Figure 3 FTIR analysis of beta-CD (a), aldehyde group functionalized beta-CD (b), crosslinked beta-CD nanocage (c) and crosslinked beta-CD nanocage loaded with DOX (d).
The size of the beta-CD nanocage plays a crucial role in determining the endocytosis pathways for internalizing these nanoparticles into tumor cells. Therefore, the size and evolution process of the beta-CD nanocage were investigated using AFM. First, the size of pristine beta-CD was examined. As shown in Figure 4, the size of individual beta-CD molecules appeared small, with a diameter of approximately 10 nm. However, the larger size observed in the AFM image might be attributed to agglomeration of the molecules. Following the oxidation process, the size of beta-CD showed slight variation, but the agglomeration phenomenon persisted. After crosslinking with cystamine, the resulting nanocage-like structure of beta-CD exhibited a larger size compared to the individual beta-CD, with sizes ranging between 100 nm and 200 nm. It is noted that there was an oversizing of the beta-CD nanocage due to the induced agglomeration between beta-CD molecules. More importantly, after drug loading, DOX-loaded beta-CD exhibited an appropriate size (100-200 nm) for endocytosis. The size of DOX-loaded beta-CD was similar to that of unloaded beta-CD nanocage. This suggests that the physical size of the prepared nanocage could essentially meet the requirements for endocytosis2829[, ].