Nano Fe <sub> 3 </ Sub> O <sub> 4 </ Sub> Preparation, Surface Modification And Protein Separation And Purification

By means of chemical co-deposition method, modified magnetic nanoparticles were prepared in carboxymethyldextran-water dispersed phase by ultrasonic pretreatment. The product was characterized by IR spectrum, transmission electron microscopy, x-ray diffractometer and vibrating sample magnetometer. The experimental results showed that disperse of composite magnetic nanoparticles is improved by ultrasonic pretreatment method. The magnetic nanopaticles are spheric, uniformly disperse, and an average 50 nm in size. Such modification kept the crystal struvture of the Fe₃O₄ nanoparticles and improved the colloidal stability of nanoparticles in aqueous suspension. These nanoparticles are supermagnetism and have a good saturation magnetization of 35 emu·g^-1.Using bovine serum albumin (BSA) as a model protein, the adsorption and desorption behavior of protein on the magnetic nanoparticles (MNPs) was studied in low concentration. The effects of time, temperatue, proteins concentration, pH value and ionic strength on adsoption behavior of BSA were investigated. The adsorption capacity of the modified MNPs was two times higher than that of nacked MNPs. The adsorption properties are in agreement with Freundlich adsorption mode. The ionic strength and pH value of the solution impact the adsorption properties greatly. The maximal absorption of BSA is achieved at pH4.62, which is close to the isoelectric point of BSA. At this pH, the aborption rate was achieved to 99.5%. About 89.2% BSA could be desorbed from the MNPs using 0.5 mol·L^-1 Na₂HPO₄. It was found that the desorbed BSA could preserve its original structure.Immunomagnetic nanoparticles, containing a magnetic core and a polymer shell, were synthesized by chemical immobilizing the anti-BSA on the surface carboxymethyldextran of modified magnetic nanoparticles. It was found that the dextran-modified magnetic nanoparticles are spheric with an average size of 50 nm. Such modification could keep the the crystal structure of the Fe₃O₄ and improve the stability of magnetic nanoparticles in solution. Based on the unique properties of immunomagnetic microspheres, separation and purification BSA was carried out. The result showed that the imnunomagnetic microspheres could directly separate BSA in the bovine serum and have a low non-specific adsorption. Immunomagnetic MNPs have an adsorption capacity of 21.57 mg·g^-1 and have regeneration property. As a result, the immunomagnetic nanoparticles can be employed as a useful tool for rapid, economical, simple and effective purification of BSA.