Highly Sensitive Detection of Let-7a in Different Tumor Cells Based on a Dual Cascade Signal Amplification Strategy

Let-7a is a key microRNA (miRNA) cancer biomarker closely associated with cancer diagnosis and treatment, but its detection is challenging due to its small size and low abundance. In this study, we developed a highly sensitive cascade amplification strategy by integrating catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) to achieve dual-signal amplification. Two functionalized DNA tetrahedron (TDN) probes, TDN-1 and TDN-2 were first assembled by annealing four sequences and modified with four hairpins. Upon activation by let-7a, a cascade reaction occurred through the TDN-1 and TDN-2 probes, generating DNA aggregates through an isothermal CHA-HCR process. Spatial confinement effect played a key role during the CHA-HCR, enabling highly sensitive detection of let-7a while yielding a detection limit of 8.51 pM. This TDN-CHA-HCR reaction was then successfully applied to in situ imaging of endogenous let-7a in living cells, showing great promise in the early diagnosis and treatment of cancers.