pH-responsive and switchable triplex-based DNA hydrogels† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00594a

New methods for the preparation of reversible pH-responsive DNA hydrogels based on Hoogsteen triplex structures are described. One system consists of a hydrogel composed of duplex DNA units that bridge acrylamide chains at pH 1⁄4 7.4 and undergoes dissolution at pH 1⁄4 5.0 through the reconfiguration of one of the duplex bridging units into a protonated CG$C triplex structure. The second system consists of a hydrogel consisting of acrylamide chains crosslinked in the presence of an auxiliary strand by Hoogsteen TA$T triplex interaction at pH 1⁄4 7.0. The hydrogel transforms into a liquid phase at pH 1⁄4 10.0 due to the separation of the triplex bridging units. The two hydrogel systems undergo reversible and cyclic hydrogel/solution transitions by subjecting the systems to appropriate pH values. The anti-cancer drug, coralyne, binds specifically to the TA$T triplex-crosslinked hydrogel thereby increasing its stiffness. The pH-controlled release of the coralyne from the hydrogel is demonstrated.