A CRISPR-enabled fluorometric biosensor for the sensitive detection of heparin antidote protamine based on programmable nuclease Cas12a

Protamine, an arginine-rich polycationic peptide, is a natural food preservative and the only approved antidote to heparin overdose. The detection of protamine is meaningful; however, the detection of protamine is difficult due to the lack of aromatic amino acids in its composition. Herein, we proposed a fluorometric biosensor for the sensitive detection of protamine based on the protamine-mediated regulation of CRISPR/Cas12a collateral cleavage. In the absence of protamine, the DNA probe specifically hybridizes with the Cas12a-crRNA complex, causing the activation of Cas12a. In the presence of protamine, positively charged protamine tightly binds to negatively charged DNA probes through electrostatic interaction, so that the DNA probe cannot hybridize with the Cas12a-crRNA complex. Using a short ssDNA modified with fluorophore and quencher as a reporter, the information of protamine concentration is transduced into DNA information and sensed in a signal turn-off manner. The linear range of this method in protamine detection is 0.04–3.2 μg/mL, yielding a detection limit of 0.03 μg/mL, and the entire sampling-to-response time is about 1 h. This biosensor provides a rationale for using the programmable nuclease Cas12a to detect protamine, and further advances the application of CRISPR technology in bioanalyses.