Paper-based lipid bilayer magnetic interface for ultrasensitive assay of tumor-derived extracellular vesicles PD-L1

Programmed death ligand 1 (PD-L1) of tumor-derived extracellular vesicles (T-EVs) is an important biomarker to predict immunotherapy response. The traditional bioassays of T-EVs PD-L1 are limited by the detection specificity because of the distribution of the signals by PD-L1 from nontumor-derived EVs, which leads to unsatisfactory predictive accuracy. In this work, we developed a simple and ultrasensitive method for the quantification of T-EVs PD-L1 by using the lipid bilayer magnetic interface as the isolation and enrichment carrier along with hybridization chain reaction (HCR) for signal amplification in a paper-based device. First, magnetic beads were covered by liposome bilayers and then anchored with the cholesterol modified epithelial cell adhesion molecule (EpCAM) aptamer to construct a fluid multivalent magnetic interface and realize the high-performance isolation of T-EVs. Moreover, the biosensor relied on the PD-L1 aptamer to initiate the HCR of EVs. Benefiting from the high isolation ability of the lipid bilayer magnetic interface and the high signal amplification ability of HCR, the dual-aptamer-based biosensor is capable of highly sensitive detection of T-EVs with a detection limit as low as 5.0 EVs·µL−1 in a paper-based device. Overall, the paper-based lipid bilayer magnetic interface biosensor not only can serve as an alternative tool for predicting the immunotherapy response but also displays great potential in point-of-care disease diagnosis.