Chemical diversity enhances interaction between an X-Aptamer and its target. Numerous modifications have been incorporated in X-Aptamer bead-based libraries.
Several are especially effective:
- Phosphorodithioate (PS2)
- 5-indolyl-dU phosphoramidite (tryptophan functionality)
- 5-hydroxyphenyl-dU phosphoramidite (tyrosine functionality)
- 5-aminoallyl-dU phosphoramidite (lysine functionality)
These unique chemical modifications improve X-Aptamer interaction with targets. Several well-characterized traditional aptamers were selected and synthesized to contain some of the modifications used in X-Aptamers. With just one or two modifications included in the traditional aptamer sequences, binding affinity improved by as much as 2100X (from nanomolar to picomolar) without impacting specificity.