In one aspect, the disclosure provides cross-linked materials that include multivalent polynucleotide aptamers that bind a target molecule and conjugates that include two or more separate affinity ligands bound to a conjugate framework, wherein the two or more affinity ligands compete with the target molecule for binding with the aptamers and wherein conjugates are cross-linked within the material as a result of non-covalent interactions between aptamers and affinity ligands on different conjugates. These materials are designed to release amounts of conjugate in response to desired concentrations of the target molecule. Depending on the end application, in various embodiments, the conjugates may also include a drug and/or a detectable label. The drug, detectable label and affinity ligands may be covalently or non-covalently bound to the conjugate framework.
