Precise selection of aptamers targeting PD-L1 positive small extracellular vesicles on magnetic chips.

A donor-cell-assisted membrane biotinylation strategy was used to modify small extracellular vesicles (sEVs) while minimizing protein damage, and allowed the sEVs to be loaded onto carriers. Biotinylated programmed death-ligand 1 (PD-L1) positive sEVs were used to select for aptamers from a DNA library. PD-L1 negative sEVs from a homologous cell line were found to remove non-specific aptamer sequences to increase the specificity. After just four rounds, high-affinity aptamers for PD-L1 positive sEVs were selected as novel affinity reagents.