Concentration of QDs (pmol/g) detected in ALN. 20 pmol were injected subcutaneously in the distal part of the right anterior paw of nude mice. Mice were sacrificed at 5, 15, 30, 60 min and 24 h after injection. Concentration of QDs (pmol/g) was detected in ALN by spectrofluorometry after chemical extraction. Error bars represent SEM, values marked with asterisk were significantly different from control (P < 0.01). ALN: Axillary Lymph Node; QDs: Quantum Dots.