An RCA-CRISPR-Enhanced SERS Platform for Ultrasensitive and Single-Nucleotide-Resolved Detection of Exosomal miRNA-21 in Early Lung Cancer

Exosomal miRNA-21 has emerged as a promising biomarker for early-stage lung cancer due to its close association with tumor progression and its stability in circulation. However, its low abundance, short sequence length, and high-sequence similarity present significant detection challenges. To address this, we developed an ultrasensitive surface-enhanced Raman scattering (SERS) platform that integrates rolling circle amplification (RCA) with clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 12a (Cas12a) for the detection of exosomal miRNA-21. RCA provides target-dependent amplification with stringent sequence discrimination via padlock probe ligation, while the CRISPR/Cas12a system facilitates robust signal generation through trans-cleavage activity. The final SERS readout enables molecular-level sensitivity by detecting nanotag-labeled cleavage events. The assay achieved a limit of detection as low as 0.62 aM and effectively discriminated miRNA-21 from multiple single- and multinucleotide variants. As a proof of concept, we applied this method to the detection of exosomal miRNA-21 extracted from the serum of 20 early-stage lung cancer patients and 20 healthy controls, achieving 100% sensitivity and 100% specificity (AUC = 1.0) in this preliminary cohort. These findings demonstrate the strong potential of the RCA-CRISPR-SERS platform for noninvasive early-stage lung cancer diagnosis based on exosomal miRNA-21 detection.