Evaluation of plasmid DNA stability against ultrasonic shear stress and its in vitro delivery efficiency using ionic liquid [Bmim][PF(6)]

The hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF(6)] forms nanostructures with negatively charged plasmid DNA through electrostatic interactions. The formation of plasmid DNA/IL nanostructures was confirmed by measuring the zeta potential of plasmid DNA as well as plasmid DNA/IL nanostructures. The zeta potential of the nanostructures was positive, although plasmid DNA is negatively charged. The positive zeta potential is due to the complexation between plasmid DNA and positively charged ionic liquid [Bmim][PF(6)]. The ability of ionic liquid [Bmim][PF(6)] to protect plasmid DNA against ultrasonic shear stress was also investigated using an agarose gel electrophoretic assay and showed that ionic liquid stabilizes plasmid DNA against ultrasonication. The plasmid DNA and plasmid DNA/IL nanostructures were subjected to ultrasonic shear stress for different time periods and the biological functionality of pristine plasmid DNA (i.e., expression of the eGFP gene) as well as the self-assembled nanostructures was investigated in vitro using three different cell lines, COS7, HEK293 and HeLa. Ionic liquid [Bmim][PF(6)] protected the plasmid DNA against ultrasonic shear stress and also enhanced gene transfection efficiency in vitro. Furthermore, the cytotoxicity of ionic liquid [Bmim][PF(6)] was assayed in vitro using all three cell lines and the toxicity was very low. Therefore, the ionic liquid [Bmim][PF(6)] stabilizes plasmid DNA against ultrasonic shear stress and also enhances its in vitro delivery efficiency.