Fig. 3. Polyethylene glycol (PEG) accumulates on the outside of PC12 cells. (A) 1 h after the addition of fluorescently decorated PEG, 3D confocal microscopy revealed that the only labeling above the limit of detection was confined to the surface of acrolein-treated cells. (B) By 2 h post treatment this same result was obtained, whereas at 3 h incubation time (data not shown), PEG was beginning to become apparent within the cells. These 2D representations, captured from 3D animated data sets, do not easily reveal the location of fluorescence when confined to the surface. Animating the 3D reconstruction, however, confirmed this surface labeling.