The present invention relates to methods for sequencing a polymeric biomolecule and methods for structurally characterizing the same comprising using aptamers. In a preferred embodiment of this invention, these methods relate to using the single polymeric biomolecule. The invention also relates to a method for selecting aptamers useful for sequencing nucleic acids and aptamers generated by the method. The invention also provides aptamers that recognize and bind to AMP, dAMP, GMP, dGMP, CMP and dCMP.