Suppose there were DNA or RNA aptamers that bind specifically to a certain terminal amino acid residue. Let's name it aaSA (amino acid specific aptamer). For example, the aptamer binding to terminal methionine residue is named as MetSA.
If such 20 aaSA all existed, then they could be applied to identify the terminal amino acid of a peptide. Concretedly, the peptide sample is immobilized to a solid surface, then all 20 aaSA are introduced and bind to the terminal residue. Extra unbinding aaSA will be washed away, and the binding aaSA will be separated later by another approach (like heating). And by sequencing the binding aaSA we can know the terminal residue of the peptide.
Either N-terminal or C-terminal is OK.
I know mass spectrometry is much more powerful in this task than the method I have supposed. But I still want to know if such aptamer exists or not.
I have searched in Google and Google Scholar, only to find aptamers binding to some intact proteins (rather than short peptides with terminal exposed). The binding site is unknown, possibly not in the terminal.