Aptamers are single-stranded nucleic acids (DNA or RNA) that fold into complex structures. They are able to bind with high affinity and specificity to a pre-determined target. They can be defined as “artificial antibodies”. Aptamers are selected from a randomly synthesized oligonucleotide library containing about 1015 different sequences through an iterative in vitro selection process alternating binding and amplification steps.
Selection of aptamers is achieved by mixing the target with the library. Partitioning between target-bound and free sequences is performed by various methods : filtration, chromatography, centrifugation. Target-bound oligonucleotides are PCR-amplified and the resulting pool is mixed with the target under increased selection pressure. The procedure is repeated several times. Among millions of sequences, the strongest binders will «survive » the directed evolution. Aptamers are identified following sequencing.
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