CLSM images of CHO DG44 cells transfected with Cy5-PEI/Cy3-pEGFP-N1 with PEI/DNA ratio of 1:1 (a), 3:1 (b), 5:1 (c), 7:1 (d) for 8 h. 1 DAPI stained nuclei (blue); 2 Cy5-PEI (red); 3 Cy3-pEGFP-N1 (yellow); 4 overlay of Cy5-PEI (red), Cy3-pEGFP-N1 (yellow), DAPI stained nuclei (blue). (Color figure online)