Cyclodextrin (CD) is composed of several glucose units and connects by ether bonds. There are three kinds of CDs, α-CD (6 units), β-CD (7 units), and γ-CD (8 units). The heights of the structure are all around 8 Å, while the cavity sizes of them are different, around 5, 6, and 8 Å, respectively.  By comparing the size of the guest molecule and the CD, the binding behavior can be predicted. For instance, if the guest molecule is larger than the CD, it can be assumed that the binding will not occur. Typically, the α-CD can thread onto one PEG chain, while γ-CD can thread onto 2 PEG chains. β-CD can bind with thiophene-based molecule.