In contrast, the positively charged, PAA-coated Au nanospheres showed much higher adhesion to the cell surface than the other Au nanospheres, as shown in Figure 4B. Finally, ki for the citrate-coated and PVA-coated Au nanospheres were not much different so that the difference in the number of Au nanospheres internalized by the cells for these samples was mainly caused by the different amount of Au nanospheres adsorbed onto the surface (see ka and K). Meanwhile, ki for the PAA-coated Au nanospheres is much higher (5−10 times) than the other two types of samples. This value is comparable to that for Anti-HER2-tagged liposomes (0.012−0.033 min−1),(17) poly(ethylene imine) (0.005−0.007 min−1),(18) and cell penetrating peptides (0.019 min−1).(19) This result implies that the internalization process of the PAA-coated Au nanospheres was as fast as the carriers delivered to the cell via receptor-mediated endocytosis or the other mechanisms (e.g., membrane fusion).
Table 2. Kinetic Parameters Obtained by Fitting the Data in Figur