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:
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.
These phosphoramidites can also impart unique functionality as well as enhanced in vivo stability to oligos used for other applications such as siRNA, antisense, etc.