Sentinel lymph nodes (SLN) are the first LN where cancer cells metastasize from the primary tumor. As an activatable fluorescence probe to detect the SLNs, Hagimori et al. developed ternary anionic nanoparticles constructed with fluorophore (TAMRA)-labeled polyamidoamine dendrimer conjugated with diethylenetriaminepentaacetic acid (TAMRA-G4-DTPA), quencher-labeled polyethyleneimine (PEI-QSY7 or PEI-BHQ2), and g-polyglutamic acid, namely TAMRA-G4-DTPA/PEI-QSY7/g-PGA and TAMRA-G4-DTPA/PEI-BHQ2/g-PGA by the electrostatic self-assembly system. The fluorescence of these complexes was quenched by a strong stacking interaction of TAMRA and quenchers, but was dequenched by dissociation of complexes when taken up by inflammatory cells (high populations in LN). They performed fluorescence imaging at 24 h after intradermal injection of TAMRA-G4-DTPA/PEI-QSY7/g-PGA into mouse footpads. Then, TAMRA fluorescence signal was clearly visualized in popliteal lymph node with high contrast.