Visual and colorimetric detection of microRNA in clinical samples based on strand displacement amplification and nanozyme-mediated CRISPR-Cas12a system

The sensitive and accurate detection of target microRNA is especially important for the diagnosis, staging, and treatment of hepatocellular carcinoma (HCC). Herein, we report a simple strand displacement and CRISPR-Cas12a amplification strategy with nanozymes as a signal reporter for the binary visual and colorimetric detection of the HCC related microRNA. Pt@Au nanozymes with excellent peroxidase enzyme activity were prepared and linked to magnetic beads via a single-stranded DNA (ssDNA) linker. The target microRNA was designed to trigger strand displacement amplification and release a DNA promoter to activate the CRISPR-Cas12a system. The activated CRISPR-Cas12a system efficiently cleaved the linker ssDNA and released Pt@Au nanozymes from magnetic beads to induce the colorimetric reaction of 3,3',5,5'-tetramethylbenzidine. The strand displacement amplification converted the single microRNA input into abundant DNA promoter output, which improved the detection sensitivity by over two orders of magnitude. Through integration of strand displacement amplification and the nanozyme-mediated CRISPR-Cas12a system, limits of detection of 0.5 pM and 10 pM for miRNA-21 were achieved with colorimetric and visual readouts, respectively. The proposed strategy can achieve accurate quantitative detection of miRNA-21 in the range from 1 pM to 500 pM. The detection results for miRNA-21 using both colorimetric and visual readouts were validated in 40 clinical serum samples. Significantly, the proposed strategy achieved visual HCC diagnosis with the naked eye and could distinguish distinct Barcelona clinical HCC stages by colorimetric detection, showing good application prospects for sensitive and facile point-of-care testing for HCC.