Prior to transfection, the medium was removed, and the cells were rinsed once with PBS (pH 7.4), then supplied with serum-free medium. The plasmid DNA was mixed with CTS-Fe3O4 and PEG-Fe3O4 as described previously and incubated for 30 minutes at 37°C. DNA/polymer-Fe3O4 complexes were suspended in a serum-free medium to get the final concentrations of 2μg/μL and 1.5mM, respectively. To verify the short exposure to a static magnetic field would improve Inhibitors,research,lifescience,medical transfection efficiency; the cells were placed on a (NdFeB) magnet for 30min at a

distance of 3mm from the magnet surface, which leads to a magnetic flux density of 340mT and a magnetic field gradient perpendicular to the well plate of 14T/m. After a further incubation of 4h, the medium was removed and a new medium containing 10% FCS was added. The cells were incubated with plasmid DNA alone and DNA/polymer-Fe3O4 Inhibitors,research,lifescience,medical complexes under standard conditions and grown in culture medium for 24 hours to allow for EGFP expression. Concurrently, transfection was

performed using nonmagnetic transfection reagents. Chitosan (MWs 45kDa), lipofectamine (BestBio), and PBS were added to an equal volume of DNA as controls. Transfected cells expressing green fluorescent protein were detected Inhibitors,research,lifescience,medical using a Leica fluorescence microscope. 3. Results and Discussion 3.1. Characteristics of Polymer-Fe3O4 Nanoparticles TEM images showed that most of the iron oxide complexes were Inhibitors,research,lifescience,medical approximately spherical (unpublished data). The XRD measurements also indicated that the samples had a cubic crystal system and magnetite Fe3O4 was the dominant body of the polymer-Fe3O4 complexes. The size and zeta potential showed the two samples to have a uniform size of 100nm (Figure 1(a)) and almost the same distribution. The sizes of 10–100nm in diameter are desirable since they are too small not to be eliminated by the reticuloendothelial

system (RES) but too large to be filtered out by the kidneys [15]. CTS-Fe3O4 had a positive charge of about 20mv (Figure 1(b)), and the zeta potential of PEG-Fe3O4 was 0mv. It has been reported that surface charge plays an important Inhibitors,research,lifescience,medical role in determining the efficiency and mechanism of cellular uptake [16]. It is also an important factor to improve stability of polymer-Fe3O4 complexes and to PIK-75 order prevent from further Nature Methods aggregation in aqueous solution via electrostatic repulsion [17]. Zata potential value showed the main binding ability between the polymer Fe3O4 and DNA. The polymer-Fe3O4 complexes were mixed with plasmid DNA according to different volume ratios (1:3, 1:2, 1:1, 2:1, and 3:1) in a 50μL reaction system. It was obvious that the E.E. increased along with the proportion of the magnetic materials mainly because of the electrostatic interactions, surface energy of nanoparticles, and branched structures of polymers. The optimal E.E emerged when the iron oxide complexes were mixed with DNA at 3:1 volume ratio, and the final concentration of DNA and iron oxide was 2μg/μL and 1.5mM respectively.