Sharp Switching of DNAzyme Activity through the Formation of a Cu II ‐Mediated Carboxyimidazole Base Pair

DNAzymes are widely used as functional units for creating DNA‐based sensors and devices. Switching of DNAzyme activity by external stimuli is of increasing interest. Herein we report a Cu II ‐responsive DNAzyme rationally designed by incorporating one of the most stabilizing artificial metallo‐base pairs, a Cu II ‐mediated carboxyimidazole base pair (Im C ‐Cu II ‐Im C ), into a known RNA‐cleaving DNAzyme. Cleavage of the substrate was suppressed without Cu II , but the reaction proceeded efficiently in the presence of Cu II ions. This is due to the induction of a catalytically active structure by Im C ‐Cu II ‐Im C pairing. The on/off ratio was as high as 12‐fold, which far exceeds that of the previously reported DNAzyme with a Cu II ‐mediated hydroxypyridone base pair. The DNAzyme activity can be regulated specifically in response to Cu II ions during the reaction through the addition, removal, or reduction of Cu II . This approach should advance the development of stimuli‐responsive DNA systems with a well‐defined sharp switching function.