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, HA, modified acrylamide copolymer and hairpin B, HB, 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 HA and HB and the formation of a cross-linked hydrogel on the surface. By the cofunctionalization of the HA- and HB-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 HA and HB, 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.