An ultrasensitive sensing strategy based on CRISPR/Cas13a and T7 RNA polymerase amplification for detection of extracellular vesicles.

Extracellular vesicles (EVs) are important biomarkers for an early diagnosis of lung cancer. Herein, we proposed an ultrasensitive fluorescent sensing platform for EVs detection, which involves aptamer and streptavidin-modified magnetic nanoparticles (SA-MB) magnetic separation technology as well as T7 RNA polymerase-assisted CRISPR/Cas13a system, which can achieve target recycling signal amplification. In this detection method, biotin-modified CD63 aptamer hybridizes first with the aptamer Blocker (T7 promoter) and then binds to SA-MB. When adding EVs, the CD63 aptamer in CD63 aptamer/Blocker/SA-MB complex captures EVs causing the release of Blocker single chain. Subsequently, large amounts of ssRNAs, which are generated with the assistance of Blocker-initiated T7 RNA polymerase, were recognized by CRISPR/Cas13a and trigger its trans-cleavage report probe (F-Q). Eventually, the report probe labeled with fluorescent dye (FAM) and quench group (BHQ) at both ends was cut to produce fluorescent signal. The designed sensor combined this with a signal amplification strategy based on T7 RNA polymerase and CRISPR/Cas13a to significantly enhance the sensitivity and specificity of EVs detection. The use of magnetic separation technology eliminates interference from complex matrices and improves EVs detection efficiency, while the introduction of T7 RNA polymerase and CRISPR/Cas13a enables multiple amplifications of the sensor signals, and enhancing the accuracy and sensitivity of the method. Ultimately, the combination of multiple amplification reactions resulted in a detection limit (LOD) for EVs as low as 60 particles/mL (approximately 1 zmol/L). In addition, this detection method can specifically distinguish EVs from other confounding substances and efficiently detect plasma EVs from lung cancer and healthy individuals in actual samples. Indicating this sensing platform is a valuable tool for early lung cancer detection.