Aptamer-Proximity Ligation Coupled with Rolling Circle Amplification Strategy for an Ultrasensitive Analysis of Tumor-Derived Extracellular Vesicles PD-L1.

Tumor-derived extracellular vesicles (T-EVs) PD-L1 are an important biomarker for predicting immunotherapy response and can help us understand the mechanism of resistance to immunotherapy. However, this is due to the interference from a large proportion of nontumor-derived EVs. It is still challenging to accurately analyze T-EVs PD-L1 in complex human fluids. Herein, a simple and ultrasensitive method based on the dual-aptamer-proximity ligation assay (PLA)-guided rolling circle amplification (RCA) for the analysis of T-EVs PD-L1 was developed. First, dual aptamers with strong binding affinity were utilized for the recognition of EpCAM and PD-L1 on EVs, and then the aptamer-based PLA occurred. With the aid of the high signal amplification ability of RCA guided by the dual-aptamer-based PLA and efficient magnetic separation, the biosensor could realize highly sensitive quantification of EpCAM and PD-L1 dual-positive EVs with a low detection limit of 7.5 particles/μL. In addition, this method based on the aptamer-PLA-guided RCA was used to discriminate cancer patients from healthy donors with 100% accuracy without additional purification. Overall, this strategy might provide a practical tool for the analysis of multiple proteins on EVs, exhibiting great potential in early cancer diagnosis and treatment.