Dual nuclease-amplified sensitive biosensor for enrofloxacin detection using a DNase I-assisted CRISPR/Cas12a (CRISPR-DNase I) system.

Recent years have witnessed the flourishing of CRISPR/Cas-based biosensors in various fields. However, most of them were developed for nucleic acid detection because non-nucleic acid targets are unable to unleash the cleavage activity of the CRISPR/Cas system directly. To circumvent this problem, activator DNA and deoxyribonuclease I (DNase I) were introduced in this research to render the CRISPR/Cas12a system as a new powerful tool for the detection of enrofloxacin (ENR), a common veterinary drug. In this biosensor, target ENR competed with DNase I- and bovine serum albumin-ENR composite-modified gold nanoparticles (DNase I-AuNPs-BSA-ENR) for the binding sites on the surface of antibody-modified magnetic nanoparticles (immuno-MNPs). Then, the captured DNase I-AuNPs-BSA-ENR degraded the activator DNA in the solution, which inhibited the activation of the CRISPR/Cas12a system. Finally, the fluorescence released by the activated CRISPR/Cas12a system was measured for the quantitative detection of ENR. The ingenious use of activator DNA and DNase I helped transduce the target recognition event into the cleavage activity of the CRISPR/Cas12a system. Moreover, the dual enzymatic amplification from DNase I and the CRISPR/Cas12a system guaranteed the sensitivity of this method with a low detection limit of 0.04 ng/mL. The developed biosensor extended the application of the CRISPR/Cas12a system for the sensitive detection of non-nucleic acid targets, providing a powerful tool in various fields such as environmental monitoring, food safety and clinical diagnosis.