Figure 2.

Cartoon outlining the ligand exchange reactions and buffer stability conferred by the new ligands. The original surfactants are shown on the left and the incoming cationic ligands in the center. The positively charged “G” in the center image represents the distal guanidinium group. The colloidal stability of Fe@Fe₃O₄–DA-Arg NCs (top right) and CdSe/CdS–TMABr QDs (bottom right) in different buffer and salt solutions is provided as an example. The QDs are shown under UV irradiation. The solutions are (1) PBS, (2) 10 mM HEPES, (3) 50 mM Tris-HCl, (4) 500 mM NaCl, (5) 50 mM NaCl, and (6) 50 mM Na₃PO₄ containing 200 mM NaCl.