Fig. 3

The pDNA binding assay and the pDNA protection assay of PEI-SPIO-NPs. a Agarose gel electrophoresis of PEI-SPIO-NPs/pDNA complexes at various N/P ratios. b Electrophoretic mobility analysis of PEI-SPIO-NPs/pDNA after DNase-I treatment. PEI-SPIO-NPs at various N/P ratios and pDNA (3 μg) were incubated at 37 °C in a 5% CO₂ sub-humid environment for 30 min with DNase-I (4 U) in DNase/Mg²⁺ digestion buffer consisting of 50 mM Tris-HCl (pH = 7.6) and 10 mM MgCl₂. DNase I was then inactivated by adding EDTA solution (pH = 8) until the final concentration was 2.5 mM. The sample was then incubated for 15 min at 65 °C, and 10 μL of 1 mg/mL sodium heparin was added to release pDNA from PEI-SPIO-NPs/pDNA. The integrity of pDNA was assessed by 1% agarose gel electrophoresis (90 V, 30 min)