Cellular uptake and intracellular fate of QD605/Cy5-GTI2040 lipoplexes and polyplexes via flow cytometry analysis. Mean fluorescence intensity of FRET-mediated Cy5 0.5, 1, 2, 4, 24, 48 and 72 h after the cells were treated with lipoplexes and polyplexes at Cy5-GTI2040 concentration of 1 μM. (n=3). From 0.5 h to 4 h after the addition of lipoplexes and polyplexes, more and more lipoplexes and polyplexes were uptaken by the cells. At 24 h, the decay of FRET-mediated Cy5 signal suggested the dissociation of lipoplexes and polyplexes. Then the FRET-mediated Cy5 signal of polyplexes started to level off, indicating the unpacking of polyplexes was almost finished. The FRET-mediated Cy5 signal of lipoplexes, however, was further decreased at 48 h and then leveled off at 72 h, indicating that the majority of lipoplexes broke up 48 h post transfection.