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Organic-inorganic hybrid silica nanoparticles (PM-1, PM-2 and PM-3) with positive surface charge and size below 200 nm were one-pot prepared viaMichael addition between 3-methacryloxypropyl- trimethoxysilane (MPTMS) and polyethylenimine (PEI), followed by hydrolysis and polycondensation of siloxanes. The nanoparticles were characterized by FT-IR, element analysis and particle size analysis. The average sizes of the nanoparticles were 130–180 nm and the surface charge was about 40 mV. The acid–base titration showed that the nanoparticles had higher buffer capacity than PEI 25 kDa. The positively charged nanoparticles can condense negatively charged DNA to form complexes and completely retard the DNA mobility in agarose gel at a weight ratio of 5. The average sizes of PM-1/DNA and PM-2/DNA complexes were below 250 nm and the surface charge of the complexes was in the range of 30–40 mV at the weight ratio of 100. An in vitro transfection assay demonstrated that the transfection efficiencies of the nanoparticles were dependent on the PEI content, and PM-1 showed improved transfection efficiency compared with PEI 25 kDa in the presence of 10% serum. The intracellular trafficking assay of PM-1 nanoparticle/Cy3-labelled DNA complexes in COS-7 cells in the presence of 10% serum indicated that a large amount of complexes crossed the cell membrane and located in the cytoplasm and only a small amount of complexes entered into the cell nucleus after 24 h incubation. The uptake of PM-1 nanoparticle/DNA complexes by COS-7 cells in the presence of serum was higher than that of PEI/DNA complexes. In addition, the cytotoxicity of PM nanoparticles was significantly lower than that of PEI 25 kDa. The results indicate that the synthesized nanoparticles will show potential in nonviral gene delivery.

As a powerful technology to enhance the efficiency of gene delivery, magnetofection has attracted considerable attention in the past decade. In this work, we introduced 6 generation of PAMAM dendrimer modified superparamagnetic nanoparticles (DMSPION-G6) to PEI/DNA polyplexes by a two-step process and enhanced the transfection efficiency of PEI with the help of a magnetic field. We prepared DMSPION-G6/DNA/PEI ternary magnetoplexes by precondensing DMSPION-G6 with DNA at a low mass ratio to yield DMSPION-G6/DNA magnetoplexes with negative surface charge, followed by further coating with branched PEI (25 kDa) via electrostatic interactions. We measured the transfection efficiencies of DMSPION-G6/DNA/PEI ternary magnetoplexes in COS-7, 293T and HeLa cells in the presence or absence of a magnetic field. Compared with PEI/DNA polyplexes, DMSPION-G6/DNA/PEI ternary magnetoplexes exhibited enhanced transfection efficiencies in all the three cell lines when a magnetic field was applied, especially in the presence of 10% FBS. Time-resolved and dose-resolved transfection indicated that high-level transgene expression was achievable with a relatively short incubation time and low DNA dose when magnetofection was employed. Further evidence from Prussian blue staining, quantification of cellular iron concentration and cellular uptake of Cy-3 labelled DNA demonstrated that the magnetic field could quickly gather the magnetoplexes to the surface of target cells and consequently enhanced the uptake of magnetoplexes by the cells. This represents a novel strategy for polycation-based in vitrogene delivery enhanced by a magnetic field.