Detection sensitivity of QD 800 imaging in live animals. (A) 1 × 104, 1 × 105 and 1 × 106 QD 800 labeled ES cells were subcutaneously injected on the back of the mice right after labeling. The image was taken 1 hour post injection with excitation filter 465 nm and emission filter 510 nm long-pass, and the quantification of the fluorescent intensity (total signal-background/exposure time (ms) was shown in (B). (C) After images were taken, the mice were imaged again with red excitation light source (640 nm) and the quantification of the fluorescent intensity was shown in (D). Longitudinal imaging of the same representative animal for 1 month shows detection of QD signals up to day 14 (E).