Streptavidin-coated 96-well plates (Perkin Elmer) were coated with 10 pmol of biotin-labeled oligo(dT)16 in 50 ml of PBS per well by incubation at 4 C overnight. Plates were washed twice with PBS and then incubated with the aptamer flanked by oligo(A)16 at the 30 -end (2 pmol per well) at room temperature for 1 h.

Why were the plates coated with Strep and then biotin-labeled oligo? Can't we directly do chemical modification to the aptamer flanked by oligo(A)16 and bind them to the plates?