Adsorption-Free Self-Priming Direct Digital Dual-crRNA CRISPR/ Cas12a-Assisted Chip for Ultrasensitive Detection of Pathogens

Rapid and sensitive pathogen detection methods are critical for disease diagnosis and treatment. RPA-CRISPR/Cas12 systems have displayed remarkable potential in pathogen detection. A self-priming digital PCR chip is a powerful and attractive tool for nucleic detection. However, the application of the RPA-CRISPR/Cas12 system to the self-priming chip still has great challenges due to the problems of protein adsorption and two-step detection mode of RPA-CRISPR/Cas12. In this study, an adsorption-free self-priming digital chip was developed and a direct digital dual-crRNAs (3D) assay was established based on the chip for ultrasensitive detection of pathogens. This 3D assay combined the advantages of rapid amplification of RPA, specific cleavage of Cas12a, accurate quantification of digital PCR, and point-of-care testing (POCT) of microfluidics, enabling accurate and reliable digital absolute quantification of Salmonella in POCT. Our method can provide a good linear relationship of Salmonella detection in the range from 2.58 x 101 to 2.58 x 104 cells/mL with a limit of detection similar to 0.2 cells/mL within 30 min in a digital chip by targeting the invA gene of Salmonella. Moreover, the assay could directly detect Salmonella in milk without nucleic acid extraction. Therefore, the 3D assay has the significant potential to provide accurate and rapid pathogen detection in POCT. This study provides a powerful nucleic detection platform and facilitates the application of CRISPR/Cas-assisted detection and microfluidic chips.