To establish a sensing technology of catalytic hairpin self-assembly (CHA) combining with clustered interspaced short palindromic repeats with associated protein 12a (CRISPR-Cas12a) for the detection of exosomal microRNA-21 (miR-21), and to analyze the performance.

Eight patients diagnosed as breast cancer in the First Affiliated Hospital of the Army Military Medical University from September to October 2023 were selected as the breast cancer group; 8 healthy individuals who underwent physical examinations during the same period were selected as the healthy control group. Plasma exosomes and their miR-21 were extracted using the kit. DNA hairpins and CRISPR RNA sequences were designed for miR-21 sequences. The feasibility of detection technology was validated using polyacrylamide gel electrophoresis and fluorescence spectrophotometer. Hairpins concentration, CHA reaction time, Cas12a protein concentration and Cas12a protein reaction time were further optimized. On this basis, miR-21 was detected at different concentrations (0, 0.1, 0.5, 1.0, 2.5, 5.0, 7.5, 10.0 nmol/L), and fluorescence intensity was collected for unary linear regression analysis to evaluate methodological sensitivity; meanwhile, different types of miRNAs (miR-31, miR-26a, miR-192, miR-25-3p) and blank controls were detected to evaluate methodological specificity. A case-control study was conducted to detect the relative expression level of plasma exosomal miR-21 in breast cancer group and healthy control group using this detection technology and reverse transcription PCR (RT-PCR) to evaluate the detection ability of clinical samples.

A detection method for exosomal miR-21 was established using CHA combining with CRISPR-Cas12a. The concentration of miR-21 detected by this method showed a good linear relationship with fluorescence intensity (the linear correlation coefficient 0.966 7), and the linear detection range was 0.1-10.0 nmol/L, and the detection limit was 87.81 pmol/L. The fluorescence intensity of miR-21 was 450.27±23.96 which was higher than that of miR-31, miR-26a, miR-192, miR-25-3p, and the blank group (98.89±7.35, 98.12±2.07, 98.93±2.45, 96.66±2.45, 82.93±3.54, respectively), with statistical significance (P<0.001). The results of RT-PCR showed that the relative expression levels of plasma exosomal miR-21 in the breast cancer group were higher than that in healthy control group (1.83±0.27 vs 0.93±0.12, P<0.001); CHA combining with CRISPR-Cas12a detection technology showed that the relative expression levels of plasma exosomal miR-21 in breast cancer group were higher than that in healthy control group (1.94±0.21 vs 0.98±0.08, P<0.001); There was no significant difference in the relative expression levels of plasma exosomal miR-21 between CHA combining with CRISPR-Cas12a detection technology and reverse transcription PCR in breast cancer group and healthy control group (P>0.05).

In this study, a highly sensitive and specific sensing technology of CHA combining with CRISPR-Cas12a for exosomal miR-21 was established. The results of detecting plasma exosomal miR-21 were consistent with the results of reverse transcription PCR, which can be used for screening of breast cancer patients.

Breast cancer; Exosome; MicroRNA; Catalytic hairpin self-assembly