Aptamer amplification: divide and signal

Aptamers are selected nucleic acids that bind their targets with affinities and specificities that are often comparable to those of monoclonal antibodies.

Although aptamers have been adapted to a wide variety of assay formats, the fact that they are nucleic acids makes them uniquely useful for adaptation to amplification assays. Aptamer-based amplification assays have not previously been reviewed separately.

Aptamers can be used as simple binding reagents and then detected by methods such as the polymerase chain reaction and the rolling circle amplification assay. In addition, though, aptamers can undergo programmed, ligand-dependent conformational changes, or can form unique quarternary structures that lead to amplification.

Analytical assays that involve aptamers and nuleic acid amplification technologies can be used to detect sensitively target proteins, often in the nanomolar or picomolar range. However, in many cases there are no obvious advantages to amplification assays relative to other assay formats. In all likelihood all formats are limited by the dissociation constants of the aptamers themselves. The one exception to this is the proximity ligation assay, where sequence amplification allows the detection of extremely small quantities of ligands relative to background.