Temperature effects were also seen when poly-APS was used for intracellular delivery of lucifer yellow. In the absence of poly-APS no intracellular uptake of lucifer yellow was observed over a 3 h incubation period. After incubation with poly-APS and lucifer yellow (1 mM) for 3 h at 21°C a few individual cells were loaded (A), but after incubation at 7°C almost all cells are filled with lucifer yellow (B). Lipofectamine and LipoGen did not deliver lucifer yellow efficiently. Merged transmission and fluorescence images show that a very modest amount of fluorescence was observed after incubation with lipofectamine and lucifer yellow (1 mM) for 3 h at 21°C (C) and no cells were loaded at 7°C (D). Similarly, with LipoGen, little fluorescence was seen after incubation at 21°C (E) and no cells were loaded at 7°C (F).