Aptamer-based folding fluorescent sensor for cocaine

We adapted in two steps a deoxyribonucleotide-based aptamer to signal the r ecognition of cocaine: an instability was engineered in one stem of a three -way junction that forms the cocaine-binding pocket and the resulting short stern was end labeled with a fluorophore and a quencher. In the absence of cocaine, two stems are open, but in its presence they close and the three- way junction forms. This major structural change brings fluorophore and que ncher together thereby signaling the presence and concentration of ligand. The sensor is selective for cocaine over its metabolites. can operate in se rum, and is useful for the screening of cocaine hydrolases.