Table 2.

Advantages and disadvantages of different targeting ligands.

Ligand	Targeted drug delivery		Reference
	Advantages	Disadvantages
Antibody	- Barely affected by nucleases in vivo - Different antibodies to bind to the same antigen which has multiple epitopes - High affinity to the target	- High immunogenicity - Easily loss of activity - Susceptible to high temperature and pH changes - Animal-based production	[73]
Aptamer	- Chemical synthesis - Smaller than antibodies (about ten times) - Low immunogenicity - Easy modification	- Susceptible to excess nucleases in a biological system - Low affinity compared to antibody - Limited diversity of possible secondary and tertiary structures	[74]
Peptide	- Peptide libraries for almost any desired target - Extremely high receptor affinity - Only around 10 amino acids - High stability	- More expensive and time-consuming - Limited production of peptides with a predetermined length - More potentially active sequences could be missed	[75]