As an alternative method, extraction of plasmid DNA with magnetic separation has been attractive because of their advantages of separation speed, easy use and affordability (Smith 2005). The principle of magnetic purification involves the use of magnetic particles modified with positively charged molecules to adsorb NDA via the electrostatic attraction, because the phosphate backbone of DNA is negatively charged (Tanaka et al. 2009), and then the complex particles binding with DNA are isolated under the action of an external magnetic field. Amino groups (−NH2) are widely used to provide cationic surface charge, and Fe3O4 magnetic particles are mostly preferred for DNA extraction due to their unique magnetic properties.