Aptamer Selection

Our selection process uses the principles of selective evolution to develop a highly specific aptamer, with an affinity profile of your choice

Aptamers with the desired properties are isolated from the ‘non-binding’ sequences through an iterative process of binding, partitioning and preferential amplification known as in vitro selection.

The aptamer library is incubated directly with the target of interest, allowing the formation of aptamer-target complexes to form. Binding complexes are then partitioned away from unbound/weakly associated species and these species are washed away via elution steps. Target bound oligonucleotides are recovered and amplified by PCR for DNA aptamers, or reverse transcription and subsequent PCR (RT-PCR) for RNA aptamers. The resulting double-stranded DNA is then used to prepare an enriched pool of ssDNA or RNA. This new pool of selected oligonucleotides is used for a binding reaction with the target in the next  in vitro   selection round.

This process is akin to Darwinian evolution. Those aptamers within the diverse library with the highest affinity ‘survive’ the selection process and go on to the next round. These surviving species produce the next ‘generation’ aptamer population with improved qualities from the last. The ‘selection pressure’ can be increased throughout the process in a variety of ways depending on the desired outcome of the selection. For example, the molecules can be evolved to have exquisite selectivity and specificity by the incorporation of negative selection steps, which minimises the enrichment of non-target bound aptamers and favours the survival of aptamers with the desired properties.

Iterative cycles of this process drive the selection of the aptamer population towards relatively few, optimised sequence and structural motifs. These sequences can then be identified and provided to the customer as an alternative to antibodies.