Abstract
Using fluorescence microscopy we have tracked the cellular binding, surface motion, and internalization of polyarginine and polyethylenimine, cationic ligands used for gene and protein delivery. Each ligand was complexed with a quantum dot to provide a photostable probe. Transfection with exogenous DNA was used to relate the observed motion to gene delivery. Cell surface motion was independent of sulfated proteoglycans, but dependent on cholesterol. Cellular internalization required sulfated proteoglycans and cholesterol. These observations suggest that sulfated proteoglycans act as cellular receptors for the cationic ligands, rather than only passive binding sites. Understanding the interaction of polyarginine and polyethylenimine with the plasma membrane may assist in designing more efficient gene delivery systems.