CRISPR/Cas13a-Engineered RNA-Based Fluorogenic Biosensor for Label-Free Quantification of RNA in Colorectal Tissues

Colorectal cancer (CRC) continues to represent a serious threat to global health, and its diagnosis faces significant challenges, especially in the early phases of malignant tumors. Herein, we demonstrate that BRD2 RNA can serve as a potent noninvasive CRC biomarker and construct a CRISPR/Cas13a-engineered RNA-based fluorogenic biosensor for label-free detection of BRD2 RNA in colorectal tissues. In this assay, the specific recognition of BRD2 RNA by the substrate probe activates Cas13a/crRNA, leading to the <i>trans</i>-cleavage of the substrate probe and the generation of the T7 promoter sequence. The resulting T7 promoter subsequently induces efficient transcription amplification to synthesize abundant Pepper RNA aptamers that can light up HBC620. Leveraging the synergistic advantages of Cas13a precision, efficient transcription amplification, and superior signal-to-noise ratio of RNA aptamer-fluorophore complex, this fluorogenic biosensor enables sensitive detection of BRD2 RNA down to 0.39 fM and accurate quantification of its expression at the single-cell level. In addition, this fluorogenic biosensor can successfully distinguish CRC patient tissues from adjacent normal tissues based on distinct BRD2 RNA expression profiles. Importantly, the programmability of crRNA makes this fluorogenic biosensor readily adapted for detecting a broad range of RNA targets (e.g., noncoding RNAs and viral RNAs) by simply modifying the spacer sequence of crRNA, providing a new paradigm for early clinical diagnostics.