Optimizations Nuclease resistance Bioavailability Thermal stability Affinity
2’ or 4’ modifications on sugar ring [34,35]      
5 -modified pyrimidine or 8 -modified purine [6]     [16]
methylphosphonate or phosphorothioate [38]      
LNA or HNA [36,37,39]   [36,37,39]  
3’ or 5’-caps [8,19] [8,19]    
unnecessary nucleotide replacement in single-stranded region [11,23]      
duplex flanks     [21,22]  
truncation       [10]
mutagenesis       [26,32]
oligomerization       [24,26-31]
Table 1: Optimizations on aptamers for different purposes.