Fig. 3. Transfection efficiency and sub-cellular localization of fluorescent siRNA duplex. (A) Confocal microscopy images of neuroblastoma cells transfected with either 400 nM of fluorescein-conjugated siRNA duplex or single strand fluorescein-conjugated siRNA as control. At the indicated times after transfection, N2aS12 cells were fixed with paraformaldehyde and stained with propidium iodide (red) for 10 minutes at room temperature under permeabilization conditions. Images were obtained with a laser scanning confocal microscope. Magnification, x40. (B) A representative fluorescein-siRNA-positive cell was observed as described above. The yellow color indicates red (propidium iodide) and green (fluorescein) dyes superimposed. The dashed line between arrowheads represents the Y-slice optical section. Arrows indicate a single fluorescent dot. N, nucleus.