Rational Design of “Turn‐On” Allosteric DNAzyme Catalytic Beacons for Aqueous Mercury Ions with Ultrahigh Sensitivity and Selectivity

The mercury is rising: A DNAzyme with several thymine residues located close to the catalytic site is rendered inactive. However, thymine–Hg2+–thymine interactions transform the DNAzyme into an active enzyme. When fluorophore/quencher pairs are attached, the DNAzyme can be converted into a highly sensitive and selective mercury sensor with a detection limit of 2.4 nM and a greater than 100 000-fold selectivity over other metal ions.