Multistage Cascade-Hierarchical Nucleic Acid Amplification for Label-Free Ultrasensitive Electrochemical Sensing of Tumor-Associated Extracellular Vesicles

Extracellular vesicles (EVs) are emerging as promising biomarkers for cancer diagnosis, yet the scarcity of tumor-derived EVs (tEVs) in biofluids in early disease stages hampers their sensitive and accurate quantification. Herein, we report an ultrasensitive electrochemical biosensor for highly specific detection of circulating tEVs, which integrates rolling circle amplification, cascade primer exchange reactions, and hierarchically self-assembled DNA architectures (HSDA). Target tEVs are recognized by multivalent aptamers, triggering the release of complementary DNA (cDNA) strands from the aptamer/cDNA duplex. The released cDNAs hybridize with HSDA, and the resulting cDNA/HSDA complex is subsequently immobilized on the electrode surface with the aid of a DNA probe, yielding a strong electrochemical response. The multistage cascade-hierarchical nucleic acid amplification markedly improves detection sensitivity, reaching a limit of 251 particles mL⁻¹ (i.e., < 3 tEVs per 10 μL), corresponding to a 47.6-fold enhancement over the non-HSDA-mediated amplification approach. In addition, we can track the dynamic changes in epithelial cell adhesion molecule-positive tEVs (EpCAM⁺ tEVs) under drug treatment. Furthermore, EpCAM⁺ tEVs can distinguish cancer patients from healthy individuals, underscoring the potential of circulating tEVs for clinical diagnosis and therapy monitoring.