Programmed DNAzyme-Triggered Dissolution of DNA-Based Hydrogels: Means for Controlled Release of Biocatalysts and for the Activation of Enzyme Cascades

Acrylamide/acrylamide-modified nucleic acid copolymer chains provide building units for the construction of acrylamide–DNA hydrogels. Three different hydrogels are prepared by the cross-linking of the acrylamide–DNA chains with metal ion-dependent DNAzyme sequences and their substrates. The metal ion-dependent DNAzyme sequences used in the study include the Cu2+-, Mg2+-, and Zn2+-dependent DNAzymes. In the presence of the respective metal ions, the substrates of the respective DNAzymes are cleaved, leading to the separation of the cross-linking units and to the dissolution of the hydrogel. The different hydrogels were loaded with a fluorophore-modified dextran or with a fluorophore-functionalized glucose oxidase. Treatment of the different hydrogels with the respective ions led to the release of the loaded dextran or the enzyme, and the rates of releasing of the loaded macromolecules followed the order of Cu2+ > Mg2+ > Zn2+. Also, the different hydrogels were loaded with the enzymes β-galactosidase (β-Gal), glucose oxidase (GOx), or horseradish peroxidase (HRP). In the presence of the appropriate metal ions, the respective hydrogels were dissolved, resulting in the activation of the β-Gal/GOx or GOx/HRP bienzyme cascades and of the β-Gal/GOx/HRP trienzyme cascade.