Libraries with longer random regions have more unique sequence motifs than do libraries with shorter random regions. However, not all possible unique sequences can be represented in each selection. For example, a library with a 30 nucleotide random region has the potential for 1.1 x 10¹⁸ unique sequences and a library with a 20 nucleotide random region has 1.1 x 10¹² unique sequences. Typical selections start with 10¹⁵ copies of library. For a library with 20mer random region, approximately 1,000 copies of each unique sequence are present, while for the corresponding library with a 30mer random region, only one out of every 1,000 unique sequences is represented.

In contrast, libraries with shorter random regions will give you a better representation of all possible sequences but are inherently less complex than a library with a longer randomer region. However, once an aptamer is selected shorter aptamers are easier and less expensive to synthesize.

We offer libraries with different random region lengths, allowing the right balance of library complexity and library representation to be experimentally determined for your selection.