PEG-ylated cationic CdSe/ZnS QDs as an efficient intracellular labeling agent

Quantum dots (QDs) have size-tunable optical properties, such as photostability, strong photoluminescence and a large Stokes-shift, which make it possible to adapt them to various biological applications. In many cases, surface modi. cation of QDs by carboxylate ligands has been extensively studied. However, there have been few applications on QDs modified with a potential cationic ligand such as amine. In this study, we synthesized robust amine-functionalized QDs and modified their surface with poly( ethylene glycol) for long-term stability. These QDs showed an excellent stability over a broad pH-range and remarkable internalization efficiency into living cells.