Boosting split-crRNA CRISPR/Cas12a activity by 3'-end extension of DNA activator for direct microRNA sensing

The unique trans-cleavage activity of CRISPR/Cas12a has been extensively utilized in the domain of biosensing. Nevertheless, the detection of miRNAs using the traditional CRISPR/Cas12a system requires nucleic acid amplification or reverse transcription to convert miRNA into DNA, which increases reaction time and the risk of contamination.

This study presents a split-crRNA CRISPR/Cas12a-based biosensing for direct detection of miRNA. The target miRNA-375 was utilized as the spacer region of the crRNA, facilitating its binding to the truncated scaffold RNA, thereby resulting in the formation of a complete crRNA. More importantly, we discovered that the cleavage activity of split-crRNA CRISPR/Cas12a was significantly enhanced by extending sequences at the 3'-end of the DNA activator. Compared with the conventional split-crRNA CRISPR/Cas12a system, the split-crRNA CRISPR/Cas12a with 24-nucleotide random sequence extension at the 3'-end of the DNA activator exhibited a 6.4-fold increase in activity. The enhancement mechanism of 3'-end extension of DNA activator was discussed. This proposed split-crRNA CRISPR/Cas12a system was applied to detect miRNA-375 with a linear range of 5 pM-1 nM, and the detection limit was estimated to be 0.6 pM (3σ). Furthermore, this system was used to detect miRNA-375 in 10 % diluted human serum, achieving satisfactory recovery rate (98 %-106 %).

This finding indicates that it is feasible to enhance the activity of the split-crRNA CRISPR/Cas12a by extending the 3'-end of the DNA activator, thereby achieving highly sensitive direct detection of miRNA. It is a simple yet effective strategy for enhancing the sensitivity of direct miRNA detection.