aptamer

noun

ap·​ta·​mer ˈap-tə-mər 

: a short segment of DNA, RNA, or peptide that binds to a specific molecular target (such as a protein)

This aptamer works by binding and blocking a major molecule involved in the body's blood-clotting reaction, called thrombin.

—Debora MacKenzie, New Scientist

Aptamers … are isolated by … the repetitive screening of large pools of randomized molecules for those that bind best to a target.

—Chemical & Engineering News