Versatile fluorescence biosensors based on CRISPR/Cas12a for determination of site-specific DNA methylation from blood and tissues.

The identification of DNA methylation at specific sites is crucial for the early detection of cancer since DNA methylation is intimately associated to the occurrence and development of cancer. Herein, two types of sensors that can detect site-specific DNA methylation were developed to meet practical requirements using methylation sensitive restriction endonuclease and CRISPR/Cas12a. To accomplish rapid detection of target, an AciI-mediated CRISPR/Cas12a assay was developed by coupling AciI to recognize DNA methylation with Cas12a to identify site-specific DNA. Since protospacer adjacent motif (PAM)-dependent endonuclease activity and trans-cleavage activity of Cas12a, it is possible to detect site-specific DNA methylation within 2 h with high specificity and acceptable sensitivity. To satisfy the needs of trace target detection, we developed an GlaI-strand displacement amplification (SDA) assisted CRISPR/Cas12a system. The system converts double-stranded methylated DNA to abundant single-stranded by GlaI and SDA. Then, the combination of SDA and CRISPR/Cas12a enable cascades amplification of signal. The approach can therefore be used to detect methylation at different specified sites, even those without PAM, and can increase sensitivity with a detection limit down to 8.19 fM. Importantly, the assay can distinguish between colorectal cancer and precancerous tissue, as well as identify colorectal patients and healthy people. This study provides a new avenue for the development of new biosensors for methylation analysis, and the two methods devised have the potential to meet the multiple requirements of site-specific methylation testing in various clinical settings.