Fig. 1.

Schematic illustration of conventional SELEX. Usually, an initial random library should be synthesized for selection. Then, counter selection is always needed before incubate the library with the targets to remove non-specific binding sequences. After incubation the target-bound sequeneces are collected and amplificated by PCR method. For selecting DNA aptamers, general PCR is enough for the amplification of the secondary library. While, as for selecting RNA aptamers, reverse transcription PCR is introduced before amplification and preparation of secondary library. After several successive rounds of selection, the library is cloned and sequenced followed by evaluation and identification of the enriched aptamers

(Reprinted with permission from Ref. [51]. Copyright © 2015, Elsevier)