An RCA-Coupled CRISPR/Cas12a Cascade-Enhanced SERS Platform for Ultrasensitive Detection of Exosomal miRNA-21 in Colorectal Cancer Serum

Abstract

Purpose Ultra-sensitive detection of exosomal miR-21 is crucial for the early diagnosis of colorectal cancer. This study aims to develop a cascade amplification platform based on surface-enhanced Raman scattering (SERS), combining rolling circle amplification (RCA) and CRISPR/Cas12a, to enable ultra-sensitive quantitative detection of exosomal miR-21. Methods A SERS substrate was constructed using streptavidin-modified concave gold nanocubes (CGNs), and gold double-stranded probes loaded with Raman reporter molecules were used as SERS probes. The two components are controllably linked via a single-stranded DNA molecule with a thiol group at one end and biotin at the other, forming a stable detection system. Target-triggered RCA generates a repeat sequence, which, under the mediation of crRNA, activates Cas12a cleavage, causing the probe to be released from the substrate surface and resulting in a significant attenuation of the SERS signal. Results This platform achieves three-stage cascading signal amplification via RCA, CRISPR/Cas12a, and SERS, with a detection limit at the femto-mole (fM) level and a total detection time of approximately 80 minutes. The results were consistent with those of qRT-PCR, demonstrating high sensitivity, high specificity, and reliability. Conclusion This study proposes an RCA-CRISPR-SERS cascade amplification platform that provides a highly sensitive and specific method for detecting miR-21 in exosomes, offering potential clinical value for the early diagnosis and dynamic monitoring of colorectal cancer.