Detection of caspase activity induced by local photo activation of mitochondrial KillerRed. Differentiated neuroblastoma cells coexpressing mitochondrially targeted KillerRed and the caspase-3 (DEVD) sensor molecule. (A) Images of mitochondrial KillerRed fluorescence, with corresponding phase contrast image, before (circled) and after photo-activation in selected mitochondria. (B) Corresponding FRET intensity time-lapse images. Time points (see Figure 3) relative to the FRET intensity change are indicated at the top. The frame before the initial drop in FRET intensity was chosen as zero time point. The graph displays relative FRET intensity in the cell body (blue squares), neurite 1 (red dots), neurite 2 (green triangles) and neurite 3 (magenta rhombuses).