Integration of Switchable DNA-Based Hydrogels with Surfaces by the Hybridization Chain Reaction

A novel method to assemble acrylamide/acrydite DNA copolymer hydrogels on surfaces, specifically gold-coated surfaces, is introduced. The method involves the synthesis of two different copolymer chains consisting of hairpin A, H_A, modified acrylamide copolymer and hairpin B, H_B, acrylamide copolymer. In the presence of a nucleic acid promoter monolayer associated with the surface, the hybridization chain reaction between the two hairpin-modified polymer chains is initiated, giving rise to the cross-opening of hairpins H_A and H_B and the formation of a cross-linked hydrogel on the surface. By the cofunctionalization of the H_A- and H_B-modified polymer chains with G-rich DNA tethers that include the G-quadruplex subunits, hydrogels of switchable stiffness are generated. In the presence of K⁺-ions, the hydrogel associated with the surface is cooperatively cross-linked by duplex units of H_A and H_B, and K⁺-ion-stabilized G-quadruplex units, giving rise to a stiff hydrogel. The 18-crown-6-ether-stimulated elimination of the K⁺-ions dissociates the bridging G-quadruplex units, resulting in a hydrogel of reduced stiffness. The duplex/G-quadruplex cooperatively stabilized hydrogel associated with the surface reveals switchable electrocatalytic properties. The incorporation of hemin into the G-quadruplex units electrocatalyzes the reduction of H₂O₂. The 18-crown-6-ether stimulated dissociation of the hemin/G-quadruplex bridging units leads to a catalytically inactive hydrogel.