Figure 1.

Illustration of the aptamer selection process. Typically, four steps are involved in the SELEX cycle. Step 1, the single-stranded DNA or RNA library is incubated with target molecules. Step 2, the bound sequences are separated from unbound strands and recovered for further process. Step 3, the target-binding sequences are amplified by PCR. RNA molecules need additional transcription procedures for amplification purposes. Step 4, single-stranded DNA/RNA sequences are re-generated from PCR products as a new library for the next round of selection. Through several iterative cycles, aptamers can be identified by sequencing and characterization assays.