Multivalent Aptamers: Contemporary Engineering Strategies and Biomedical Applications.

Nucleic acid aptamers represent a distinctive class of molecular recognition elements with high binding affinity, excellent chemical stability, and low immunogenicity, making them powerful tools for diverse biomedical applications. Nevertheless, monovalent aptamers are often constrained by limited binding avidity, suboptimal pharmacokinetics, and insufficient biological activation. To address these challenges, multivalent aptamers engineered by assembling multiple units in a well-defined spatial configuration, have emerged to significantly enhance target engagement. This approach improves affinity, specificity, and functional potency, unlocking novel applications inaccessible to monovalent constructs. This review provides a comprehensive overview of recent advances in multivalent aptamer engineering. First, we outline advancements in systematic evolution of ligands by exponential enrichment (SELEX) strategies enabling the direct evolution of multivalent aptamers through rational library design and target-guided selection. Subsequently, we discuss various design approaches for constructing multivalent architectures, alongside their advantages and limitations. Finally, we highlight representative applications, including targeted delivery, therapeutic intervention, molecular imaging, and diagnostics, which capitalize on the multivalency effect to achieve superior biological outcomes in next-generation biomedicine.