Molecular recognition triggered aptazyme cascade for ultrasensitive detection of exosomes in clinical serum samples

Exosomes have attracted widespread interest due to their inherent advantages in tumor diagnosis and treatment monitoring. However, it is still a big challenge for highly sensitive and specific detection of exosome in real complexed samples. Herein, a molecular recognition triggered aptazyme cascade strategy was developed for ultrasensitive detection of cancer exosomes in clinical serum samples. In this design, one target exosome could capture a large quantity of aptazymes for the first-step signal amplification. And then the captured aptazyme was activated and recycled to release the fluorophore-labelled substrate strand for a cascaded signal amplification. Notably, the activation of aptazyme only occurs when it has bound with target exosome, ensuring a low background. The experimental results show that the limit of detection (LOD) and the limit of quantification (LOQ) are 3.5 × 10³ particles/μL and 1.7 × 10⁴ particles/μL, respectively, which is comparable to the results of most existed fluorescence-based exosome probes. Moreover, this assay possesses high specificity to distinguish exosomes derived from other cell lines. Furthermore, this fluorescence probe was utilized in cancer patient and healthy serum samples successfully, suggesting its great potential for clinical diagnosis and biological studies.