Aptameric sensors based on structural change for diagnosis.

Aptamers are nucleic acids that can bind to various molecules. Because they have some features that are lacking in antibodies, aptamers could serve as alternatives to antibodies. For the purpose of biosensing, we focused on aptamers that undergo structural changes on binding to their target molecules. We constructed an aptamer-based bound/free (B/F) separation system that uses a designed aptamer named the "capturable aptamer". The capturable aptamer changes its structure upon recognizing its target molecule thereby exposing a specific single-strand region. The oligonucleotide that is complementary to this exposed region, named the "capture DNA" is immobilized on a support. This design permits the exclusive capture by the capture DNA of the aptamer bound to its target, and subsequent removal of any unbound aptamer and contaminants by B/F separation. The removal of unbound contaminants or aptamers results in highly sensitive detection at similar levels to those achievable by sandwich-based immunoassay. We describe the construction of a thrombin-detection system by using a capturable aptamer, and we discuss the potential of capturable aptamers in clinical diagnostics.