Chemically induced dimerization (CID) systems, in which two pro-teins dimerize only in the presence of a small molecule ligand, offer versatile tools for small molecule sensing and actuation. However, only a handful of CID systems exist and creating one with the desired sensi-tivity and specificity for any given ligand is an unsolved problem. Here, we developed a combinatorial binders-enabled selection of CID (COMBINES-CID) method broadly applicable to different ligands. We demonstrated a proof-of-principle by generating nanobody-based heterodimerization systems induced by cannabidiol with high ligand selectivity. We applied the CID system to a sensitive sandwich ELISA-like assay of cannabidiol in body fluids with a detection limit of ~0.25 ng/mL. COMBINES-CID provides an efficient, cost-effective solution for expanding the biosensor toolkit for small molecule detection.
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