Cellular uptake of cassettes 1 and 2 in Clone 9 cells. Part a shows that cassette 1 accumulates in the lysosomes and the ER, and perfect energy transfer is observed. Part b shows that cassette 2 labels the lysosomes, cytoplasm, ER and mitochondria, and the extent of energy transfer is organelle specific. Throughout the cassettes were excited at 488 nm ie donor part. Fluorescence images for the donor and acceptor emissions were collected with Band Pass (BP) 500-530 and BP 565-615 emission filters, respectively