Objective    To study the acute toxicity of superparamagnetic Fe

3

O

4

nanoparticles (SPFN) to mice.     Methods    The morphology and structural characteristics of SPFN prepared by chemical co-precipitation were determined with a vibratory sample magnetometer under transmission electron microscope. Sixty mice were randomly divided into oral enema group (a total dose of 2 104.8 mg/kg and a volume

of 25 ml/kg)

intra-peritoneal injection group (a total dose of 1 578.6 mg/kg and a volume of 20 ml/kg)

and caudal vein injection group (a total dose of 438.5 mg/kg and a volume of 10 ml/kg)

20 mice in each group

according to different drug administration methods and dosages. Ten mice in each group that received the same dose of normal saline via the same way served as controls. General condition of the mice was observed during experiment

major blood biochemical indicators were analyzed with an automatic biochemical analyzer

and pathological changes in major organs and myeloid tissue were observed with HE staining and Wright staining

respectively.     Results    The diameter of prepared SPFN was 15-20 nm with a saturated magnetization of 21.431 emu/g and a remanent magnetization of 0.102 emu/g. Two weeks after administration of SPFN

no mice died

no significant difference was found in blood biochemical indicators among different groups

and no inflammation

edema

degeneration

necrosis were observed in major organs and bone marrow.     Conclusion    The SPFN we prepared have no acute toxicity to mice.