Molecules show their aptitude

In a review of the history and applications of aptamers, David H.J. Bunka and Peter G. Stockley of the University of Leeds in the UK note that photonics techniques have improved the process of selecting aptamers, which are RNA and DNA that interact with small molecules. They also state that aptamers have been used for biological detection.

The process of selecting aptamers involves mixing nucleic acids and target molecules and eluting the nucleic acids that bind the most tenaciously. The partitioning efficiency of this technique has been improved through the use of surface plasmon resonance. Furthermore, researchers have developed variations on the selection technique that include UV-induced cross-linking of aptamers to their targets, resulting in aptamers with increased binding affinity.

Aptamers can serve as reagents for microarrays, Förster resonance energy transfer experiments and fluorescence quenching experiments. These applications are based on ligand-induced conformational changes. For example, researchers have used a dye that binds only the signaling domain of an aptamer. Upon ligand binding to the recognition domain of that aptamer, the signaling domain binds the dye. In addition, researchers have bound multiple copies of an aptamer to a quantum dot, pairing each to a complementary strand carrying a quencher. Ligand binding displaces the complementary strand, leading to large increases in fluorescence emission. These quantum dots may be used to rapidly detect cell damage or death.

Others have invented a colorimetric assay that employs aptamers bound to gold nanoparticles. Ligand binding induces a conformational change that causes the aggregated nanoparticles to disassemble. These assays may be used to detect illegal drugs or biological and chemical weapons. (Nature Reviews Microbiology, August 2006, pp. 588-596.)