Productive screening of single aptamers with ddPCR.

Antibodies have now been widely used for clinical treatment of a number of tumors. However, there are serious problems associated with antibody therapy, such as potential interactions of antibodies with the immune system as well as long production cycles. Recently, aptamers have been found to function similar to the antibodies in terms of affinity and specificity to certain proteins and are attracting much attention for their low immunogenicity, easy chemical synthesis, and efficient penetration into tissues due to its small size. However, how to access high affinity and selectivity aptamer efficiently for further analysis is still open to be resolved. Herein, an aptamer discovery method that combines the continuous flow ddPCR technology with cytometer sorting of beads is reported, such that we have obtained DNA aptamers binding specifically to the PD-1 with the affinity of over 60-fold higher than the best-reported method.