Figure 2: SS-PEI-mediated plasmid DNA transfection in HepG2 cells in vitro. (A) Effect of the N/P ratios on the gene expression levels in HepG2 cells. 25 kDa-branched PEI was used as a control; (B) cell viability of SS-PEI/DNA complexes in HepG2 cells at varying N/P ratios. The percentage of relative cell viability was determined relative to control cells (untreated), taken as 100% cell viability. 25 kDa-branched PEI was used as a control. ***, *: SS-PEI versus PEI; (C) typical HepG2 cells expressing GFP observed under fluorescence microscopy after gene transfection with SS-PEI (a and b) and 25 kDa PEI (ExGen 500) (c and d). (Scale bar: 50 μm).