Fluorogenic resolution of ligand binding by a nucleic acid aptamer.

An ATP-binding nucleic acid aptamer was converted into a solution-phase fluorescence-detected sensor by incorporating a 2'-amine group in a structure that is sensitive to a ligand-induced conformational change in the aptamer. The 2'-amine substitution in the free aptamer reacts efficiently with fluorescamine to yield a fluorescent product detectable by energy transfer to a tethered fluor emitting at 615 nm. In the presence of ATP, the fluorogenic reaction is substantially reduced, both under simplified conditions and in a urine background. Fluorogenic chemistry represents a potentially general approach for creating sensors from aptamers that bind their ligands via induced fit.