Integrating CRISPR-Cas12a with a crRNA-Mediated Catalytic Network for the Development of a Modular and Sensitive Aptasensor

Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas12a, which exhibits excellent target DNAactivated trans-cleavage activity under the guidance of a programmable CRISPR RNA (crRNA), has shown great promise in nextgeneration biosensing technology. However, current CRISPR-Cas12a-based biosensors usually improve sensitivity by the initial nucleic acid amplification, while the distinct programmability and predictability of the crRNA-guided target binding process has not been fully exploited. Herein, we, for the first time, propose a modular and sensitive CRISPR-Cas12a fluorometric aptasensor by integrating an enzyme-free and robust crRNA-mediated catalytic nucleic acid network, namely, Cas12a-CMCAN, in which crRNA acts as an initiator to actuate cascade toehold-mediated strand displacement reactions (TM-SDRs). As a proof of concept, adenosine triphosphate (ATP) was selected as a model target. Owing to the multiturnover of CRISPR-Cas12a trans-cleavage and the inherent recycling amplification network, this method achieved a limit of detection value of 0.16 mu M (20-fold lower than direct Cas12a-based ATP detection) with a linear range from 0.30 to 175 mu M. In addition, Cas12a-CMCAN can be successfully employed to detect ATP levels in diluted human serum samples. Considering the simplicity, sensitivity, and easy to tune many targets by changing aptamer sequences, the Cas12a-CMCAN sensing method is expected to offer a heuristic idea for the development of CRISPR-Cas12a-based biosensors and unlock its potential for general and convenient molecule diagnostics.