiomicrospheres can be restrained and transferable in vivo in the living animals by applying an external Nd-Fe-B magnet. Final fate of the radiomicrospheres is to be related with the surface charge of particles. Modification of surface charge of the radiolabeled ferrite nanobeads for clinical targeted diagnosis is discussed.
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