Molecular Engineering of Aptamer Self-Assemblies Increases Stability and Targeted Recognition.

Functionally modified aptamer conjugates are promising tools for targeted imaging or treatment of various diseases. However, broad applications of aptamer molecules are limited by their instability. To overcome this challenge, current strategies mostly rely on covalent chemical modification of aptamers, a complicated process that requires case-by-case sequence design, multiple-step synthesis, and purification. Herein, we report a covalent modification-free strategy to enhance the stability of aptamers. This strategy simply utilizes one-step molecular engineering of aptamers with gold nanoclusters (GNCs) to form GNCs@aptamer self-assemblies. Using Sgc8 as a representative aptamer, the resulting GNCs@Sgc8 assemblies enhance cancer-cell-specific binding and sequential internalization by a receptor-mediated endocytosis pathway. Importantly, the GNCs@aptamer self-assemblies resist nuclease degradation for as long as 48 h, compared to the degradation of aptamer alone at 3 h. In parallel, the tumor-targeted recognition and retention of GNCs@aptamer self-assemblies are dramatically enhanced, indicated by a 9-fold signal increase inside the tumor compared to the aptamer alone. This strategy is to avoid complicated chemical modification of aptamers and can be extended to all aptamers. Our work provides a simple, effective, and universal strategy for enhancing the stability of any aptamer or its conjugates, thus expanding their imaging and therapeutic applications.