“Aptamers are small oligonucleotide or peptide molecules that bind tightly to a target molecule. Such functionality exists naturally as part of the riboswitch mechanism, in which an mRNA molecule contains an aptamer sequence which controls the conformation of the mRNA by binding with high specificity to a target molecule (a metabolite or metal ion). Protein expression can thus be regulated, based on the concentration of a target molecule. The identification of aptamers for specific molecules or domains of interest is very useful for research purposes, biodetection, diagnostics, and drug development. Nucleic acid aptamers are frequently engineered using a version of the SELEX (systematic evolution of ligands by exponential enrichment) method. This method allows for the identification of highly specific ligands for many types of targets. The basic SELEX method is as follows:

1. 1. A large pool of random oligonucleotides is created, all of which are of the same length and have identical 5′ and 3′ ends.
   2. These single-stranded oligonucleotides are then exposed to target molecules.
   3. The aptamers which bind to the target are separated from non-bound oligos via nitrocellulose membranes, cross-linking, or capillary electrophoresis.
   4. The selected aptamers undergo PCR amplification.
   5. The amplified aptamers are reverted to single-stranded oligonucleotides and re-exposed to the target under more stringent conditions.
   6. The process is repeated until there remains only aptamers with high specificity for the target.”

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