CRISPR/Cas12a and Hybridization Chain Reaction-Coregulated Magnetic Relaxation Switching Biosensor for Sensitive Detection of Viable Salmonella in Animal-Derived Foods.

We combined a CRISPR/Cas12a system with a hybridization chain reaction (HCR) to develop an ultrasensitive magnetic relaxation switching (MRS) biosensor for detecting viable Salmonella typhimurium ( S. typhimurium ). Magnetic nanoparticles of two sizes (30 and 1000 nm: MNP 30 and MNP 1000 , respectively) were coupled through HCR. The S. typhimurium gene-activated CRISPR/Cas12a system released MNP 30 from the MNP 1000 -HCR-MNP 30 complex through a trans-cleavage reaction. After magnetic separation, released MNP 30 was collected from the supernatant and served as a transverse relaxation time (T 2 ) signal probe. Quantitative detection of S. typhimurium is achieved by establishing a linear relationship between the change in T 2 and the target gene. The biosensor's limit of detection was 77 CFU/mL (LOD = 3 S / M , S = 22.30, M = 0.87), and the linear range was 10 2 -10 8 CFU/mL. The accuracy for detecting S. typhimurium in real samples is comparable to that of qPCR. Thus, this is a promising method for the rapid and effective detection of foodborne pathogens.