Nanoscale Res Lett (2009) 4:982–992 Fig. 5 Representative size distribution proﬁle for PLA- PEG-NPs (a) and DNA-PLA- PEG-NPs (b) A 30 s lsa20 c n i % 10 Size distribution(s) Size distribution(s) B 30 s s a lc20 n i % 10 5 10 50 100 Diameter (nm) 500 1000 5 10 50 100 Diameter (nm) 500 1000 989 Fig. 6 Agarose gel electrophoresis of DNA-PLA-PEG-NPs after being incubated with DNase I at different concentrations. Lane 1–3: DNA-PLA-PEG-NPs incubated with different amount of DNase I at 0.1, 0.2, 0.4 U/lg DNA, respectively, for 30 min; Lane 4: Naked DNA incubated with DNase I at 0.1 U/lg DNA for 30 min; Lane 5: DNA control DNA-PLA-PEG-NPs in vitro could be determined directly and calculated without adjustment. The in vitro drug release property is one of the important characteristics of nanoparticles. Figure 9 showed the accumulative release (expressed as percentage of loaded DNA) versus time curve of DNA from DNA-PLA-PEG-NPs in vitro during 20 days. Release proﬁle of DNA from DNA-PLA-PEG-NPs exhibited an initial burst of release of about 51.7% in the ﬁrst 12 h, followed by slow and continuous release in 20 days. In order to determine the release mechanism of DNA from DNA-PLA-PEG-NPs, the release data were evaluated by )%120 ( m iu100 d e m se 80 a e l re 60 n i 40 D f t o 20 n e t n oC 0 Fig. 7 Plasma stability of DNA-PLA-PEG-NPs. 1: DNA control; 2: Naked DNA incubated in 10% plasma for 1 h; 3: DNA-PLA-PEG- NPs Control; 4: DNA-PLA-PEG-NPs incubated in 10% plasma for 1 h 0 5 20 25 10 15 Time (day) Fig. 8 The proﬁle of content of DNA in release medium with time (n = 3) 123