Labeling efficiency and biodistribution of Technetium-99m labeled nanoparticles: interference by colloidal tin oxide particles.

The interference of colloidal tin oxides on the biodistribution of 99mTechnetium radiolabeled chitosan nanoparticles has been overcome by using sodium borohydride instead of commonly used stannous salts as reducing agent for the reduction of 99mTc (VII)to lower valency states. Biodistribution of radiolabeled chitosan nanoparticles prepared by using stannous chloride method revealed localization of the radioactivity mainly in the liver and spleen while that of radiolabeled chitosan nanoparticles prepared by using sodium borohydride method manifested the presence of radioactivity in blood up to an extent of 10 percent even after 2 h. Interestingly, the reduction of radioactivity in the latter case with the progress of time was not manifested through an increase in activity in the liver. Rather, a time dependent increased accumulation of radioactive materials was observed in the stomach. From the results it has been concluded that the biodistribution is strongly influenced by the presence of colloidal particles of tin oxides and 99mTc labeled chitosan nanoparticles are RES evading and long circulating in blood when Tc (VII)is reduced by sodium borohydride and not by stannous chloride during radiolabeling process.