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How We Avoid Immobilizing Targets with FRELEX

Designing aptamers for specific targets needs to be done in a way that ensures you are selecting the aptamers that bind to your target while easily getting rid of those sequences that do not. Typically, this is done by immobilizing the target so that aptamers that bind will stick, while those that do not bind get washed away. The big disadvantage to immobilizing targets is that part of the target is removed from selection due to it being attached to the solid support. This is problematic with every target, from small molecules (entirely removing epitopes for binding) to large proteins (potential to affect folding). We have been able to solve this problem by developing the FRELEX platform, which allows for separation of bound aptamers to the target from those that are not bound in a way that neither the target nor aptamer is immobilized on a surface.


What is FRELEX?

The FRELEX platform utilize a library of random short oligonucleotides on a gold chip. These short oligonucleotides act like a ‘lawn’ that the aptamers can ‘sit’ on by hybridization via Watson-Crick pairing. We first select for the aptamer sequences that sit on this lawn without the target being there. The sequences that bound to the surface are removed and then incubated with the target and reintroduced to the lawn on the gold chip. If the aptamer binds to the target, it will not be able to sit on the lawn of oligonucleotides and we are able to isolate those sequences away from the aptamers that are still sitting on the lawn, and therefore not busy binding to the target.



This approach allows us to select for epitopes on the entire target and not have to worry about selecting aptamers that are non-specifically binding to the immobilization surface used. We continue to use FRELEX to select aptamers for small molecules and proteins to ensure that we are designing the best aptamers for the diagnostic or therapeutic application.


To learn more about the development and ideal applications of FRELEX, get in touch with our team.